Andronache C., 2004: Estimates of sulfate aerosol wet scavenging coefficient for locations in the Eastern United States. Atmos. Environ., 38( 6), 795- 804.10.1016/ of atmospheric aerosols by falling precipitation is a major removal mechanism for airborne particles. The process can be described by a wet scavenging coefficient (WSC), denoted L , that is dependent on the rainfall rate, R , and the collision efficiency between raindrops and aerosol particles, E . We report bulk average L values for location in the Eastern United States, estimated based on sulfate mass balance in the atmospheric domain of interest. Data used are taken from several observational networks: (a) the Atmospheric Integrated Research Monitoring Network (AIRMoN) which is part of the National Atmospheric Deposition Program/National Trends Network (NADP/NTN); (b) the Interagency Monitoring of Protected Visibility Environments (IMPROVE); and (c) the National Climatic Data Center (NCDC). The results are fitted relatively well by L values computed using a microphysical representation of the WSC process based on collision efficiency and precipitation size distribution. Such representation leads to a simple expression L = f ( R ) for soluble aerosols, suitable for WSC description in regional scale models. The agreement between the bulk method and the microphysical representation is due in part to the predominant widespread precipitation, well represented by Marshall and Palmer raindrop distribution, and in part due to assumptions made in the bulk model. Results indicate that high-resolution rainfall rates and realistic vertical cloud structure information are needed to improve the accuracy of aerosol wet scavenging modeling for pollution studies.
Belosi F., D. Contini, A. Donateo, G. Santachiara, and F. Prodi, 2012: Aerosol size distribution at Nansen Ice Sheet Antarctica. Atmos. Res., 107, 42- 50.10.1016/ austral summer 2006, in the framework of the XXII Italian Antarctic expedition of PNRA (Italian National Program for Research in Antarctica), aerosol particle number size distribution measurements were performed in the 10-500 range nm over the Nansen Ice Sheet glacier (NIS, 74°30' S, 163°27' E; 85 m a.s.l), a permanently iced branch of the Ross Sea. Observed total particle number concentrations varied between 169 and 1385 cm. A monomodal number size distribution, peaking at about 70 nm with no variation during the day, was observed for continental air mass, high wind speed and low relative humidity. Trimodal number size distributions were also observed, in agreement with measurements performed at Aboa station, which is located on the opposite side of the Antarctic continent to the NIS. In this case new particle formation, with subsequent particle growth up to about 30 nm, was observed even if not associated with maritime air masses.
Berthet S., M. Leriche, J.-P. Pinty, J. Cuesta, and G. Pigeon, 2010: Scavenging of aerosol particles by rain in a cloud resolving model. Atmos. Res., 96, 325- 336.10.1016/ describe a below-cloud scavenging module of aerosol particles by raindrops for use in a three-dimensional mesoscale cloud resolving model. The rate of particle removal is computed by integrating the scavenging efficiency over the aerosol particle and the drop size distributions. Here the numerical integration is performed accurately with a Gauss quadrature algorithm. The efficiency of the scavenging module is partially confirmed with experimental data. More interestingly, it is illustrated by two numerical experiments: the simulation of a forced convective circulation in a tropical cloudy boundary layer and a two-dimensional simulation of an African squall line. The results show a very selective wet removal of the aerosol particles which clearly depends on the mode radius, the width and the vertical profile of concentration. Furthermore, the squall line case shows the importance of resolving internal circulations to redistribute layers of aerosol particles in order to improve estimates of particle removal by below-cloud scavenging.
Charlson R. J., S. E. Schwartz, J. M. Hales, R. D. Cess, J. A. Coakley Jr., J. E. Hansen, and D. J. Hofmann, 1992: Climate forcing by anthropogenic aerosols. Science, 255, 423- 430.10.1126/ long considered to be of marginal importance to global climate change, tropospheric aerosol contributes substantially to radiative forcing, and anthropogenic sulfate aerosol in particular has imposed a major perturbation to this forcing. Both the direct scattering of short-wavelength solar radiation and the modification of the shortwave reflective properties of clouds by sulfate aerosol particles increase planetary albedo, thereby exerting a cooling influence on the planet. Current climate forcing due to anthropogenic sulfate is estimated to be -1 to -2 watts per square meter, globally averaged. This perturbation is comparable in magnitude to current anthropogenic greenhouse gas forcing but opposite in sign. Thus, the aerosol forcing has likely offset global greenhouse warming to a substantial degree. However, differences in geographical and seasonal distributions of these forcings preclude any simple compensation. Aerosol effects must be taken into account in evaluating anthropogenic influences on past, current, and projected future climate and in formulating policy regarding controls on emission of greenhouse gases and sulfur dioxide. Resolution of such policy issues requires integrated research on the magnitude and geographical distribution of aerosol climate forcing and on the controlling chemical and physical processes.
