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Growth Rates of Fine Aerosol Particles at a Site near Beijing in June 2013

doi: 10.1007/s00376-017-7069-3

  • Growth of fine aerosol particles is investigated during the Aerosol-CCN-Cloud Closure Experiment campaign in June 2013 at an urban site near Beijing. Analyses show a high frequency (∼ 50%) of fine aerosol particle growth events, and show that the growth rates range from 2.1 to 6.5 nm h-1 with a mean value of ∼ 5.1 nm h-1. A review of previous studies indicates that at least four mechanisms can affect the growth of fine aerosol particles: vapor condensation, intramodal coagulation, extramodal coagulation, and multi-phase chemical reaction. At the initial stage of fine aerosol particle growth, condensational growth usually plays a major role and coagulation efficiency generally increases with particle sizes. An overview of previous studies shows higher growth rates over megacity, urban and boreal forest regions than over rural and oceanic regions. This is most likely due to the higher condensational vapor, which can cause strong condensational growth of fine aerosol particles. Associated with these multiple factors of influence, there are large uncertainties for the aerosol particle growth rates, even at the same location.
    摘要: 利用北京附近香河站点2013年6月开展的大型综合观测实验(气溶胶-云凝结核-云闭合实验)数据, 本文研究了气溶胶细颗粒物的增长速率. 分析发现该地区细颗粒增长事件出现频率可以高达50%以上, 增长速率介于2.1至6.5 nm/h, 平均增长速率大约5.1 nm/h. 综合前人研究, 我们发现至少有4种机制可以影响细颗粒物的增长: 气态前体物浓度, 模内凝固, 模外凝固和多相化学反应. 在细粒子增长的初始阶段, 凝结增长起着主导作用; 随着粒子的增长, 凝固效率会增强. 对多个不同区域细粒子增长进行总结发现, 细粒子增长速率在大城市, 城区和森林区域要高于乡村和海洋区域. 很大一个原因是大城市, 城区和森林区域的气态前体物浓度高, 使得该地区细颗粒具有很强的凝结增长. 但同时由于影响细颗粒增长的因子较多, 细颗粒凝结增长速率具有较大的不确定性, 变化幅度较大, 即使是在相同地区.
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  • Albrecht B., 1989: Aerosols,cloud microphysics and fractional cloudiness.Science,245,1227-1230, Increases in aerosol concentrations over the oceans may increase the amount of low-level cloudiness through a reduction in drizzle-a process that regulates the liquid-water content and the energetics of shallow marine clouds. The resulting increase in the global albedo would be in addition to the increase due to enhancement in reflectivity associated with a decrease in droplet size and would contribute to a cooling of the earth's surface.
    Birmili W., H. Berresheim, C. Plass-Dülmer T. Elste, S. Gilge, A. Wiedensohler, and U. Uhrner, 2003: The Hohenpeissenberg aerosol formation experiment (HAFEX): A long-term study including size-resolved aerosol,H2SO4, OH, and monoterpenes measurements. Atmos. Chem. Phys., 3, 361-376, aerosol size distributions (gt; 3 nm) and OH, Hsub2/subSOsub4/sub, and terpene concentrations were measured from April 1998 to August 2000 at a rural continental site in southern Germany. New particle formation (NPF) events were detected on 18% of all days, typically during midday hours under sunny and dry conditions. Surprisingly, most NPF events occurred during spring and winter, whereas the concentrations of aerosol precursors (Hsub2/subSOsub4/sub, monoterpenes) clearly peaked in summer. The number of newly formed particles correlated significantly with solar irradiance and ambient levels of Hsub2/subSOsub4 /suband anti-correlated, especially in the cold season, with relative humidity and the condensational sink provided by pre-existing particles. The particle formation rates were experimentally estimated to be on order of 1 cmsup-3/sup ssup-1/sup. Binary homogeneous Hsub2/subSOsub4/sub-Hsub2/subO nucleation rates calculated from measured Hsub2/subSOsub4/sub were substantially lower than this, even if assuming particle formation under the thermodynamic conditions on top of the boundary layer. The nucleation mode particle growth rates derived from the evolution of the size distribution were 2.6 nm hsup-1/sup on average, with a fraction of 0.7 nm hsup-1/sup attributed to the co-condensation of Hsub2/subSOsub4/sub/Hsub2/subO/NHsub3/sub. Turn-over rate calculations of measured monoterpenes and aromatic hydrocarbons suggest that especially the oxidation products of monoterpenes may contribute to the observed particle growth, although no indications were found that the reaction products of organic compounds would generally control the occurrence of NPF events.
    Coffman D. J., D. A. Hegg, 1995: A preliminary study of the effect of ammonia on particle nucleation in the marine boundary layer.J. Geophys. Res.,100,7147-7160, ternary nucleation model for the H2SO4-NH3-H2O system is presented in an effort to examine the effect of NH3 on heteromolecular homogeneous nucleation in the marine boundary layer (MBL). The results from this nucleation model suggest that ammonia could, in fact, enhance the nucleation rate over that of the binary system, H2SO4-H2O. The magnitude of this enhancement is introduced as an enhancement ratio, which, in principle, is applicable to any binary nucleation rate for H2SO4-H2O. Also presented are preliminary results from a simple aerosol model using this enhancement ratio. These results suggest that under conditions typical of the marine environment it may be possible to produce enough particles to balance the various particle sinks characteristic of the MBL.
    Doyle G. J., 1961: Self-nucleation in the sulfuric acid-water system.The Journal of Chemical Physics35,795-799, Reiss' ``Vector model'' was adapted to calculate the self‐nucleation rate for the sulfuric acid‐water system and similar systems. A numerical calculation was carried out for the typical case of 50% relative humidity at 25°C. It was concluded that rapid self‐nucleation would take place at sulfuric acid partial pressures in the range 10‐8‐10‐10mm Hg. The considerable uncertainty is principally due to lack of data on the partial pressure of sulfuric acid above its aqueous solutions and on the dominant sulfuric acid‐bearing species in humid atmospheres.
    Easter R. C., L. K. Peters, 1994: Binary homogeneous nucleation: Temperature and relative humidity fluctuations, nonlinearity, and aspects of new particle production in the atmosphere. J. Appl. Meteor., 33,775-784, 10.1175/1520-0450(1994)033<0775:BHNTAR>2.0.CO;2.10.1175/1520-0450(1994)0332.0.CO; homogeneous nucleation of sulfuric acid and water vapor is thought to be the primary source of new particles in the marine atmosphere. The rate of binary homogeneous nucleation depends strongly on temperature and the gas-phase concentrations of both sulfuric acid and water vapor. This paper investigates the effects of these nonlinear dependencies on the rate of formation of new particles. An increase of 2°-3°C can reduce the particle formation rate by an order of magnitude. Large-scale fluctuations such as those characteristic of a well-mixed boundary layer can alternately “turn on” and “shut off” the nucleation process, giving rise to regions of new particle formation that are quite localized. These “bursts” of nucleation correspond to higher altitudes in the boundary layer. Small-scale fluctuations, more typical of normal atmospheric turbulence, can increase the binary homogeneous nucleation rate severalfold above the rate calculated based on mean conditions.
    Eisele F. L., P. H. McMurry, 1997: Recent progress in understanding particle nucleation and growth.Philos. Trans. Roy. Soc. B352,191-201, the past half decade, several new tools have become available for investigating particle nucleation and growth. A number of joint field and laboratory studies exploiting some of these new measurement capabilities will be described and new insights shared. The ability to measure OH, SO, HSOand aerosol number and size distributions has made possible a comparison between HSOproduction and loss onto particles in continental air masses. In regions remote from urban emissions, agreement is typically quite good. In contrast, joint field measurements of nucleation precursors such as gas phase HSOand ultrafine particles suggest that classical bimolecular nucleation theory may not properly describe the tropospheric nucleation process. An alternative mechanism, possibly involving ammonia as a stabilizing agent for HSO/HO molecular clusters is discussed. Finally, ultrafine particle measurements are shown to offer new opportunities for studying particle growth rates. Preliminary results suggest that in a remote continental air mass, gas phase HSOuptake is far too slow to explain observed growth rates.
    Garrett T. J., C. F. Zhao, 2006: Increased Arctic cloud longwave emissivity associated with pollution from mid-latitudes.Nature440(7085),787-789, is consensus among climate models that Arctic climate is particularly sensitive to anthropogenic greenhouse gases and that, over the next century, Arctic surface temperatures are projected to rise at a rate about twice the global mean. The response of Arctic surface temperatures to greenhouse gas thermal emission is modified by Northern Hemisphere synoptic meteorology and local radiative processes. Aerosols may play a contributing factor through changes to cloud radiative properties. Here we evaluate a previously suggested contribution of anthropogenic aerosols to cloud emission and surface temperatures in the Arctic. Using four years of ground-based aerosol and radiation measurements obtained near Barrow, Alaska, we show that, where thin water clouds and pollution are coincident, there is an increase in cloud longwave emissivity resulting from elevated haze levels. This results in an estimated surface warming under cloudy skies of between 3.3 and 5.2 W m(-2) or 1 and 1.6 degrees C. Arctic climate is closely tied to cloud longwave emission, but feedback mechanisms in the system are complex and the actual climate response to the described sensitivity remains to be evaluated.
    Ghan S. J., S. E. Schwartz, 2007: Aerosol properties and processes: A path from field and laboratory measurements to global climate models.Bull. Amer. Meteor. Soc.,88,1059-1083, U.S. Department of Energy strategy for improving the treatment of aerosol properties and processes in global climate models involves building up from the microscale with observational validation at every step.
    Gras J. L., 1993: Condensation nucleus size distribution at mawson,Antarctica: seasonal cycle.Atmos. Environ. A,27(9),1417-1425, size distribution of atmospheric condensation nuclei (CN) has been measured at Mawson, on the Antarctic coast, during the period 1985–1990. A clear seasonal cycle is demonstrated in the size distribution with periods of marked bimodality during early spring and autumn. Between these periods, in late spring and summer, steady growth in particle size followed by a period with a relatively stable size distribution and relatively little new particle production were observed. During the remaining part of the year nucleus mode particle concentrations were low, typically less than 20 cm 613 .
    Harrison R. M., J. X. Yin, 2000: Particulate matter in the atmosphere: Which particle properties are important for its effects on health? Science of the Total Environment,249(1-3), 85-101, Whilst epidemiological studies have consistently demonstrated adverse effects of particulate matter exposure on human health, the mechanism of effect is currently unclear. One of the major issues is whether the toxicity of the particles resides in some particular fraction of the particles as defined by chemical composition or size. This article reviews selected data on the major and minor component composition of PM2.5 and PM10 particulate matter showing quite major geographic variations in composition which are not reflected in the exposure-response coefficients determined from the epidemiology which show remarkably little spatial variation. The issue of particle size is more difficult to address due to the scarcity of data. Overall, the data presented provides little support for the idea that any single major or trace component of the particulate matter is responsible for the adverse effects. The issue of particle size is currently unclear and more research is warranted.
    Heintzenberg J., 1994: Properties of the log-normal particle size distribution.Aerosol Science and Technology21,46-48, note presents analytical relationships that connect the parameters of any moment of the log-normal distribution to those of any other, allowing one to harmonize experimental data derived with varying particle sensors. They also make possible calculating essential aerosol parameters that may not be amenable to direct measurements.
    Herrmann, E., Coauthors, 2013: New particle formation in the western Yangtze River Delta: First data from SORPES-station.Atmos. Chem. Phys. Discuss.13,1455-1488, and new particle formation were studied in the western part of the Yangtze River Delta (YRD), at the SORPES station of Nanjing University. Air ions between 0.8 and 42 nm were measured using an air ion spectrometer; a DMPS provided particle size distributions between 6 and 800 nm. Additionally, meteorological data, trace gas concentrations, and PM2.5 values were recorded. During the measurement period from 18 November 2011 to 31 March 2012, the mean total particle concentration was found to be 23 000 cm 3. The mean PM2.5 value was 90 g m 3, well above national limits. During the observations, 26 new particle formation events occurred, typically producing 6 nm particles at a rate of 1 cm 3 s 1, resulting in over 4000 cm 3 new CCN per event. Typical growth rates were between 6 and 7 nm h 1. Ion measurements showed the typical cluster band below 2 nm, with total ion concentrations roughly between 600 and 1000 cm 3. A peculiar feature of the ion measurements were the heightened ion cluster concentrations during the nights before event days. The highly polluted air of the YRD provides both the potential source (SO2) and the sink (particulate matter) for sulfuric acid, leaving radiation as the determining force behind new particle formation. Accordingly, a good correlation was found between new particle formation rate and radiation values.