Chate D. M., 2005: Study of scavenging of submicron-sized aerosol particles by thunderstorm rain events. Atmos. Environ., 39, 6608- 6619.10.1016/ scavenging coefficients for 0.013–0.75μm particles are between 1.08×10 615 and 7.58×10 614 s 611 . Based on observed results a correlation between scavenging coefficient and rain intensity is obtained to study below thundercloud scavenging of atmospheric aerosols during thunderstorm rain events. When the rain intensity increases from 5.24 to 45.54mmh 611 , the corresponding scavenging coefficient increases from 0.5×10 615 to 4×10 615 s 611 for thunderstorm rain episodes. The overall scavenging coefficients for 0.02 – 10μm particles at different rainfall rates are estimated from contributions of Brownian diffusion, directional interception, inertial impaction, thermophoresis, diffusiophoresis and electrical forces during thunderstorms. The evolutions of PSD are predicted at different time intervals with theoretical scavenging rates. Comparison of observed evolutions of PSD during thunderstorm rain events with predicted evolutions of PSD shows an order of discrepancy between the observed and model results. Possible causes for discrepancy are discussed in terms of uncertainties in observed data and shortcomings in theoretical approach. The present results are useful for recommendations for the type of experimental setup essential for the field study of precipitation scavenging and improvements in theoretical approach close to atmospheric conditions during thunderstorm rain events.
Chate D. M., P. S. P. Rao, M. S. Naik, G. A. Momin, P. D. Safai, and K. Ali, 2003: Scavenging of aerosols and their chemical species by rain. Atmos. Environ., 37( 18), 2477- 2484.10.1016/S1352-2310(03) or scavenging coefficients have been widely used to study the wet deposition processes quantitatively. In the present theoretical study, the washout coefficients are computed for the aerosols of diameters in the range of 0.02-10 渭m having various densities in accordance with their chemical compositions for heavy rain regime. The theoretical scavenging rates are applied to the observed average particle size distributions of pre-monsoon months of the year 1998 and 1999 for Pune and 1999 for Himalayan regions. The evolution of particle size distributions at different time intervals for the non-hygroscopic particles of CaCO_3, MgCO_3, Zn and Mn indicates that the inertial impaction mechanism is the dominant one in removing particles of all sizes for the heavy rain regime. The size dependence of aerosols as a function of relative humidity is considered for the estimation of washout coefficients of hygroscopic particles such as NaCl and (NH_4)_2SO_4. The washout coefficients are found to be highly dependent on relative humidity for hygroscopic particles. The rainwater concentrations are predicted as a function of rainfall depth and a comparison is made with the observed rainwater concentrations of sequential samples collected on 27 June 2001 in a single rain event to support the results of this theoretical work. The predicted rainwater concentrations for RH = 50% are about two times larger than that for RH = 95% in the case of hygroscopic particles.
Chate D. M., K. Ali, G. A. Momin, P. S. P. Rao, P. S. Praveen, P. D. Safai, and P. C. S. Devara, 2007: Scavenging of sea-salt aerosols by rain events over Arabian Sea during ARMEX. Atmos. Environ., 41, 6739- 6744.10.1016/ coefficients are obtained for sea-salt particles at rainfall intensity of 5, 10, 15, 20 and 45 turn h(-1). Evolutions of size distributions for sea-salt particles by precipitation scavenging are simulated using theoretically estimated scavenging coefficients. Results indicate that below-cloud scavenging affects mainly sea-salt particles in coarse mode. Observed concentrations of Na+ and Cl- in rainwater increased with rainfall intensity and aerosol size. Comparison of predicted concentrations of Na+ and Cl- in rainwater with observed ionic concentrations of short-timed wet-only samples collected during rain events on 2 August 2002 over Arabian Sea (ARMEX-2002) supports the model result. (C) 2007 Elsevier Ltd. All rights reserved.
Chate D. M., P. Murugavel, K. Ali, S. Tiwari, and G. Beig, 2011: Below-cloud rain scavenging of atmospheric aerosols for aerosol deposition models. Atmos. Res., 99, 528-
Croft, B., Coauthors, 2009: Influences of in-cloud aerosol scavenging parameterizations on aerosol concentrations and wet deposition in ECHAM5-HAM. Atmos. Chem. Phys., 9( 5), 22041- 22101.10.5194/ diagnostic cloud nucleation scavenging scheme, which determines stratiform cloud scavenging ratios for both aerosol mass and number distributions, based on cloud droplet, and ice crystal number concentrations, is introduced into the ECHAM5-HAM global climate model. This scheme is coupled with a size-dependent in-cloud impaction scavenging parameterization for both cloud droplet-aerosol, and ice crystal-aerosol collisions. The aerosol mass scavenged in stratiform clouds is found to be primarily (>90%) scavenged by cloud nucleation processes for all aerosol species, except for dust (50%). The aerosol number scavenged is primarily (>90%) attributed to impaction. 99% of this impaction scavenging occurs in clouds with temperatures less than 273 K. Sensitivity studies are presented, which compare aerosol concentrations, burdens, and deposition for a variety of in-cloud scavenging approaches: prescribed fractions, a more computationally expensive prognostic aerosol cloud processing treatment, and the new diagnostic scheme, also with modified assumptions about in-cloud impaction and nucleation scavenging. Our results show that while uncertainties in the representation of in-cloud scavenging processes can lead to differences in the range of 20-30% for the predicted annual, global mean aerosol mass burdens, and near to 50% for accumulation mode aerosol number burden, the differences in predicted aerosol mass concentrations can be up to one order of magnitude, particularly for regions of the middle troposphere with temperatures below 273 K where mixed and ice phase clouds exist. Different parameterizations for impaction scavenging changed the predicted global, annual mean number removal attributed to ice clouds by seven-fold, and the global, annual dust mass removal attributed to impaction by two orders of magnitude. Closer agreement with observations of black carbon profiles from aircraft (increases near to one order of magnitude for mixed phase clouds), mid-troposphere 210Pb vertical profiles, and the geographic distribution of aerosol optical depth is found for the new diagnostic scavenging scheme compared to the prescribed scavenging fraction scheme of the standard ECHAM5-HAM. The diagnostic and prognostic schemes represent the variability of scavenged fractions particularly for submicron size aerosols, and for mixed and ice phase clouds, and are recommended in preference to the prescribed scavenging fractions method.
Duhanyan N., Y. Roustan, 2011: Below-cloud scavenging by rain of atmospheric gases and particulates.. Atmos. Environ, 45, 7201- 7217.10.1016/ scavenging (BCS) by rain is one of the phenomena that control the removal of atmospheric pollutants from air. The present work introduces a detailed review of the most literature referred theories and parameterisations to describe the below-cloud scavenging by rain in air quality modelling. The theories and parameterisations in question concern the raindrop size distribution (RSD), the terminal velocity of raindrops, and the below-cloud scavenging coefficient for gaseous and particulate pollutants. 0D computations are run to calculate the latter coefficient with the help of the current theories and parameterisations thus extracted from the literature. As a result to improve the atmospheric modelling studies, it can be mentioned that the choice of the raindrop terminal velocity among the available parameterisations does not matter much and therefore, the practice of the most simple formulae is advised. On the other hand, a great dispersion on the scavenging coefficient (several orders of magnitude) is observed related to the variations of the RSD. Therefore, a great care is recommended in the choice of the RSD with respect to the type of rain and sampling duration involved (e.g. thunderstorm, widespread, shower, etc.; long or instantaneous sampling duration). Many uncertainties do remain due to the lack of precision in the experimental records after which the RSD parameterisations are established or to the poor level of accuracy of the theoretical models.
Flossmann A. I., H. R. Pruppacher, and J. H. Topalian, 1987: A theoretical study of the wet removal of atmospheric pollutants. Part II: The uptake and redistribution of (NH4) 2SO4 particles and SO2 gas simultaneously scavenged by growing cloud drops. J. Atmos. Sci., 44( 20), 2912- 2923.10.1175/1520-0469(1987)0442.0.CO; A theoretical model has been formulated which allows the processes which control the wet deposition of atmospheric aerosol particles and pollutant gases to be included in cloud dynamic models. The cloud considered in the model was allowed to grow by condensation and collision--coalescence, to remove aerosol particles by nucleation and impaction scavenging, and to remove pollutant gases by convective diffusion. The model was tested by using a simple air-parcel model as the dynamic framework. In this form the model was used to determine the fate of ammonium sulfate ((NHâ)âSOâ) particles and sulfur dioxide (SOâ) gas as they became scavenged by cloud and precipitation drops. Special emphasis was placed on determining 1) the evolution with time of the mass of total sulfur as S(IV) and S(VI) inside the drops, 2) the evolution with time of the acidity of the cloud water as a function of various oxidation rates and as a function of drop size, 3) the relative importance of sulfur scavenging from SOâ as compared to sulfur scavenging from (NHâ)âSOâ particles, and 4) the effect of cloud drop evaporation on the aerosol particle size distribution in the air.
Gon\ccalves, F. L. T., A. M. Ramos, S. Freitas, M. A. S. Dias, O. Massambani, 2002: In-cloud and below-cloud numerical simulation of scavenging processes at Serra Do Mar region, SE Brazil. Atmos. Environ., 36( 33), 5245- 5255.10.1016/S1352-2310(02) scavenging processes have been investigated, taking into consideration a numerical simulation through the model Regional Atmospheric Modeling System (RAMS), the below-cloud scavenging model, local atmospheric conditions and local emissions in the Serra do Mar region in southeastern Brazil. The RAMS modeling was coupled with a one-dimensional (1-D) below-cloud scavenging model in order to simulate the in-cloud and below-cloud scavenging processes. RAMS modeling was also used in order to simulate the cloud structures. The aim of the modeling was to predict the average concentration of three chemical species found in rainwater: SO , NO and NH , scavenged from the atmosphere. The concentrations of gases and particles in the samplings, as well as the meteorological parameters obtained during the March 1993 Campaign, were the input data in both models. Another objective was to compare the modeled and the observed rainwater and determine the variability in concentration. Rainwater was obtained by using fractionated rain samplers. Variability was determined through chemical analysis. Urban and rural aerosol spectra modeling were also used in order to compare the rainwater concentration species variability. When both in-cloud and below-cloud processes are included, the general result of the March 1993 events presents a better agreement between modeled and observed data sets than only below-cloud . Preliminary results lead us to conclude that the rainwater variability of nitrate is explained by the scavenging of particles from urban spectrum size distribution, whereas rural spectra explain ammonium rainwater variability-攊ndicating the different sources of those species. Comparing to the March 1992 events, these case studies present a significant contribution from the in-cloud scavenging, supported by the Weather Radar maps and RAMS modeling. In particular, the almost constant rainwater concentrations on 16 March (an indication of strong in-cloud contribution) are related to the rainfall event, which crossed the study area on that day. These results add an important understanding to the atmospheric wet removal processes in the region studied.