    IPCC, 2007: Climate Change 2007: The Physical Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change,Solomon et al., Eds.,Cambridge University Press,Cambridge,UnitedKingdomandNewYork,NY,USA,996pp.10.1017/ change 2013: The Physical Science Basis, is the Working Group I (WGI) contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). The WGI contribution extends from observations and paleoclimate information regarding past changes in the climate system, a comprehensive evaluation of climate models, the detection and attribution of observed changes to natural or anthropogenic forcing, through to projected future changes on both near-term and long-term time scales. Human influence on the climate system is now detected with increased certainty, both globally and in most regions. Since the mid-20th century, the increase in anthropogenic greenhouse gas concentrations has led to surface warming over almost the entire globe, while at the same time, the ocean has continued to warm and store energy. Satellite based observations reveal with improved precision that summer sea ice extent is declining rapidly in the Arctic, glaciers are retreating world-wide, and global mean sea level continues to rise. Concurrent with a continued increase in atmospheric COconcentrations, the oceanic uptake of COhas resulted in decreasing pH of seawater since the beginning of the industrial era. Projections of future changes in the climate system to the end of the 21st century are based on a series of new climate models and new scenarios, but are broadly consistent with previous assessment findings, confirming widespread and significant changes across the climate system. Greater warming is projected to occur over land than ocean, with the most rapid warming in the Arctic region. Based on modeled changes in seasonal mean precipitation, the contrast between wet and dry regions, and wet and dry seasons is projected to increase as global temperatures rise. Confidence in projections of global mean sea level rise has increased since the previous IPCC assessment report, and projections now include future rapid ice-sheet dynamical changes. On long time scales, warming is dominated by total emissions of CO, and many changes will persist for centuries even if COemissions were stopped. In 2014 the Fifth Assessment cycle of the IPCC will be completed following the release of the reports of Working Groups II (impacts, adaptation and vulnerability) and Working Groups III (mitigation of climate change), and finally the combined synthesis product based on all three underlying Working Group assessment reports.
    Korhonen P., M. Kulmala, A. Laaksonen, Y. Viisanen, R. McGraw, and J. H. Seinfeld, 1999: Ternary nucleation of H2SO4, NH3, and H2O in the atmosphere. J. Geophys. Res., 104, 26 349-26 353,
    Kreyling W. G., M. Semmler, and W. Möller, 2004: Dosimetry and toxicology of ultrafine particles.Journal of Aerosol Medicine17(3),140-152, While epidemiological studies indicate an association between adverse health effects and ambient ultrafine particle concentrations in susceptible individuals, toxicological studies aim to identify mechanisms which are causal for the gradual transition from the physiological status towards patho-physiological disease. Impressive progress has been made in recent years when objectives changed from classical tests like lung function, etc. to endpoints comprising of particle induced oxidative stress, cell signaling and activation, release of mediators initiating inflammatory processes not only in the respiratory tract but also in the cardio-vascular system. Particularly, the large surface area of ultrafine particles provides a unique interface for catalytic reactions of surface-located agents with biological targets like proteins, cells, etc. However, toxicological studies are hampered by a number of imminent complications when simulating long-term exposure of humans in urban environments with inherited and/or acquired susceptibility (e.g., acute exposure studies at high concentrations either in human subjects or animal models). Yet, based on a conservative estimate results available begin to show an adverse health risk for susceptible individuals and support the epidemiological evidence.
    Kuang C., M. Chen, J. Zhao, J. Smith, P. H. McMurry, and J. Wang, 2012: Size and time-resolved growth rate measurements of 1 to 5 nm freshly formed atmospheric nuclei.Atmos. Chem. Phys.12,3573-3589, study presents measurements of size and time-resolved particle diameter growth rates for freshly nucleated particles down to 1 nm geometric diameter. Novel data analysis methods were developed, de-coupling for the first time the size and time-dependence of particle growth rates by fitting the aerosol general dynamic equation to size distributions obtained at an instant in time. Size distributions of freshly nucleated total aerosol (neutral and charged) were measured during two intensive measurement campaigns in different environments (Atlanta, GA and Boulder, CO) using a recently developed electrical mobility spectrometer with a diethylene glycol-based ultrafine condensation particle counter as the particle detector. One new particle formation (NPF) event from each campaign was analyzed in detail. At a given instant in time during the NPF event, size-resolved growth rates were obtained directly from measured size distributions and were found to increase approximately linearly with particle size from ~1 to 3 nm geometric diameter, increasing from 5.5 0.8 to 7.6 0.6 nm h 1 in Atlanta (13:00) and from 5.6 2 to 27 5 nm h 1 in Boulder (13:00). The resulting growth rate enhancement , defined as the ratio of the observed growth rate to the growth rate due to the condensation of sulfuric acid only, was found to increase approximately linearly with size from ~1 to 3 nm geometric diameter. For the presented NPF events, values for had lower limits that approached ~1 at 1.2 nm geometric diameter in Atlanta and ~3 at 0.8 nm geometric diameter in Boulder, and had upper limits that reached 8.3 at 4.1 nm geometric diameter in Atlanta and 25 at 2.7 nm geometric diameter in Boulder. Nucleated particle survival probability calculations comparing the effects of constant and size-dependent growth indicate that neglecting the strong dependence of growth rate on size from 1 to 3 nm observed in this study could lead to a significant overestimation of CCN survival probability.
    Kulmala M., A. Laaksonen, and L. Pirjola, 1998: Parameterizations for sulfuric acid/water nucleation rates.J. Geophys. Res.,103,8301-8307, present parameterized equations for calculation of sulfuric acid/water critical nucleus compositions and homogeneous nucleation rates. The parameterizations are in agreement with the thermodynamically consistent version of classical binary homogeneous nucleation theory [Wilemski, 1984] incorporating the hydration effect. The new parameterizations produce nucleation rates that differ by several orders of magnitude from the rates predicted by other parameterizations available in the literature. Model simulations of atmospheric aerosol formation show that the use of the new parameterizations may in some cases result in simulated nucleation mode particle number densities that are by a factor of 1000 lower than those obtained using the old parameterizations.
    Kulmala M., L. Pirjola, and J. M. Mäkelä, 2000: Stable sulphate clusters as a source of new atmospheric particles.Nature404,66-69, The formation of new atmospheric particles with diameters of 3-10 nm has been observed at a variety of altitudes and locations. Such aerosol particles have the potential to grow into cloud condensation nuclei, thus affecting cloud formation as well as the global radiation budget. In some cases, the observed formation rates of new particles have been adequately explained by binary nucleation, involving water and sulphuric acid, but in certain locations--particularly those within the marine boundary layer and at continental sites--observed ambient nucleation rates exceed those predicted by the binary scheme. In these locations, ambient sulphuric acid (H2SO4) levels are typically lower than required for binary nucleation, but are sufficient for ternary nucleation (sulphuric acid-ammonia-water). Here we present results from an aerosol dynamics model with a ternary nucleation scheme which indicate that nucleation in the troposphere should be ubiquitous, and yield a reservoir of thermodynamically stable clusters 1-3 nm in size. We suggest that the growth of these clusters to a detectable size (> 3 nm particle diameter) is restricted by the availability of condensable vapour. Observations of atmospheric particle formation and growth from a continental and a coastal site support this hypothesis, indicating that a growth process including ternary nucleation is likely to be responsible for the formation of cloud condensation nuclei.
    Kulmala M., H. Vehkamäki, T. Petäjä, M. Dal Maso, A. Lauri, V.-M. Kerminen, W. Birmili, and P. H. McMurry, 2004a: Formation and growth rates of ultrafine atmospheric particles: A review of observations.Journal of Aerosol Science35,143-176, the past decade, the formation and growth of nanometer-size atmospheric aerosol particles have been observed at a number of sites around the world. Measurements of particle formation have been performed on different platforms (ground, ships, aircraft) and over different time periods (campaign or continuous-type measurements). The development during the 1990s of new instruments to measure nanoparticle size distributions and several gases that participate in nucleation have enabled these new discoveries. Measurements during nucleation episodes of evolving size distributions down to ja:math can be used to calculate the apparent source rate of 3-nm particles and the particle growth rate. We have collected existing data from the literature and data banks (campaigns and continuous measurements), representing more than 100 individual investigations. We conclude that the formation rate of 3-nm particles is often in the range 0.01– ja:math in the boundary layer. However, in urban areas formation rates are often higher than this (up to ja:math ), and rates as high as 10 4 – ja:math have been observed in coastal areas and industrial plumes. Typical particle growth rates are in the range 1– ja:math in mid-latitudes depending on the temperature and the availability of condensable vapours. Over polar areas the growth rate can be as low as ja:math . Because nucleation can lead to a significant increase in the number concentration of cloud condensation nuclei, global climate models will require reliable models for nucleation.
    Kulmala, M., Coauthors, 2004b: Initial steps of aerosol growth.Atmos. Chem. Phys.4,2553-2560, formation and growth of atmospheric aerosols depend on several steps, namely nucleation, initial steps of growth and subsequent amp;ndash; mainly condensational amp;ndash; growth. This work focuses on the initial steps of growth, meaning the growth right after nucleation, where the interplay of curvature effects and thermodynamics has a significant role on the growth kinetics. More specifically, we investigate how ion clusters and aerosol particles grow from 1.5 nm to 20 nm in atmospheric conditions using experimental data obtained by air ion and aerosol spectrometers. The measurements have been performed at a boreal forest site in Finland. The observed trend that the growth rate seems to increase as a function of size can be used to investigate possible growth mechanisms. Such a growth rate is consistent with a recently suggested nano-Kamp;#246;hler mechanism, in which growth is activated at a certain size with respect to condensation of organic vapors. The results also imply that charge-enhance growth associated with ion-mediated nucleation plays only a minor role in the initial steps of growth, since it would imply a clear decrease of the growth rate with size. Finally, further evidence was obtained on the earlier suggestion that atmospheric nucleation and the subsequent growth of fresh nuclei are likely to be uncoupled phenomena via different participating vapors.
    Kulmala M., T. Petäjä, P. Mönkkönen, I. K. Koponen, M. Dal Maso, P. P. Aalto, K. E. J. Lehtinen, and V.-M. Kerminen, 2005: On the growth of nucleation mode particles: Source rates of condensable vapor in polluted and clean environments.Atmos. Chem. Phys.5,409-416, growth properties of nucleation mode particles were investigated. The variation of source rates of condensable vapors in different locations and environmental conditions was analyzed. The measurements were performed in background stations in Antarctica, in Finnish Lapland and Boreal Forest stations (SMEAR I and SMEAR II) as well as in polluted urban sites in Athens, Marseille and New Delhi. Taking advantage of only the measured spectral evolution of aerosol particles as a function of time the formation and growth properties of nucleation mode aerosols were evaluated. The diameter growth-rate and condensation sink were obtained from the measured size distribution dynamics. Using this growth rate and condensation sink, the concentration of condensable vapors and their source rate were estimated. The growth rates and condensation sinks ranged between 0.3-20nmhsup-1/sup and 10sup-4/sup-0.07ssup-1/sup, respectively. The corresponding source rate of condensable vapors varied more than 4 orders of magnitude from 10sup3/sup to over 10sup7/supcmsup-1/supssup-1/sup. The highest condensation sink and source rate values were observed in New Delhi and the smallest values in Antarctica.