Gon\ccalves, F. L. T., W. N. Morinobu, M. F. Andrade, A. Fornaro, 2007: In-cloud and below-cloud scavenging analysis of sulfate in the metropolitan area of S\ ao Paulo, Brasil. Revista Brasileira De Meteorologia, 22, 94- 104.10.1590/ Metropolitan Area of So Paulo (MASP) is one of the largest urban centers in the world. The significant atmospheric concentrations of ozone, inhalable particles and other pollutants in the MASP raise serious air-quality concerns. In this study, we consider gases, particulate matter (PM) and cloud processes, with a focus on sulfate chemistry. The Regional Atmospheric Modeling System mesoscale numerical model was used in conjunction with detailed scavenging models to compare varying PM mass spectra and size distributions. Field data were collected during the July 1989-May 1990 and February-October 2000 campaigns. Adjusted-urban and rural spectra seem to fit better with observed results which improved the scavenging numerical modeling. Correlations between modeled and observed concentrations were better when the model included rural and adjusted-urban spectra, suggesting locally dominant below-cloud scavenging. Spatial variability analysis and numerical modeling also revealed that the varying sulfate rainwater concentrations indicate below-cloud removal process dominance.
Hu M., J. Zhang, and Z. J. Wu, 2005: Chemical compositions of precipitation and scavenging of particles in Beijing. Science in China Series B: Chemistry, 48, 265- 272.10.1360/ deposition is the scavenging approach of pollutants from the atmosphere. Rain in summer and snow in winter are the main scavenging processes of air pollutants by wet deposition in Beijing and key factors of changing air pollutants concentrations[1].
Jiang Q., Y. Yin, Y. S. Qin, K. Chen, and S. Y. Yang, 2013: Numerical simulation study on hygroscopic growth of aerosols in Huangshan area. Journal of the Meteorological Sciences, 33( 3), 237- 245. (in Chinese) using adiabatic air parcel method of multi-component aerosols,this paper analyzes hygroscopic growth characteristics of aerosols in Huangshan area in 2008.Some calculations show that The hygroscopic growth factor f defined as d p,wet/d p,dry,where d p,wet is the particle mobility diameter under a humidified condition,is closely bound up with particle radius,relative humidity(RH),particle chemical components,vertical velocity and lifting height.The hygroscopic growth of small particles is more significant than that of the large ones.Relative humidity is positively related with the hygroscopic growth factor f.The more relative humidity approaches the critical relative humidity of particles,the more the hygroscopic growth factor f changes with relative humidity.Through increasing the solute soluble inorganic aerosol influences critical saturated ratio so as to make the hygroscopic growth factor f increase.If the role of unsolvable nucleation doesn't be taken into account,the hygroscopic growth of particles will be overestimated.With the velocity rising,the hygroscopic growth factor reduces,and the reduction degree depends on initial relative humidity.The lifting height can influence the hygroscopic growth factor through the change of relative humidity.
Jung C. H., Y. P. Kim, and K. W. Lee, 2003: A moment model for simulating raindrop scavenging of aerosols. J. Aerosol Sci., 34, 1217- 1233.10.1016/S0021-8502(03) The dynamics of a polydispersed aerosol size distribution, scavenged by precipitation, are numerically studied. The collision efficiency formula proposed by Slinn (Precipitation Scavenging in Atmospheric Sciences and Power Production—1979, Division of Biomedical Environmental Research, US Department of Energy, Washington, DC, USA, 1983, Chapter 11) and the moment method were introduced to represent the particle removal mechanism by raindrops and the aerosol size distribution, respectively. Consequently, the dynamics of the particle size distribution were reduced to a set of ordinary differential equations using the moment approach. A generalized raindrop distribution, including two widely used distributions; the Marshall–Palmer (MP) and Krigian–Mazin (KM) raindrop distributions, was adopted.Our model results have shown that raindrops with smaller diameters, and narrower distributions, collect aerosols more efficiently. Further, it was shown, in the small particle size region that the geometric mean diameter increases, while in the large particle region it decreases. For the two size ranges, the geometric standard deviations decrease with time, and a scavenging gap, the minimum particle removal efficiency region, exists between these particle size ranges.The dynamics of the particle size distributions, the MP and KM raindrop distributions, in the small particle range, show that the effects of the overestimation in the MP distribution were not as great as expected. Also, this study ascertained that the conventional parameterization of the constant collision efficiency introduces significant errors for estimating the particle size distribution dynamics by wet scavenging.
Jung C. H., S. Y. Bae, and Y. P. Kim, 2011: Approximated solution on the properties of the scavenging gap during precipitation using harmonic mean method. Atmos. Res., 99, 496- 504.10.1016/ deposition refers to both natural and artificial processes where particles are scavenged by atmospheric hydrometeors. Below-cloud atmospheric particles are removed by raindrops via Brownian diffusion, interception, and impaction. The overall scavenging coefficient has a broad and distinctive minimum for aerosol penetration between 0.1 and several micrometers in diameter. In this study, the approximated analytical solution for most penetrating particle size during precipitation was obtained. Brownian diffusion and interception were considered under the assumption of the inertial impaction can be neglected in this study conditions. Both the minimum collection efficiency and minimum scavenging coefficient particle size were estimated using the harmonic mean type approximation, with the solution compared to the numerically calculated results. The approximated results were comparable with the numerical solutions. The results showed that collection efficiency diameter is a function of terminal velocity and the collection mechanisms included. When considering Brownian diffusion and interception, most penetrating particle size increases as drop diameter increases, which shows a contrary to the study of Wang (1978) and this shows that most penetrating particle size depends on collection efficiency mechanism, flow velocity and collector diameter. Consequently, this study analytically approximated general type-solutions for scavenging gap particle size and minimum collection efficiency during precipitation.