    Kulmala, M., Coauthors, 2012: Measurement of the nucleation of atmospheric aerosol particles.Nature Protocols7,1651-1667, formation of new atmospheric aerosol particles and their subsequent growth have been observed frequently at various locations all over the world. The atmospheric nucleation rate (or formation rate) and growth rate (GR) are key parameters to characterize the phenomenon. Recent progress in measurement techniques enables us to measure atmospheric nucleation at the size (mobility diameter) of 1.5 (0.4) nm. The detection limit has decreased from 3 to 1 nm within the past 10 years. In this protocol, we describe the procedures for identifying new-particle-formation (NPF) events, and for determining the nucleation, formation and growth rates during such events under atmospheric conditions. We describe the present instrumentation, best practices and other tools used to investigate atmospheric nucleation and NPF at a certain mobility diameter (1.5, 2.0 or 3.0 nm). The key instruments comprise devices capable of measuring the number concentration of the formed nanoparticles and their size, such as a suite of modern condensation particle counters (CPCs) and air ion spectrometers, and devices for characterizing the pre-existing particle number concentration distribution, such as a differential mobility particle sizer (DMPS). We also discuss the reliability of the methods used and requirements for proper measurements and data analysis. The time scale for realizing this procedure is 1 year.
    Lance S., A. Nenes, J. Medina, and J. N. Smith, 2006: Mapping the operation of the DMT continuous flow CCN counter.Aerosol Science and Technology40,242-254, work thoroughly analyzes a new commercial instrument for measuring Cloud Condensation Nuclei (CCN), the Droplet Measurement Technologies Cylindrical Continuous-Flow Streamwise Thermal Gradient CCN Chamber (CFSTGC). This instrument can measure CCN concentrations at supersaturations from 0.06% to 3% (potentially up to 6%), at a 1 Hz sampling rate that is sufficient for airborne operation. Our analysis employs a fully coupled numerical flow model to simulate the water vapor supersaturation, temperature, velocity profiles and CCN growth in the CFSTGC for its entire range of operation (aerosol sample flow rates 0.25–2.0 L min 61 1, temperature differences 2–15 K and ambient pressures 100–1000 mb). The model was evaluated by comparing simulated instrument responses for calibration aerosol against actual measurements from an existing CCN instrument. The model was used to evaluate the CCN detection efficiency for a wide range of ambient pressures, flow rates, temperature gradients, and droplet growth kinetics. Simulations overestimate the instrument supersaturation when the thermal resistance across the walls of the flow chamber is not considered. We have developed a methodology to determine the thermal resistance and temperature drop across the wetted walls of the flow chamber, by combining simulations and calibration experiments. Finally, we provide parameterizations for determining the thermal resistance, the instrument supersaturation and the optimal detection threshold for the optical particle counter.
    Li Z. Q., F. Niu, J. W. Fan, Y. G. Liu, D. Rosenfeld, and Y. N. Ding, 2011: Long-term impacts of aerosols on the vertical development of clouds and precipitation.Nature Geoscience4,888-894, alter cloud density and the radiative balance of the atmosphere. This leads to changes in cloud microphysics and atmospheric stability, which can either suppress or foster the development of clouds and precipitation. The net effect is largely unknown, but depends on meteorological conditions and aerosol properties. Here, we examine the long-term impact of aerosols on the vertical development of clouds and rainfall frequencies, using a 10-year dataset of aerosol, cloud and meteorological variables collected in the Southern Great Plains in the United States. We show that cloud-top height and thickness increase with aerosol concentration measured near the ground in mixed-phase clouds攚hich contain both liquid water and icehat have a warm, low base. We attribute the effect, which is most significant in summer, to an aerosol-induced invigoration of upward winds. In contrast, we find no change in cloud-top height and precipitation with aerosol concentration in clouds with no ice or cool bases. We further show that precipitation frequency and rain rate are altered by aerosols. Rain increases with aerosol concentration in deep clouds that have a high liquid-water content, but declines in clouds that have a low liquid-water content. Simulations using a cloud-resolving model confirm these observations. Our findings provide unprecedented insights of the long-term net impacts of aerosols on clouds and precipitation.
    Lubin D., A. M. Vogelmann, 2006: A climatologically significant aerosol longwave indirect effect in the Arctic.Nature439,453-456, warming of Arctic climate and decreases in sea ice thickness and extent observed over recent decades are believed to result from increased direct greenhouse gas forcing, changes in atmospheric dynamics having anthropogenic origin, and important positive reinforcements including ice-albedo and cloud-radiation feedbacks. The importance of cloud-radiation interactions is being investigated through advanced instrumentation deployed in the high Arctic since 1997 (refs 7, 8). These studies have established that clouds, via the dominance of longwave radiation, exert a net warming on the Arctic climate system throughout most of the year, except briefly during the summer. The Arctic region also experiences significant periodic influxes of anthropogenic aerosols, which originate from the industrial regions in lower latitudes. Here we use multisensor radiometric data to show that enhanced aerosol concentrations alter the microphysical properties of Arctic clouds, in a process known as the 'first indirect' effect. Under frequently occurring cloud types we find that this leads to an increase of an average 3.4 watts per square metre in the surface longwave fluxes. This is comparable to a warming effect from established greenhouse gases and implies that the observed longwave enhancement is climatologically significant.
    Makela J. M., I. K. Koponen, P. Aalto, and M. Kulmala, 1999: One-year data of submicron size modes of tropospheric background aerosol in southern Finland.J. Aero. Sci.31,595-611, size distributions of submicron atmospheric aerosol were measured between February 1, 1996 and January 31, 1997 at a forest site in Southern Finland. Over 50,000 10-min spectra in the size range 3500 nm were obtained by two parallel DMPSs. The spectra were fitted with two or three lognormal distributions. The occurrence and evolution of different size modes are described, and the seasonal variation of the modes are discussed. Particle formation with subsequent growth is observed to take place in the vicinity of the site mostly during spring time. Particle growth leads to a strong connection between the mean sizes and concentrations of nucleation and Aitken mode particles in spring. During winter time, the modes are more separate and stable in particle size. Also the average concentration of nucleation mode particles ( D p<20 nm) is usually less in winter time, but still a clear nucleation mode is frequently observed. The characteristic features of summer and autumn are not as distinguishable as they are for winter and spring.
    Makela J. M., M. Dal Maso, L. Pirjola, P. Keronen, L. Laakso, M. Kulmala, and A. Laaksonen, 2000: Characteristics of the atmospheric particle formation events observed at a boreal forest site in southern Finland. Boreal Environ. Res.,5, 299-313, ISSN 1239- analysed 184 formation events of new atmospheric aerosol particles, observed at a boreal forest site in Hyytiala, southern Finland. Recognition, selection and classification of the formation events was based on continuous experimental size distribution data for submicron particles from a period 31 January 1996–18 September 1999 (1327 days). The formation events were classified, and their characteristic features such as the starting time and duration of the particle formation, the number of new particles produced, the particle growth rate at the beginning of the formation burst, and the final particle size after the observed 8-hour growth subsequent to formation, were quantified. The formation rate of 3 nm particles, J3, varied in the range 0.001–1 particles cm–3 s–1. The ultrafine particle growth rates varied in the range 1–17 nm h–1. The possible coupling between the apparent formation rate of new particles and their growth rate subsequent to formation was discussed
    McMurry P. H., 2000: A review of atmospheric aerosol measurements.Atmos. Environ.34,1959-1999, developments in atmospheric aerosol measurements are reviewed. The topics included complement those covered in the recent review by Chow (JAWMA 45: 320-382, 1995) which focuses on regulatory compliance measurements and filter measurements of particulate composition. This review focuses on measurements of aerosol integral properties (total number concentration, CCN concentration, optical coefficients, etc.), aerosol physical chemical properties (density, refractive index, equilibrium water content, etc.), measurements of aerosol size distributions, and measurements of size-resolved aerosol composition. Such measurements play an essential role in studies of secondary aerosol formation by atmospheric chemical transformations and enable one to quantify the contributions of various species to effects including light scattering/absorption, health effects, dry deposition, etc. Aerosol measurement evolved from an art to a science in the 1970s following the development of instrumentation to generate monodisperse calibration aerosols of known size, composition, and concentration. While such calibration tools permit precise assessments of instrument responses to known laboratory-generated aerosols, unquantifiable uncertainties remain even when carefully calibrated instruments are used for atmospheric measurements. This is because instrument responses typically depend on aerosol properties including composition, shape, density, etc., which: for atmospheric aerosols, may vary from particle-to-particle and are often unknown. More effort needs to be made to quantify measurement accuracies that can be achieved for realistic atmospheric sampling scenarios. The measurement of organic species in atmospheric particles requires substantial development. Atmospheric aerosols typically include hundreds of organic compounds, and only a small fraction (similar to 10%) of these can be identified by state-of-the-art analytical methodologies. Even the measurement of the total particulate
    Neusüss, C., Coauthors, 2002: Characterization and parameterization of atmospheric particle number,mass, and chemical size distributions in central Europe during LACE-98 MINT.J. Geophys. Res.,107(D21),8127,[1] Intensive measurements of chemical and physical properties of the atmospheric aerosol have been performed at two sites in central Europe during the Melpitz-Intensive (MINT) in November 1997 and the Lindenberg Aerosol Characterization Experiment 1998 (LACE 98) in July and August 1998. Number-size distributions, hygroscopic particle growth, size-segregated gravimetric mass, and size-segregated chemical masses of water-soluble ions and organic and elemental carbon of aerosol particles have been measured. To obtain information on the quality of the different methods, the number-derived, gravimetric, and chemically derived mass distributions are compared. Gravimetric mass of fine particles is attributed completely to chemical composition by carbonaceous material and ions, including an estimate of the water content due to hygroscopic compounds. For the characterization of coarse particles, which contribute less to the total mass concentration, insoluble material has to be included in the mass balance. Mass concentrations calculated from the number-size distributions are well correlated with the gravimetric mass concentration; however, the calculated mass is larger, especially for the Aitken and accumulation modes. The number-derived mass concentration is most sensitive to the sizing uncertainty of the measured number-size distribution. Moreover, the impactor cutoffs and the limited knowledge about the density of the particles (especially with high carbon content) account for a major part of the uncertainties. The overall uncertainty of the calculated mass, determined as the standard deviation of the average value in a Monte Carlo approach, is found to be about 10%. Lognormal parameters for the number-size and volume-size distributions as well as gravimetric mass-size distribution and corresponding chemical composition are presented for different air mass types. Most of the modal parameters do not differ significantly between the air mass types. Higher mass concentrations are mostly due to an increase in size (of Aitken and accumulation mode) rather than an increase in the number of particles in a given mode. Generally, the mass percent carbon content increases with decreasing particle size. The most pronounced difference with season is an increase of carbon content from summer to winter as well as an increase in nitrate content, resulting in a decrease of sulfate. For nitrate a strong dependence on air mass direction is observed. Sulfate and nitrate are predominantly neutralized by ammonium. With the results of the two experiments, quality-controlled mode parameters and corresponding chemical composition of atmospheric aerosol particles in central Europe are now available for application in models.
    Nilsson E. D., M. Kulmala, 1998: The potential for atmospheric mixing processes to enhance the binary nucleation rate.J. Geophys. Res.,103,1381-1389, formation of sulfate aerosol particles due to atmospheric mixing processes is investigated using a classical model for binary nucleation. The nucleation rate is seen to be enhanced when two air parcels with different temperature and relative humidity mix with each other. This is due to the curvature on the vapor pressure diagram, and the whole process is more enhanced in the binary H2SO4 - H2O system when compared with the unary case. If the differences are, for example, 8 K and 60%, the nucleation rate can increase by 2 to 3 orders of magnitude if they are mixed. A brief survey of atmospheric situations that could favor this process is included. The negative feedback effects of coagulation and condensation on the new aerosol particles are found to decelerate the particle formation, but not to prevent it. The damping effect of condensation on preexisting aerosols is examined. It is found that the mixing process is most likely to be important at background conditions, which are the most difficult for explaining nucleation. The mixing effect is also compared with the effect of fluctuations in temperature and relative humidity. In some cases the mixing effect seems to be the most important of the effects. The differences in the effect of mixing on nucleation rate and the limitations of its validity are given for different initial conditions. A simple parameterization of the effect of atmospheric mixing on the binary homogeneous nucleation rate of H2SO4 and H2O is also given.