Kaufman Y. J., D. Tanrè, and O. Boucher, 2002: A satellite view of aerosols in the climate system. Nature, 419, 215- 223.10.1038/ aerosols are intricately linked to the climate system and to the hydrologic cycle. The net effect of aerosols is to cool the climate system by reflecting sunlight. Depending on their composition, aerosols can also absorb sunlight in the atmosphere, further cooling the surface but warming the atmosphere in the process. These effects of aerosols on the temperature profile, along with the role of aerosols as cloud condensation nuclei, impact the hydrologic cycle, through changes in cloud cover, cloud properties and precipitation. Unravelling these feedbacks is particularly difficult because aerosols take a multitude of shapes and forms, ranging from desert dust to urban pollution, and because aerosol concentrations vary strongly over time and space. To accurately study aerosol distribution and composition therefore requires continuous observations from satellites, networks of ground-based instruments and dedicated field experiments. Increases in aerosol concentration and changes in their composition, driven by industrialization and an expanding population, may adversely affect the Earth's climate and water supply.
Khain A. P., M. B. Pinsky, 1997: Turbulence effects on the collision kernel. II: Increase of the swept volume of colliding drops. Quart. J. Roy. Meteor. Soc., 123, 1543- 1560.10.1002/ Available
Khoshsima M., F. Ahmadi-Givi, A. A. Bidokhti, and S. Sabetghadam, 2014: Impact of meteorological parameters on relation between aerosol optical indices and air pollution in a sub-urban area. J. Aerosol Sci., 68, 46- 57.10.1016/ Aerosol optical depth (AOD) provides a useful characterization of the total absorption and scattering effect of particles in direct or scattered sunlight, and can be derived from sun spectra measured directly by sun photometers. In this paper, atmospheric optical properties (e.g. AOD440–1020 nm, α and β, the coefficients in Angstrom formula) and meteorological conditions are presented for: summer (July-August-September) and winter (December-January-February-March) of 2009–2010 over Zanjan (36.41° N, 48.29° E) in northwestern Iran. The diurnal variation of AOD in Zanjan is approximately 15%. An exponential dependence of α on AOD in winter indicates that dust aerosols are major contributions of atmospheric turbidity in this region. AOD regressed against PM10 to establish prediction models. The role of three meteorological parameters on the correlation of AOD and PM10 are analyzed. Results show that there is a high correlation between AOD440 and PM10 in wintertime, and β is a better indicator of air quality in winter than in summer for the study region considered here. Hourly analysis shows that this correlation is highest in the afternoon when the atmospheric mixed layer is at its highest thickness. A similar behavior for AOD-PM10 and a correlation between optical properties with NO2 and PM10 are detected. A sensitivity study was designed to quantify the role of meteorological properties, such as relative humidity, wind speed, and temperature, on the correlation between AOD and PM10 concentration.
Kulshrestha U. C., L. A. K. Reddy, J. Satyanarayana, and M. J. Kulshrestha, 2009: Real-time wet scavenging of major chemical constituents of aerosols and role of rain intensity in Indian region. Atmos. Environ., 43( 32), 5123- 5127.10.1080/ simultaneous studies on chemical characteristics of rainwater and PM_(10) aerosols were carried out to understand the scavenging of major chemical components in Indian region. The concentrations of Ca~(2+), NH_4~+, SO_4~(2-) and NO_3~- were observed to be lower in the aerosol samples collected during rain as compared to before and after rain events. The most significant reduction was noticed for Ca~(2+) (74%) during rain which showed highest scavenging ratio (SR) and indicated that below-cloud scavenging is an effective removal process for Ca~(2+) in Indian region. Among non-sea salt components, Ca~(2+) had highest SR at Hyderabad indicating typical characteristics of crustal influence as abundance of calcium carbonate in soil dust has been reported in India. However, the levels of these major chemical components gradually got build-up in due course of time. After rain events, the levels of SO_4~(2+) aerosols were noticed to be substantially higher (more than double) within 24 h. In general, scavenging ratios for all components (except Ca~(2+), NH_4~+ and K~+) were higher over BOB as compared to Hyderabad. The maximum fall in aerosol levels (BR minus AR) was observed during continuous and low intensity rain events that did not allow building up of aerosol concentrations.
Li, Z. K, Y. X. Pan, R. Q. Sun, 1985: The Principle and Application of Air Pollution Meteorology. China Meteorological Press, 598 pp. (in Chinese)
Loosmore G. A., R. T. Cederwall, 2004: Precipitation scavenging of atmospheric aerosols for emergency response applications: Testing an updated model with new real-time data. Atmos. Environ., 38, 993- 1003.10.1016/ scavenging can effectively remove particulates from the atmosphere. Interest in the phenomena waxed in the 1980s, but models developed at that time remain limited by the lack of both detailed, time-resolved wet deposition pattern measurements for model confirmation and real-time rain data for model execution. Recently, new rain products have become available that can revolutionize real-time use of precipitation scavenging models on the regional scale. We have utilized a 4-km, hourly resolution precipitation data set from the Arkansas Red-Basin River Forecast Center. A standard below-cloud aerosol scavenging model has been modified to incorporate the potentially larger scavenging in heavy rain events. This paper demonstrates the model on a sample rainfall data set. The simulations demonstrate the concentrating effect of rainfall, especially heavy rain, on deposition patterns. Wet deposition played an important role in the simulated fate and transport, removing as much as 70% of the released aerosol.
Menon S., J. Hansen, L. Nazarenko, and Y. F. Luo, 2002: Climate effects of black carbon aerosols in China and India. Science, 297, 2250- 2253.10.1126/ recent decades, there has been a tendency toward increased summer floods in south China, increased drought in north China, and moderate cooling in China and India while most of the world has been warming. We used a global climate model to investigate possible aerosol contributions to these trends. We found precipitation and temperature changes in the model that were comparable to those observed if the aerosols included a large proportion of absorbing black carbon ("soot"), similar to observed amounts. Absorbing aerosols heat the air, alter regional atmospheric stability and vertical motions, and affect the large-scale circulation and hydrologic cycle with significant regional climate effects.
Mircea M., S. Stefan, and S. Fuzzi, 2000: Precipitation scavenging coefficient: Influence of measured aerosol and raindrop size distributions. Atmos. Environ., 34, 5169- 5174.10.1016/S1352-2310(00) scavenging coefficients, widely used in pollution studies, are derived from microphysical parameterisations of aerosol particles and raindrop populations and parameterisations of their interactions. The present study investigates the effects of measured aerosol and raindrop size distributions in a microphysical polydisperse framework. The interactions between aerosol and raindrops parameterised as collision efficiency are explicitly included to account for Brownian diffusion, inertial impaction and interception. Estimated values of the polydisperse scavenging coefficients exhibit variations of orders of magnitude depending on the aerosol type and almost no variation with the raindrop size distributions. For practical use, linear relationships between the scavenging coefficients and rain intensity for different aerosol types are derived.
Pan, L., Coauthors, 2010: Aerosol optical properties based on ground measurements over the Chinese Yangtze Delta Region. Atmos. Environ., 44, 2587- 2596.10.1016/ analysis results between aerosol optical properties and wind measurement at Pudong showed that the wind speed from the east correlates with the lower observed AOD. The back trajectory analysis indicates that more than 50% airmasses were from the marine area at Pudong, while back trajectories distribution is relatively homogeneous at Lin’an.
Pinsky M., M. Shapiro, A. P. Khain, and A. Pokrovsky, 2000: Investigation of the process of in- and below cloud aerosol scavenging from the atmosphere. J. Aerosol Sci., 31, 295- 296.10.1016/S0021-8502(00)
Qiu J. H., D. R. Lv, H. B. Chen, G. C. Wang, and G. Y. Shi, 2003: Modern research progresses in atmospheric physics. Chinese J. Atmos. Sci., 27, 628- 652. (in Chinese) paper briefly surnmarizes modern research content of the atmospheric physics and its development history, and it emphatically treats out research progresses and results (especially innovate results) in five fields of the atmospheric physics, contributed by scientists in the Institute of Atmospheric Physics, Chinese Academy of Sciences. These research fields include interaction between cloud and radiation, aerosol optical properties and its radiative forcing, atmospheric radiative transfer, and atmospheric composition measurements.
Ramanathan V., P. J. Crutzen, J. T. Kiehl, and D. Rosenfeld, 2001: Aerosols, climate, and the hydrological cycle. Science, 294, 2119- 2124.10.1126/ activities are releasing tiny particles (aerosols) into the atmosphere. These human-made aerosols enhance scattering and absorption of solar radiation. They also produce brighter clouds that are less efficient at releasing precipitation. These in turn lead to large reductions in the amount of solar irradiance reaching Earth's surface, a corresponding increase in solar heating of the atmosphere, changes in the atmospheric temperature structure, suppression of rainfall, and less efficient removal of pollutants. These aerosol effects can lead to a weaker hydrological cycle, which connects directly to availability and quality of fresh water, a major environmental issue of the 21st century.
Rasch, P. J., Coauthors, 2000: A comparison of scavenging and deposition processes in global models: results from the WCRP Cambridge Workshop of 1995. Tellus B, 52, 1025- 1056.10.1034/ report on results from a World Climate Research Program workshop on representations of scavenging and deposition processes in global transport models of the atmosphere. 15 models were evaluated by comparing simulations of radon, lead, sulfur dioxide, and sulfate against each other, and against observations of these constituents. This paper provides a survey on the simulation differences between models. It identifies circumstances where models are consistent with observations or with each other, and where they differ from observations or with each other. The comparison shows that most models are able to simulate seasonal species concentrations near the surface over continental sites to within a factor of 2 over many regions of the globe. Models tend to agree more closely over source (continental) regions than for remote (polar and oceanic) regions. Model simulations differ most strongly in the upper troposphere for species undergoing wet scavenging processes. There are not a sufficient number of observations to characterize the climatology (long-恡erm average) of species undergoing wet scavenging in the upper troposphere. This highlights the need for either a different strategy for model evaluation (e.g., comparisons on an event by event basis) or many more observations of a few carefully chosen constituents.