    Park J., H. Sakurai, K. Vollmers, and P. H. McMurry, 2004: Aerosol size distributions measured at the South Pole during ISCAT.Atmos. Environ.,38 (32),5493-5500, physical size distributions were measured at the South Pole during December 1998 and December 2000 as part of the ISCAT program. The size ranges covered by these measurements were 3 to 25002nm in 1998 and 302nm–202μm in 2000. “Typical background aerosols” measured during both periods were similar. Total aerosol number concentrations ranged from 100 to 30002cm 613 with occasional spikes as high as 10,00002cm 613 . We believe the spikes were due to local emissions. The number mean size of background aerosols ranged from 50 to 7002nm, and total aerosol surface area concentrations were 2.8±0.402μm 2 02cm 613 . Aerosols measured in December 2000 were cleanly separated into “low volume” and “high volume” periods. During the low-volume periods, volume concentrations were 0.07±0.0102μm 3 cm 613 with a volume mean diameter of 0.27±0.0502μm, and these volume concentrations were mostly within a factor two of values that would be expected based on reconstructed mass from particulate chemical composition. Volume concentrations during the “high volume” periods exceed levels that can be explained from aerosol chemistry and calculated light-scattering coefficients exceed values that have been recorded historically. We have been unable to identify why this might have occurred. We observed one 4-h event on December 15, 2000 during which nanoparticles grew slowly from 653.0 to 3.602nm.We believe these particles had recently been formed by nucleation. Because this occurred during a period of stagnation, it is possible that this event was associated with local emissions.
    Raes F., A. Saltelli, and R. Van Dingenen, 1992: Modelling formation and growth of H2SO4-H2O aerosols: Uncertainty analysis and experimental evaluation.Journal of Aerosol Science23,759-771, aerosol dynamics model, AERO2, is presented, which describes the formation of H 2 SO 4 -H 2 O aerosol in a smog chamber. The model is used to analyse how the uncertainties on four input parameters are propagated through an aerosol dynamics model. The input parameters are: the rate of the reaction between SO 2 and OH ( k 1 ), the ratio between the nucleation rate used in AERO2 and that derived from classical nucleation theory ( t n ), the H 2 SO 4 mass accommodation coefficient (α) and a measure of the turbulence intensity in the reactor ( k e ). Uncertainties for these parameters are taken from the literature. One of the results of the analysis is that AERO2 and aerosol dynamics models in general can only predict upper bounds for the total number ( N tot ) and total volume ( V tot ) concentrations of the particles. The uncertainties on N tot and V tot are mainly due to the uncertainties on k 1 , and t n . An uncertainty factor of 20–100 still remains when the uncertainty on k 1 , is reduced to ±5%. Aerosol measurements from three smog chamber experiments have therefore been used, in an attempt to reduce the uncertainty on k 1 and t n . Values for k 1 are obtained in the reduced range 7.8 × 10 6113 to 1.0 × 10 6112 cm 3 s 611 , which is within the range found in the literature. For t n , values in the range 10 4 –10 7 are obtained, which is close to the upper bound of the range in literature. These values for t n are in marked contrast with a recent set of experiments on nucleation in H 2 SO 4 -H 2 O mixtures, which suggests a value for t n of at most 10 615 .
    Rosenfeld D., U. Lohmann, G. B. Raga, C. D. O'Dowd, M. Kulmala, S. Fuzzi, A. Reissell, and M. O. Andreae, 2008: Flood or drought: How do aerosols affect precipitation? Science,321, 1309-1313, serve as cloud condensation nuclei (CCN) and thus have a substantial effect on cloud properties and the initiation of precipitation. Large concentrations of human-made aerosols have been reported to both decrease and increase rainfall as a result of their radiative and CCN activities. At one extreme, pristine tropical clouds with low CCN concentrations rain out too quickly to mature into long-lived clouds. On the other hand, heavily polluted clouds evaporate much of their water before precipitation can occur, if they can form at all given the reduced surface heating resulting from the aerosol haze layer. We propose a conceptual model that explains this apparent dichotomy.
    Shen, X. J., Coauthors, 2011: First long-term study of particle number size distributions and new particle formation events of regional aerosol in the North China Plain.Atmos. Chem. Phys.11,1565-1580, particle number size distributions (size range 0.003-10 μm) were measured between March 2008 and August 2009 at Shangdianzi (SDZ), a rural research station in the North China Plain. These measurements were made in an attempt to better characterize the tropospheric background aerosol in Northern China. The mean particle number concentrations of the total particle, as well as the nucleation, Aitken, accumulation and coarse mode were determined to be 1.2 ± 0.9 × 10, 3.6 ± 7.9 × 10, 4.4 ± 3.4 × 10, 3.5 ± 2.8 × 10and 2 ± 3 cm, respectively. A general finding was that the particle number concentration was higher during spring compared to the other seasons. The air mass origin had an important effect on the particle number concentration and new particle formation events. Air masses from northwest (i.e. inner Asia) favored the new particle formation events, while air masses from southeast showed the highest particle mass concentration. Significant diurnal variations in particle number were observed, which could be linked to new particle formation events, i.e. gas-to-particle conversion. During particle formation events, the number concentration of the nucleation mode rose up to maximum value of 10cm. New particle formation events were observed on 36% of the effective measurement days. The formation rate ranged from 0.7 to 72.7 cms, with a mean value of 8.0 cms. The value of the nucleation mode growth rate was in the range of 0.3-14.5 nm h, with a mean value of 4.3 nm h. It was an essential observation that on many occasions the nucleation mode was able to grow into the size of cloud condensation nuclei (CCN) within a matter of several hours. Furthermore, the new particle formation was regularly followed by a measurable increase in particle mass concentration and extinction coefficient, indicative of a high abundance of condensable vapors in the atmosphere under study.
    Shi J. P., Y. Qian, 2003: Continuous measurements of 3 nm to 10 \upmum aerosol size distributions in St. Louis,M.S. Thesis,Department of Mechanical Engineering,University of Minnesota,Minneapolis,MN55455.
    Spracklen D. V., K. S. Carslaw, M. Kulmala, V.-M. Kerminen, G. W. Mann, and S.-L. Sihto, 2006: The contribution of boundary layer nucleation events to total particle concentrations on regional and global scales.Atmos. Chem. Phys.6,5631-5648, contribution of boundary layer (BL) nucleation events to total particle concentrations on the global scale has been studied by including a new particle formation mechanism in a global aerosol microphysics model. The mechanism is based on an analysis of extensive observations of particle formation in the BL at a continental surface site. It assumes that molecular clusters form at a rate proportional to the gaseous sulfuric acid concentration to the power of 1. The formation rate of 3 nm diameter observable particles is controlled by the cluster formation rate and the existing particle surface area, which acts to scavenge condensable gases and clusters during growth. Modelled sulfuric acid vapour concentrations, particle formation rates, growth rates, coagulation loss rates, peak particle concentrations, and the daily timing of events in the global model agree well with observations made during a 22-day period of March 2003 at the SMEAR II station in Hyyti盲l盲, Finland. The nucleation bursts produce total particle concentrations (>3 nm diameter) often exceeding 10cm, which are sustained for a period of several hours around local midday. The predicted global distribution of particle formation events broadly agrees with what is expected from available observations. Over relatively clean remote continental locations formation events can sustain mean total particle concentrations up to a factor of 8 greater than those resulting from anthropogenic sources of primary organic and black carbon particles. However, in polluted continental regions anthropogenic primary particles dominate particle number and formation events lead to smaller enhancements of up to a factor of 2. Our results therefore suggest that particle concentrations in remote continental regions are dominated by nucleated particles while concentrations in polluted continental regions are dominated by primary particles. The effect of BL particle formation over tropical regions and the Amazon is negligible. These first global particle formation simulations reveal some interesting sensitivities. We show, for example, that significant reductions in primary particle emissions may lead to an increase in total particle concentration because of the coupling between particle surface area and the rate of new particle formation. This result suggests that changes in emissions may have a complicated effect on global and regional aerosol properties. Overall, our results show that new particle formation is a significant component of the aerosol particle number budget.
    Spracklen, D. V., Coauthors, 2008: Contribution of particle formation to global cloud condensation nuclei concentrations.Geophys. Res. Lett.,35,L06808, use a global aerosol microphysics model to predict the contribution of boundary layer (BL) particle formation to regional and global distributions of cloud condensation nuclei (CCN). Including an observationally derived particle formation scheme, where the formation rate of molecular clusters is proportional to gas-phase sulfuric acid to the power one, improves modeled particle size distribution and total particle number concentration at three continental sites in Europe. Particle formation increases springtime BL global mean CCN (0.2% supersaturation) concentrations by 3-20% and CCN (1%) by 5-50%. Uncertainties in particle formation and growth rates must be reduced before the accuracy of these predictions can be improved. These results demonstrate the potential importance of BL particle formation as a global source of CCN.
    Spracklen, D. V., Coauthors, 2010: Explaining global surface aerosol number concentrations in terms of primary emissions and particle formation.Atmos. Chem. Phys.10,4775-4793, synthesised observations of total particle number (CN) concentration from 36 sites around the world. We found that annual mean CN concentrations are typically 3002000 cm 3 in the marine boundary layer and free troposphere (FT) and 100010 000 cm 3 in the continental boundary layer (BL). Many sites exhibit pronounced seasonality with summer time concentrations a factor of 210 greater than wintertime concentrations. We used these CN observations to evaluate primary and secondary sources of particle number in a global aerosol microphysics model. We found that emissions of primary particles can reasonably reproduce the spatial pattern of observed CN concentration (R2=0.46) but fail to explain the observed seasonal cycle (R2=0.1). The modeled CN concentration in the FT was biased low (normalised mean bias, NMB= 88%) unless a secondary source of particles was included, for example from binary homogeneous nucleation of sulfuric acid and water (NMB= 25%). Simulated CN concentrations in the continental BL were also biased low (NMB= 74%) unless the number emission of anthropogenic primary particles was increased or a mechanism that results in particle formation in the BL was included. We ran a number of simulations where we included an empirical BL nucleation mechanism either using the activation-type mechanism (nucleation rate, J, proportional to gas-phase sulfuric acid concentration to the power one) or kinetic-type mechanism (J proportional to sulfuric acid to the power two) with a range of nucleation coefficients. We found that the seasonal CN cycle observed at continental BL sites was better simulated by BL particle formation (R2=0.3) than by increasing the number emission from primary anthropogenic sources (R2=0.18). The nucleation constants that resulted in best overall match between model and observed CN concentrations were consistent with values derived in previous studies from detailed case studies at individual sites. In our model, kinetic and activation-type nucleation parameterizations gave similar agreement with observed monthly mean CN concentrations.
    Sun Y., Z. F. Wang, H. B. Dong, T. Tang, J. Li, X. L. Pan, P. Chen, and J. T. Jayne, 2012: Characterization of summer organic and inorganic aerosols in Beijing,China with an Aerosol Chemical Speciation Monitor.Atmos. Environ.,51,250-259, Aerodyne Aerosol Chemical Speciation Monitor (ACSM) was first deployed in Beijing, China for characterization of summer organic and inorganic aerosols. The non-refractory submicron aerosol (NR-PM 1 ) species, i.e., organics, sulfate, nitrate, ammonium, and chloride were measured in situ at a time resolution of 6515min from 26 June to 28 August, 2011. The total NR-PM 1 measured by the ACSM agrees well with the PM 2.5 measured by a Tapered Element Oscillating Microbalance (TEOM). The average total NR-PM 1 mass for the entire study is 50±30μgm 613 with the organics being the major fraction, accounting for 40% on average. High concentration and mass fraction of nitrate were frequently observed in summer in Beijing, likely due to the high humidity and excess gaseous ammonia that facilitate the transformation of HNO 3 to ammonium nitrate particles. Nitrate appears to play an important role in leading to the high particulate matter (PM) pollution since its contribution increases significantly as a function of aerosol mass loadings. Positive matrix factorization (PMF) of ACSM organic aerosol (OA) shows that the oxygenated OA (OOA) – a surrogate of secondary OA dominates OA composition throughout the day, on average accounting for 64%, while the hydrocarbon-like OA (HOA) shows a large increase at meal times due to the local cooking emissions. Our results suggest that high PM pollution in Beijing associated with stagnant conditions and southern air masses is characterized by the high contribution of secondary inorganic species and OOA from regional scale, whereas the aerosol particles during the clean events are mainly contributed by the local emissions with organics and HOA being the dominant contribution.
    Twomey S., 1974: Pollution and the planetary albedo.Atmos. Environ.8,1251-1256, 90004-3.10.1016/0004-6981(74) of cloud nuclei by pollution can lead to an increase in the solar radiation reflected by clouds. The reflection of solar energy by clouds already may have been increased by the addition of man-made cloud nuclei. The albedo of a cloud is proportional to optical thickness for thin clouds, but changes more slowly with increasing thickness. The optical thickness is increased when the number of cloud nuclei is increased. Although the changes are small, the long-term effect on climate can be profound.
    Weber R. J., J. J. Marti, P. H. McMurry, F. L. Eisele, D. J. Tanner, and A. Jefferson, 1997: Measurements of new particle formation and ultrafine particle growth rates at a clean continental site.J. Geophys. Res.,102,4375-4385, measurements of aerosol particles and their expected gas phase precursors were made at Idaho Hill, Colorado, a remote continental site. This study used apparatus and techniques similar to those employed in an earlier study at the Mauna Loa Observatory, Hawaii [Weber et al., 1995]. New particle formation, identified by the presence of ultrafine particles (nominally 3 to 4 nm diameter), was commonly observed in downslope (westerly) air and was correlated with high sulfuric acid (H2SO4) concentrations, low relative humidity and low particle surface area concentrations. The data point to H2SO4 as a principle nucleation precursor species with typical daytime concentrations between 106 and 107 molecules cm0908083. Particle production was observed at H2SO4 concentrations that are well below predicted values for binary nucleation of H2O and H2SO4, suggesting that another species participated. Particle growth rates were estimated from the data with two independent approaches and in both cases were 0908045 to 10 times higher than can be explained by condensation of H2SO4 and its associated water. This suggests that species in addition to H2S04 were also making large contributions to ultrafine particle growth. Finally, calculated steady-state H2SO4 concentrations were found to be in good agreement with measured values if the mass accommodation coefficient for H2SO4 on aerosol surfaces was assumed equal to 0908041.
    Wu, Z. J., Coauthors, 2007: New particle formation in Beijing,China: Statistical analysis of a 1-year data set.J. Geophys. Res.,112(D9),D09209,[1] Particle number size distributions between 3 nm and 10 0204m were measured in Beijing, China. New particle formation events were observed on around 40% of the measurement days from March 2004 to February 2005 and were generally observed under low relative humidity and sunny conditions. Though occurring during all seasons, new particle formation events had highest frequency in spring and lowest frequency in summer. Events were classified as 090008clean090009 or 090008polluted090009 groups mainly according to the condensational sink and the local wind. The formation rate range was from 3.3 to 81.4 cm0908083 s0908081. The growth rate varied from 0.1 to 11.2 nm h0908081. The seasonal variation of condensable vapor concentration showed the highest values during summer months due to enhanced photochemical and biological activities as well as stagnant air masses preventing exchange with cleaner air.
    Yu, F. Q., Coauthors, 2010: Spatial distributions of particle number concentrations in the global troposphere: Simulations,observations, and implications for nucleation mechanism.J. Geophys. Res.,115,D17205,[1] Particle number concentration in the troposphere is an important parameter controlling the climate and health impacts of atmospheric aerosols. We show that nucleation rates and total particle number concentrations in the troposphere, predicted by different nucleation schemes, differ significantly. Our extensive comparisons of simulated results with land-, ship-, and aircraft-based measurements indicate that, among six widely used nucleation schemes involving sulfuric acid, only the ion-mediated nucleation (IMN) scheme can reasonably account for both absolute values (within a factor of 0908042) and spatial distributions of particle number concentrations in the whole troposphere. Binary homogeneous nucleation (BHN) schemes significantly underpredict particle number concentration in the lower troposphere (below 090804500 mbar), especially in the boundary layer over major continents (by a factor of up to 09080410). BHN is also insignificant in the upper troposphere based on a recent kinetically self-consistent nucleation model constrained by multiple independent laboratory data. Previous conclusions about the importance of BHN in the upper troposphere should be revisited. Empirical activation and kinetic nucleation formulas significantly overpredict the particle number concentrations over tropical and subtropical oceans (by a factor of up to 09080410 in the boundary layer), and the overpredictions extend from ocean surface to around 090804400 mbar. This study represents the first comprehensive comparison of global particle number simulations with relevant measurements that have a 3-D global spatial coverage. Our results suggest that ion-mediated H2SO4-H2O nucleation appears to dominate over neutral H2SO4-H2O nucleation, not only in the lower troposphere but also in the middle and upper troposphere.
    Yue, D. L., Coauthors, 2010: The roles of sulfuric acid in new particle formation and growth in the mega-city of Beijing.Atmos. Chem. Phys.10,4953-4960, measurements of gaseous sulfuric acid and particle number size distributions were performed to investigate aerosol nucleation and growth during CAREBeijing-2008. The analysis of the measured aerosols and sulfuric acid with an aerosol dynamic model shows the dominant role of sulfuric acid in new particle formation (NPF) process but also in the subsequent growth in Beijing. Based on the data of twelve NPF events, the average formation rates (213 cmlt;supgt;amp;minus;3lt;/supgt; slt;supgt;amp;minus;1lt;/supgt;) show a linear correlation with the sulfuric acid concentrations (lt;igt;Rlt;/igt;lt;supgt;2lt;/supgt;=0.85). Coagulation seems to play a significant role in reducing the number concentration of nucleation mode particles with the ratio of the coagulation loss to formation rate being 0.41amp;plusmn;0.16. The apparent growth rates vary from 3 to 11 nm hlt;supgt;amp;minus;1lt;/supgt;. Condensation of sulfuric acid and its subsequent neutralization by ammonia and coagulation contribute to the apparent particle growth on average 45amp;plusmn;18% and 34amp;plusmn;17%, respectively. The 30% higher concentration of sulfate than organic compounds in particles during the seven sulfur-rich NPF events but 20% lower concentration of sulfate during the five sulfur-poor type suggest that organic compounds are an important contributor to the growth of the freshly nucleated particles, especially during the sulfur-poor cases.
    Zhang L. M., S. L. Gong, J. Padro, and L. Barrie, 2001: A size-segregated particle dry deposition scheme for an atmospheric aerosol module.Atmos. Environ.35(3),549-560, 5.10.1016/S0967-0661(00) parameterization of particle dry deposition has been developed fur the Canadian Aerosol Module (CAM). This parameterization calculates particle dry deposition velocities as a function of particle size and density as well as relevant meteorological variables. It includes deposition processes. such as, turbulent transfer, Brownian diffusion. impaction, interception, gravitational settling and particle rebound. Particle growth under humid conditions is also considered. Sensitivity tests show that the parameterization provides deposition velocities comparable with recent field observations, especially for sub-micron particles. The present parameterization has also been evaluated using two empirical bulk resistance models, which were originally developed from field observations. The present parameterization has been implemented in CAM, with meteorological input provided by the Canadian Regional Climate Model (RCM) to the eastern North America. A comparison of the modelled dry deposition velocities to a variety of recent measurements that have been reported in the literature demonstrated that the current parameterization produces reasonable results. The main improvement of the current parameterization compared to earlier size-dependent particle dry deposition models is that the current one produces more realistic deposition velocities for sub-micron particles and agrees better with recently published field measurements. (C) 2000 Elsevier Science Ltd. All rights reserved. [References: 49]
    Zhang Y. M., X. Y. Zhang, J. Y. Sun, W. L. Lin, S. L. Gong, X. J. Shen, and S. Yang, 2011: Characterization of new particle and secondary aerosol formation during summertime in Beijing,China.Tellus B,63,382-394, aerosol number and mass concentrations and the mixing ratios of O3 and various trace gases were continuously measured at an urban station before and during the Beijing Olympic and Paralympic Games (5 June to 22 September, 2008). 23 new particle formation (NPF) events were identified; these usually were associated with changes in wind direction and/or rising concentrations of gas-phase precursors or after precipitation events. Most of the NPF events started in the morning and continued to noon as particles in the nucleation mode grew into the Aitken mode. From noon to midnight, the aerosols grew into the accumulation mode through condensation and coagulation. Ozone showed a gradual rise starting around 10:00 local time, reached its peak around 15:00 and then declined as the organics increased. The dominant new particle species were organics (40-75% of PM1) and sulphate; nitrate and ammonium were more minor contributors.
    Zhao C. F., S. A. Klein, S. C. Xie, X. H. Liu, J. S. Boyle, and Y. Y. Zhang, 2012: Aerosol first indirect effects on non-precipitating low-level liquid cloud properties as simulated by CAM5 at ARM sites.Geophys. Res. Lett.,39,L08806, quantitatively examine the aerosol first indirect effects (FIE) for non-precipitating low-level single-layer liquid phase clouds simulated by the Community Atmospheric Model version 5 (CAM5) running in the weather forecast mode at three DOE Atmospheric Radiation Measurement (ARM) sites. The FIE is quantified in terms of a relative change in cloud droplet effective radius for a relative change in accumulation mode aerosol number concentration under conditions of fixed liquid water content (LWC). CAM5 simulates aerosol-cloud interactions reasonably well for this specific cloud type, and the simulated FIE is consistent with the long-term observations at the examined locations. The FIE in CAM5 generally decreases with LWC at coastal ARM sites, and is larger by using cloud condensation nuclei rather than accumulation mode aerosol number concentration as the choice of aerosol amount. However, it has no significant variations with location and has no systematic strong seasonal variations at examined ARM sites.
    Zhu, Y., Coauthors, 2016: Distribution and sources of air pollutants in the North China plain based on on-road mobile measurements.Atmos. Chem. Phys.16,12 551-12 565, North China Plain (NCP) has been experiencing severe air pollution problems with rapid economic growth and urbanisation. Many field and model studies have examined the distribution of air pollutants in the NCP, but convincing results have not been achieved, mainly due to a lack of direct measurements of pollutants over large areas. Here, we employed a mobile laboratory to observe the main air pollutants in a large part of the NCP from 11 June to 15 July 2013. High median concentrations of sulfur dioxide (SO2) (12 ppb), nitrogen oxides (NOx) (NO+NO2; 452 ppb), carbon monoxide (CO) (956ppb), black carbon (BC; 5.5gm-3) and ultrafine particles (28 350cm-3) were measured. Most of the high values, i.e. 95 percentile concentrations, were distributed near large cities, suggesting the influence of local emissions. In addition, we analysed the regional transport of SO2 and CO, relatively long-lived pollutants, based on our mobile observations together with wind field and satellite data analyses. Our results suggested that, for border areas of the NCP, wind from outside this area would have a diluting effect on pollutants, while south winds would bring in pollutants that have accumulated during transport through other parts of the NCP. For the central NCP, the concentrations of pollutants were likely to remain at high levels, partly due to the influence of regional transport by prevalent south.north winds over the NCP and partly by local emissions.
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Manuscript History