Santachiara G., F. Prodi, and F. Belosi, 2013: Atmospheric aerosol scavenging processes and the role of thermo- and diffusio-phoretic forces. Atmos. Res., 128, 46- 56.10.1016/ decrease in scavenging efficiency as a function of crystal diameter is reported both theoretically and experimentally. By comparing aerosol scavenging by drops and snow, most studies agree that, in terms of equal mass of precipitation, snow is more efficient at scavenging atmospheric particles than rain.
Schumann T., 1991: Aerosol and hydrometeor concentrations and their chemical composition during winter precipitation along a mountain slope II. Size-differentiated in-cloud scavenging efficiencies. Atmospheric Environment. Part A: General Topics, 1991, 25, 809- 824.
Sparmacher H., K. Fülber, and H. Bonka, 1993: Below-cloud scavenging of aerosol particles: Particle-bound radionuclides閳ユ柡锟芥摗xperimental. Atmos. Environ., 27, 605- 618.
Textor, C., Coauthors, 2006: Analysis and quantification of the diversities of aerosol life cycles within AeroCom. Atmos. Chem. Phys.,6, 1777-1813, doi: 10.5194/acp-6-1777-2006.10.5194/ results of global aerosol models have been assembled in the framework of the AeroCom intercomparison exercise. In this paper, we analyze the life cycles of dust, sea salt, sulfate, black carbon and particulate organic matter as simulated by sixteen global aerosol models. The differences among the results (model diversities) for sources and sinks, burdens, particle sizes, water uptakes, and spatial dispersals have been established. These diversities have large consequences for the calculated radiative forcing and the aerosol concentrations at the surface. Processes and parameters are identified which deserve further research. The AeroCom all-models-average emissions are dominated by the mass of sea salt (SS), followed by dust (DU), sulfate (SO4), particulate organic matter (POM), and finally black carbon (BC). Interactive parameterizations of the emissions and contrasting particles sizes of SS and DU lead generally to higher diversities of these species, and for total aerosol. The lower diversity of the emissions of the fine aerosols, BC, POM, and SO4, is due to the use of similar emission inventories, and does therefore not necessarily indicate a better understanding of their sources. The diversity of SO4-sources is mainly caused by the disagreement on depositional loss of precursor gases and on chemical production. The diversities of the emissions are passed on to the burdens, but the latter are also strongly affected by the model-specific treatments of transport and aerosol processes. The burdens of dry masses decrease from largest to smallest: DU, SS, SO4, POM, and BC. The all-models-average residence time is shortest for SS with about half a day, followed by SO4 and DU with four days, and POM and BC with six and seven days, respectively. The wet deposition rate is controlled by the solubility and increases from DU, BC, POM to SO4 and SS. It is the dominant sink for SO4, BC, and POM, and contributes about one third to the total removal of SS and DU species. For SS and DU we find high diversities for the removal rate coefficients and deposition pathways. Models do neither agree on the split between wet and dry deposition, nor on that between sedimentation and other dry deposition processes. We diagnose an extremely high diversity for the uptake of ambient water vapor that influences the particle size and thus the sink rate coefficients. Furthermore, we find little agreement among the model results for the partitioning of wet removal into scavenging by convective and stratiform rain. Large differences exist for aerosol dispersal both in the vertical and in the horizontal direction. In some models, a minimum of total aerosol concentration is simulated at the surface. Aerosol dispersal is most pronounced for SO4 and BC and lowest for SS. Diversities are higher for meridional than for vertical dispersal, they are similar for the individual species and highest for SS and DU. For these two components we do not find a correlation between ve
Wang X., L. Zhang, and M. D. Moran, 2010: Uncertainty assessment of current size-resolved parameterizations for below-cloud particle scavenging by rain. Atmos. Chem. Phys.,10, 5685-5705, doi: 10.5194/acp-10-5685-2010.10.5194/ theoretical and empirical size-resolved parameterizations of the scavenging coefficient (Λ), a parameter commonly used in aerosol transport models to describe below-cloud particle scavenging by rain, have been reviewed in detail and compared with available field and laboratory measurements. Use of different formulations for raindrop-particle collection efficiency can cause uncertainties in size-resolved Λ values of one to two orders of magnitude for particles in the 0.01–3 μm diameter range. Use of different formulations of raindrop number size distribution can cause Λ values to vary by a factor of 3 to 5 for all particle sizes. The uncertainty in Λ caused by the use of different droplet terminal velocity formulations is generally small than a factor of 2. The combined uncertainty due to the use of different formulations of raindrop-particle collection efficiency, raindrop size spectrum, and raindrop terminal velocity in the current theoretical framework is not sufficient to explain the one to two order of magnitude under-prediction of Λ for the theoretical calculations relative to the majority of field measurements. These large discrepancies are likely caused by additional known physical processes (i.e, turbulent transport and mixing, cloud and aerosol microphysics) that influence field data but that are not considered in current theoretical Λ parameterizations. The predicted size-resolved particle concentrations using different theoretical Λ parameterization can differ by up to a factor of 2 for particles smaller than 0.01 μm and by a factor of >10 for particles larger than 3 μm after 2–5 mm of rain. The predicted bulk mass and number concentrations (integrated over the particle size distribution) can differ by a factor of 2 between theoretical and empirical Λ parameterizations after 2–5 mm of moderate intensity rainfall.