Manuscript received: 29 March 2017
Manuscript revised: 01 August 2017
Manuscript accepted: 14 August 2017
通讯作者: 陈斌,
  • 1. 

    沈阳化工大学材料科学与工程学院 沈阳 110142

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Growth Rates of Fine Aerosol Particles at a Site near Beijing in June 2013

  • 1. State Key Laboratory of Earth Surface Processes and Resource Ecology, and College of Global Change and Earth System Science, Beijing Normal University, Beijing 100875, China
  • 2. Joint Center for Global Change Studies, Beijing 100875, China
  • 3. Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100875, China

Abstract: Growth of fine aerosol particles is investigated during the Aerosol-CCN-Cloud Closure Experiment campaign in June 2013 at an urban site near Beijing. Analyses show a high frequency (∼ 50%) of fine aerosol particle growth events, and show that the growth rates range from 2.1 to 6.5 nm h-1 with a mean value of ∼ 5.1 nm h-1. A review of previous studies indicates that at least four mechanisms can affect the growth of fine aerosol particles: vapor condensation, intramodal coagulation, extramodal coagulation, and multi-phase chemical reaction. At the initial stage of fine aerosol particle growth, condensational growth usually plays a major role and coagulation efficiency generally increases with particle sizes. An overview of previous studies shows higher growth rates over megacity, urban and boreal forest regions than over rural and oceanic regions. This is most likely due to the higher condensational vapor, which can cause strong condensational growth of fine aerosol particles. Associated with these multiple factors of influence, there are large uncertainties for the aerosol particle growth rates, even at the same location.

摘要: 利用北京附近香河站点2013年6月开展的大型综合观测实验(气溶胶-云凝结核-云闭合实验)数据, 本文研究了气溶胶细颗粒物的增长速率. 分析发现该地区细颗粒增长事件出现频率可以高达50%以上, 增长速率介于2.1至6.5 nm/h, 平均增长速率大约5.1 nm/h. 综合前人研究, 我们发现至少有4种机制可以影响细颗粒物的增长: 气态前体物浓度, 模内凝固, 模外凝固和多相化学反应. 在细粒子增长的初始阶段, 凝结增长起着主导作用; 随着粒子的增长, 凝固效率会增强. 对多个不同区域细粒子增长进行总结发现, 细粒子增长速率在大城市, 城区和森林区域要高于乡村和海洋区域. 很大一个原因是大城市, 城区和森林区域的气态前体物浓度高, 使得该地区细颗粒具有很强的凝结增长. 但同时由于影响细颗粒增长的因子较多, 细颗粒凝结增长速率具有较大的不确定性, 变化幅度较大, 即使是在相同地区.

1. Introduction
  • Aerosol is ubiquitous in Earth's atmosphere and causes considerable impacts to society, including changes in climate, atmospheric chemistry and human health (IPCC, 2007). Fine aerosol particles have strong negative effects on atmospheric visibility and human health by entering the respiratory, circulatory and nervous systems (Harrison and Yin, 2000; Kreyling et al., 2004). The climate impact of aerosol is one of the largest uncertainties in current climate model simulations (IPCC, 2007), and atmospheric particle formation has been identified as one of the most important aerosol processes that should be explicitly treated in next-generation climate models (Ghan and Schwartz, 2007). Many studies have focused on both the formation and growth of fine aerosol particles (Kulmala et al., 2004a, 2012; Spracklen et al., 2006, 2010; Yu et al., 2010).

    While aerosol particle formation and growth events can be identified based on the evolution of size distributions and particle number concentrations following the definition of (Kulmala et al., 2004a), their quantitative observation requires measurements of aerosol particle size distributions down to sizes as small as 3 nm in diameter (McMurry, 2000). Actually, even 3 nm is not small enough to study the aerosol formation process, which is mainly the nucleation process (Kulmala et al., 2004b). Therefore, using aerosol measurements from differential mobility particle sizer or scanning mobility particle sizer (SMPS) systems with a cutoff size of 3 nm or even larger, is not suitable for the detection of nucleation and the initial steps of particle growth (Kulmala et al., 2004b). In this paper, we only examine the growth of atmospheric fine aerosol with a size range of 10-100 nm without considering the formation process.

    The growth of atmospheric fine aerosol particles is a frequent global phenomenon, and one of the major sources for accumulation-mode (0.1-2.0 μm) aerosol particles in both clean and polluted atmospheres. When fine aerosol particles grow large enough to serve as cloud condensation nuclei (CCN), they modify Earth's radiation budget by reflecting solar radiation directly or indirectly, e.g. via cloud albedo (Twomey, 1974; Garrett and Zhao, 2006; Lubin and Vogelmann, 2006; Spracklen et al., 2008; Zhao et al., 2012), cloud lifetime (Albrecht, 1989), or cloud invigoration (Rosenfeld et al., 2008; Li et al., 2011). Thus, it is important to study the growth of fine aerosol particles.

    In recent times, Beijing has continuously experienced many heavy haze events almost every year, and vehicle emissions through secondary aerosol formation have become one of the major sources of atmospheric pollution in city. It is therefore important for us to know the frequency of fine aerosol particle growth events and understand the growth rate (GR) of fine aerosol particles.

    In this study, we examine the GRs of fine aerosol particles near Beijing based on 10 fine aerosol particle growth events found during a field experiment in June 2013. We then try to understand the different GRs over several locations found by various studies.

2. Field experiment
  • A comprehensive intensive observation period field experiment concerning aerosol and clouds, called the Aerosol-CCN-Cloud Closure Experiment (AC3E), was carried out during 1-30 June 2013 at Xianghe (39.80°N, 116.96°E; 35 m above sea level) in Hebei Province, China, located about 60 km southeast of Beijing. Figure 1 shows the location of the site. It lies in a plain area surrounded by agricultural land, densely occupied residences, and light industry. Situated close to the local downtown area with a population of 50 000 and between two megacities (Beijing and Tianjin), the site experiences frequent pollution plumes deriving from urban, rural or mixed origin.

    AC3E provided a series of observations such as aerosol particle size distribution, mass distribution, chemical composition, cloud condensation nuclei and meteorological status. The present study mainly uses the measurements of aerosol particle size distribution and particle chemical composition. Aerosol particle size distribution (10-500 nm) is measured with TSI's SMPS 3082. Before entering the instrument, the air flow is dried with a silica gel diffusion dryer to an average relative humidity of < 5%. The measurements of non-refractory submicron (40 nm to 1 μm) aerosol species including organics, sulfate, nitrate, ammonium and chloride are obtained with an Aerodyne Aerosol Chemical Speciation Monitor (Sun et al., 2012). Detailed descriptions of these instruments can be obtained from the instrument manuals and corresponding references (e.g. Sun et al., 2012). CCN data, which are obtained at supersaturations of 0.2%, 0.5% and 0.8% using a Droplet Measurement Technologies continuous-flow CCN counter (Lance et al., 2006), are also used in this study to examine the impact of fine aerosol particle growth.

    Figure 1.  Location of the site at Xianghe, where we carried out the AC3E campaign field measurements.

    The meteorological conditions were recorded during the campaign. For most cases, the weather was hot and wet, with an average temperature of 23.6°C and an average ambient relative humidity of 72.3%.

3. Theory and method
  • Although not the focus of our study, we begin by providing a brief summary of the mechanisms for fine aerosol particle formation. As shown in (Kulmala et al., 2000), several nucleation mechanisms have been proposed to explain fine aerosol particle production, along with meteorological-related nucleation enhancement processes such as turbulent fluctuations, waves and mixing (Easter and Peters, 1994; Nilsson and Kulmala, 1998). Two fine aerosol particle formation theories——binary nucleation theory (water and sulfuric acid) (Doyle, 1961; Raes et al., 1992; Kulmala et al., 1998) and ternary nucleation theory (sulphuric acid-ammonia-water) (Coffman and Hegg, 1995; Korhonen et al., 1999)——have indicated the importance of sulfuric acid and ammonia to the formation of fine aerosol particles.

    Figure 2.  An example of a fine aerosol particle growth event that occurred on 17 June 2013.

    Our focus is the growth of fine aerosol particles. As shown in Table 1, several mechanisms for fine aerosol particle growth have been proposed by (Kulmala et al., 2004b). The study indicated that the first, third and fourth mechanisms shown in Table 1 do not require additional vapors other than those participating in the nucleation processes (which are the major mechanisms for fine aerosol particle formation), whereas the other two mechanisms do. In general, condensational growth associated with mechanisms 1-3 is more significant when concentrations of condensable vapors are higher, and the efficiency of these three mechanisms should decrease with growth time and then particle sizes due to the consumption of condensable vapors; self-coagulation efficiency increases with sizes during the aerosol growing stage; and multi-phase chemical reactions are favored by an acidic environment. Recently, (Yue et al., 2010) indicated that fine aerosol particle growth process is mainly caused by three mechanisms: intramodal coagulation, extramodal coagulation with larger pre-existing particles, and vapor condensation. Different from (Kulmala et al., 2004b), (Yue et al., 2010) indicated negative effects of extramodal coagulation for the growth of fine aerosol particles: the growing aerosol particles can be scavenged or removed by pre-existing larger particles. We should note that many studies (e.g., Kulmala et al., 2005; Kuang et al., 2012) show the primary mechanism for the growth of fine aerosol particles is the condensation of sulfuric acid vapor and low-volatility organic vapors. In summary, the growth of fine aerosol particles should be strongly associated with the condensation of sulfuric acid vapor and low-volatibility organic vapors, the concentration of pre-existing large size aerosol, the concentration of fine aerosol particles, and favorable meteorological conditions.

  • Fine aerosol particle growth events are identified in this study based on the evolution of aerosol particle size distributions following the definition of (Kulmala et al., 2004a). Specifically, an obvious growth trend in particle size distributions can be found during fine aerosol particle growth events.

    Following the expression in (Heintzenberg, 1994), GR is defined as the growth rate of fine aerosol particles at mean diameter D m within a time period ∆ t: \begin{equation} \label{eq1} {\rm GR}=\frac{\Delta D_{\rm m}}{\Delta t} .\ \ (1) \end{equation} Note that the mean diameter D m is a mean geometric diameter of a log-normal ultrafine aerosol particle mode, which has been fitted to the number size distribution. GR can also be expressed as (Kulmala et al., 1998) \begin{equation} \label{eq2} \frac{dD_{\rm p}}{dt}=\frac{4m_{\upsilon}\beta_{\rm M}DC}{\rho D_{\rm p}} , \ \ (2)\end{equation} where D p is the particle radius, \(m_\upsilon\) is the molecular mass of condensable vapor, D is the diffusion coefficient, C is the vapor concentration, ρ is the particle density, and β M is the transitional correction factor for the mass flux. Equation (3) shows that GR should be related to condensable vapor, particle size and particle concentration. As indicated earlier, both condensation and coagulation play important roles for fine aerosol particle growth.

    Figure 2 shows the temporal variation of aerosol particle size distribution and total aerosol number concentration in the size range from 10 nm to 500 nm on 17 June 2013. Based on the identification method described above, a fine aerosol particle growth event occurs on this day. The aerosol number concentration shows a sharp increase in the initial stage (1100-1400 LST) of this growth event due to the conversion of fine aerosol from sizes below 10 nm to above 10 nm. Considering the two facts that the aerosol number concentration does not change much in the initial stage (such as 10-50 nm) and there are generally heavy emissions of NOx and SO2 gases from strong traffic pollution and burning coal in this region, the fast growth of fine aerosol particles in the initial stage should be associated with condensational growth, as shown in Eq. (3). In the later stage, the aerosol number concentration decreases gradually, which should be due to intramodal and extramodal coagulations. Interestingly, there is a jump in aerosol number concentration between 1900 and 2100 LST, which should be due to the aerosol particles from other sources such as biomass burning. For the measured size range between 10 and 500 nm, there is a clear increasing trend in aerosol particle sizes with time during 1100-2200 LST. It is highly likely that new aerosol particle formation occurs at times before 1100 LST, such as 0900-1100 LST, which is consistent with the findings of many other studies (e.g., Wu et al., 2007; Zhang et al., 2011).

    Figure 3.  Temporal variation of particle number size distribution between 10 nm and 500 nm and aerosol number concentration with sizes larger than 25 nm (green line), 50 nm (blue line), and 100 nm (purple line), for the AC3E campaign period of 9-25 June 2013.

    Figure 3 illustrates the calculation of GR using Eq. (2) for fine aerosol particles measured at Xianghe on 17 June 2013. Using the time series data of aerosol particle size distributions, ∆ D m and ∆ t can be easily estimated. The fine aerosol particle GRis slightly larger for the period 1100-1430 LST than for 1430-1800 LST, which could be associated with the decreasing condensation efficiency and increasing extramodal coagulation efficiency while the intramodal coagulation efficiency also increases. After 1800 LST, the GR becomes a little larger again. Roughly estimated, the mean particle size increases from 25 nm to 100 nm from 1100 to 2230 LST, corresponding to a mean GR of 6.5 nm h-1.

    Large uncertainties in the estimations of GR could exist. As indicated by (Kulmala et al., 2004a), the main problem for GR calculation is to distinguish between fine mode and pre-existing large aerosol particles. The GR is defined as the slope of the linear fitting line between aerosol particle mean size and time. However, different from that shown in (Shi and Qian, 2003), the mean sizes of fine aerosol particles usually do not show a perfect positive linear relation with time because of two issues. One is the existence of large sized background aerosol particles, and the other is the fluctuation of the particle size distributions. Both make it difficult to identify the size classes that belong to the fine aerosol particle growth events. Unless it is very clear, we need to make a good guess based on our knowledge. Sometimes, it is even difficult to give an accurate estimate for the start and end points of fine aerosol particle growth events, which usually also affects the calculation of the fine aerosol particle GR. Considering these factors of influence, uncertainties in determined GRs are also examined in this study. For example, the uncertainty for the determined GR values in Fig. 3 is estimated as 0.8 nm h-1.

    The observed particle size distributions can be classified into three modes: "nucleation mode", with size D m≤ 25 nm; "Aitken mode", with a size range of 25-100 nm; and "accumulation mode", with size range of 100-1000 nm. The nucleation mode and Aitken mode aerosol particle GRs are generally different. Considering the aerosol size range measured here is between 10 and 500 nm, the average GRs of fine aerosol particles in the size range of 10-100 nm are examined with Eq. (2) in this study.

4. Results and discussion
  • Figure 4 shows the temporal variation of measured aerosol size spectra between 10 and 500 nm during the AC3E campaign period of 9-25 June 2013, except 18 June when an instrument error occurred. While not always obvious, fine aerosol particle growth events occur on days 9, 10, 11, 12, 13, 17, 19, 20, 21 and 23. The frequency of days that fine aerosol particle growth events occur is around 50%. Assuming these fine aerosol particles are formed locally, the occurrence frequency of fine aerosol growth events is much larger than that found by (Wu et al., 2007) and (Shen et al., 2011), which show about 20% and 12% respectively in summer. Note that (Wu et al., 2007) and (Shen et al., 2011) used SMPS measurements with a lower size limit of 3 nm, and what they determined were frequencies of new particle formation events that occurred in years other than 2013. Also, Xianghe is a little farther away from central Beijing. Consistent with most studies (e.g., Kulmala et al., 2004a; Wu et al., 2007), fine aerosol particle growth events often occur on clean and sunny days, and the particles can grow large enough as accumulation mode aerosol in several hours or 1-2 days. Most of these fine aerosol particle growth events observed here typically begin around 0900-1200 LST, which is consistent with (Zhang et al., 2011) and (Wu et al., 2007).

    Figure 4.  An example of the calculation of GR on 17 June 2013.

    Figure 4 shows the temporal variation of aerosol number concentration with sizes larger than 25 nm, 50 nm and 100 nm separately, which exactly illustrates this point. Aerosol with sizes larger than 100 nm (accumulation-mode aerosol) can be treated as pre-existing large sized background aerosol in the initial stage of a fine aerosol particle growth event, which is generally minimal in concentration during the day of the growth event. Thus, we can use the daily minimum aerosol concentration in the accumulation mode to estimate the relative impact caused by extramodal coagulation on the mean growth rate of fine aerosol particles in an event. Unfortunately, there is no clear relationship between the daily minimum accumulation-mode aerosol concentrations and the GRs of fine aerosol particles, as shown in Fig. 4. This may imply a deficiency of extramodal coagulation.

    For all fine aerosol particle growth event days during the AC3E campaign, the GRs are calculated and shown in Fig. 5. The GR values range from 2.1 to 6.5 nm h-1, with an average value around 5.1 nm h-1. These values are roughly consistent with the findings from previous studies in the Beijing area (Wu et al., 2007; Yue et al., 2010; Zhang et al., 2011), which show averaged GRs of about 3-5 nm h-1. However, as indicated in Fig. 4, large uncertainties exist for determined fine aerosol particle GRs at each event, which is usually about 0.5-1 nm h-1.

    Figure 5.  Temporal variation of aerosol chemical composition measured during the AC3E campaign between 9 and 25 in June 2013.

    Figure 6 shows that the dominant aerosol chemical compositions are organics and nitrate, with relatively smaller amounts of ammonium and sulfate, which is slightly different from the findings of (Zhang et al., 2011) in which the amount of sulfate was more than that of nitrate. Note that the chemical composition from the Aerosol Chemical Speciation Monitor (ACSM) in Fig. 6 is for aerosol particles with sizes between 40 nm and 1 μm. Here, we simply assume that the particles with sizes between 10 and 500 nm measured by SMPS have the same chemical composition as obtained by ACSM. The NOx and SO2 gases are emitted mainly from strong traffic pollution and burning coal (Zhu et al., 2016), which serve as precursors of fine aerosol particles and provide an acidic environment that can cause fast growth of fine aerosol particles through vapor condensation. As shown in Zhu et al. (2016, Figs. 2 and 3), both observation and model simulation results for a short period during the observation window show high concentrations of NOx and SO2, at roughly 400 ppb and 25 ppb, respectively. These help make the growth of fine aerosol particles faster. Also, the acidic environment strengthens the multi-phase chemical reactions such that fine aerosol particles can grow faster.

    Figure 6.  Growth rates of fine aerosol particles for observed events during the AC3E campaign between 9 and 25 June 2013. The circles represent the mean values and the bars represent the ranges.

    Figure 7.  Temporal variation of CCN concentration at supersaturations of 0.2%, 0.5% and 0.8% during the AC3E campaign between 9 and 25 June 2013.

    One important point regarding the growth of fine aerosol particles is that large aerosols play important indirect radiative roles by serving as CCN. Figure 7 shows the temporal variation of CCN during the AC3E campaign. For almost every fine aerosol growth event, the concentration of CCN is lowest in the initial stage, and quickly increases with the growth of the fine aerosol particles. When the aerosol particles grow large enough, the intramodal and extramodal coagulations make the CCN number concentration decrease. From Fig. 7, we can also identify the main growth trends as found in Fig. 4: a significant increase in CCN on the days when fine aerosol particles grow. When the environment is suitable for cloud formation, increased CCN will have strong impacts on both cloud microphysical properties and radiation budgets.

  • By combining various findings on the GRs of fine aerosol particles at different locations, we can examine the spatial variation of GRs. Table 2 lists the fine aerosol particle GRs found by various studies over six different types of locations: clean Antarctic region, slightly polluted rural areas, polluted urban areas, relatively clean (or lightly polluted) megacities, polluted megacities, and boreal forest. The reference studies, locations, and growth rates obtained are also listed in the table. Note that there are strong seasonal variations for fine aerosol particle GRs found by many of these previous studies. Higher GRs of fine aerosol particles are found during summer than in winter, which is potentially associated with the higher precipitable water vapor concentration in summer. Based on the studies listed in Table 2, we provide a rough estimate of the mean GR of fine aerosol particles over each location. These are: 0.2, 1.3, 3.8, 5.0, 2.0 and 5.0 nm h-1, for the Antarctic, rural, urban, polluted megacity, relatively clean megacity, and boreal forest, respectively. Note that these estimates are very rough and large uncertainties could exist.

    Figure 8 shows the variation in mean GRs over the six locations indicated in Table 2. The bars represent the potential ranges of fine aerosol particle GRs and the red lines indicate the estimated mean values of GRs for the corresponding location types. In general, the fine aerosol particle GRs have a large variability, even in the same location type dominated by similar aerosol types. This suggests significant influences from other environmental factors such as meteorological conditions and pre-existing background aerosol pollution. These results presented in section 3 imply that one dominant mechanism for the variation of GRs with location is vapor condensation. Both fine aerosol particle GRs and condensable vapor concentration are larger in urban and polluted megacity regions compared with Antarctic and rural regions. For relatively clean megacities, the fine aerosol particle GRs lie between those of urban and rural regions. Due to the release of volatile organic compounds from boreal regions, the mean fine aerosol particle GR over boreal forest is also large——almost the same as that over polluted megacities. In addition, multi-phase chemical reactions are generally larger in the urban, megacity and boreal regions.

    Figure 8.  Variation of fine aerosol particle growth rates with location [clean Antarctic, clean rural, urban, and megacities (divided into clean and polluted), and forest]. The results are from different studies shown in Table 1. The bars represent the most likely ranges and the red lines indicate the mean values of GRs for the corresponding location types.

5. Summary and discussion
  • The growth of fine aerosol particles is a frequent phenomenon in Earth's atmosphere and plays an important role for local environments and global climate change. Based on short-term aerosol observations during the AC3E campaign, the present study shows a high frequency (∼50%) of fine aerosol particle growth events at Xianghe in summer. The GRs of fine aerosol particles during the AC3E campaign range from 2.1 to 6.5 nm h-1, with a mean value of ∼ 5.1 nm h-1. The most likely contribution to the GRs of fine aerosol particles from four factors of influence are discussed in this study, including vapor condensation, intramodal coagulation, extramodal coagulation and multi-phase chemical reactions. For Xianghe, with its heavy releases of organic, nitrate and sulfate materials (Zhu et al., 2016), vapor condensation should play a major role for the growth of fine aerosol in the initial stage, making GRs high. Considering the several mechanisms for fine aerosol particle growth proposed by (Kulmala et al., 2004b) and (Yue et al., 2010), in the following stages, the combined impacts of extramodal and intramodal coagulations should contribute to the growth of fine aerosol particles, along with condensation growth. Due to the existence of pre-existing large size aerosol particles and the fluctuations of aerosol size distributions (such as on 19, 20 and 21 June in Fig. 4), large uncertainties could exist for our calculated GRs of fine aerosol.

    A review of previous findings about the GRs of fine aerosol particles shows higher GR values over megacity, urban and boreal forest regions compared with rural or oceanic regions, most likely caused by the more significant vapor condensation effects. The heavy releases of organic, nitrate and sulfate materials in urban and megacity regions, and the heavy releases of volatile organic compounds from boreal forest regions, make the condensational vapor in megacity, urban and boreal forest regions much greater than in rural or oceanic regions. In short, GRs of fine aerosol particles are influenced by multiple factors including condensational vapor, pre-existing large aerosol particles, and various other environmental factors, causing observed values to vary within a broad range and with large uncertainties, even over the same location.

    This study uses theories and results from previous studies to explain our observational findings for the fast GRs (2.1-6.5 nm h-1) of fine aerosol particles found at Xianghe near Beijing, which include both the condensational growth and coalescence growth of fine aerosol particles. Whilst carried out in some of the studies cited here, model simulations or lab investigations have not been carried out to further evaluate our explanation, which would be a valuable approach to take in the future. Moreover, this study calculates the GRs of fine aerosol particles without considering their dissipation through dry deposition, while precipitation scavenging or wet deposition has been excluded. The dry deposition may have slightly increased the calculated GRs since it is easier for smaller particles to be deposited at the growth size range between 10 and 500 nm (Zhang et al., 2001). In other words, the GRs of fine aerosol particles could be slightly smaller in the study area.




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