Xia X. G., H. B. Chen, Z. Q. Li, P. C. Wang, and J. K. Wang, 2007a: Significant reduction of surface solar irradiance induced by aerosols in a suburban region in northeastern China. J. Geophys. Res., 112,D22S02, doi: 10.1029/2006JD007562.10.1029/ the spring of 2005, a Sun photometer and a set of broadband pyranometers were installed in Liaozhong, a suburban region in northeastern China. Aerosol properties derived from Sun photometer measurements and aerosol-induced changes in downwelling shortwave surface irradiances are analyzed in this paper. It is shown that the mean aerosol optical depth (AOD) at 500 nm is 0.63. The day-to-day variation of aerosol optical depth is dramatic, with a maximum daily AOD close to 2.0 and a minimum value close to the background level. Dust activities generally produce heavy aerosol loading characterized by larger particle sizes and less absorption than those observed under normal conditions. The reduction of instantaneous direct shortwave surface irradiance per unit of AOD is 404.5 W m. About 63.8% of this reduction is offset by an increase in diffuse irradiance; consequently, one unit increase in AOD leads to a decrease in global surface irradiance of 146.3 W m. The diurnal aerosol direct radiative forcing efficiency is about -47.4 W m. Overall, aerosols reduce about 30 W mper day of surface net shortwave irradiance in this suburban region.
Xia X. G., Z. Q. Li, B. Holben, P. C. Wang, T. Eck, H. B. Chen, M. Cribb, and Y. X. Zhao, 2007b: Aerosol optical properties and radiative effects in the Yangtze Delta region of China. J. Geophys. Res., 112,D22S12, doi: 10.1029/2007JD008859.10.1029/ year's worth of aerosol and surface irradiance data from September 2005 to August 2006 were obtained at Taihu, the second supersite for the East Asian Study of Tropospheric Aerosols: An International Regional Experiment (EAST-AIRE). Aerosol optical properties derived from measurements by a Sun photometer were analyzed. The aerosol data were used together with surface irradiance data to quantitatively estimate aerosol effects on surface shortwave radiation (SWR) and photosynthetically active radiation (PAR). The annual mean aerosol optical depth at 500 nm is 0.77, and mean ngstrom wavelength exponent is 1.17. The annual mean aerosol single scattering albedo and mean aerosol asymmetry factor at 440 nm are 0.90 and 0.72, respectively. Both parameters show a weak seasonal variation, with small values occurring during the winter and larger values during the summer. Clear positive relationships between relative humidity and aerosol properties suggest aerosol hygroscopic growth greatly modifies aerosol properties. The annual mean aerosol direct radiative forcing at the surface (ADRF) is -38.4 W mand -17.8 W mfor SWR and PAR, respectively. Because of moderate absorption, the instantaneous ADRF at the top of the atmosphere derived from CERES SSF data is close to zero. Heavy aerosol loading in this region leads to -112.6 W mand -45.5 W mreduction in direct and global SWR, but 67.1 W mmore diffuse SWR reaching the surface. With regard to PAR, the annual mean differences in global, direct and diffuse irradiance are -23.1 W m, -65.2 W mand 42.1 W mwith and without the presence of aerosol, respectively.
Yang J., B. Zhu, and Z. H. Li, 2001: Physicochemical properties of atmospheric aerosol particles at Zetang and Jinghong of China. Acta Meteorologica Sinica, 59, 795- 802. (in Chinese) aerosol particles were measured at Jinghong (Yunnan Province)and Zetang (Ti bet Region )meteorological observatories in the winter 1997/1998, and their physicochemical properties, such as mass concentration, size distribution, optical absorption coefficient and chemical composition, were analyzed. Results show that aerosol particles at the two sites have significant physical and chemical difference and also different from the results at other locations. Zetang has a low number density with a relative high mass concentration. This study has great practical importance to add to our knowledge of Chinese aerosol distribution and their effects on the regional climate.
Yin Y., C. Chen, K. Chen, J. L. An, W. W. Wang, Z. Y. Lin, J. D. Yan, and J. Wang, 2010: An observational study of the microphysical properties of atmospheric aerosol at Mt. Huang. Transactions of Atmospheric Sciences, 33, 129- 136. (in Chinese)10.1016/ on observational data of atmospheric aerosol from April to July 2008 at the top of Mt.Huang,the characteristics of aerosol particles such as number concentration,size distribution and its relationship with meteorological factors were analyzed and a comparison was made between cloudy/foggy and clear weather conditions.The results show that the mean number concentration reaches 3.14×103 cm-3 in spring,and 1.80×103 cm-3 in summer,respectively,and ultra fine particles(smaller than 0.1 μm in diameter) account for 79% and 68%,respectively,in the total number concentration in spring and summer.It is also shown that the size distribution of aerosol particles all appear as a single mode spectrum in spring and summer,with the peak value concentrating at particle sizes of 0.04—0.12 μm and that the accumulation mode particles(0.1—1.0 μm in diameter) dominate in the volume and surface distributions.It is found that the concentration of fine particles is higher under non-foggy weather conditions as compared with foggy periods and that particle concentration is positively correlated with the air temperature and negatively correlated with relative humidity.The results also show that while northwest and southerly winds dominate in spring,the particle concentration is highest when it is northwest.In summer,high particle concentration is observed when the wind blows from the east.
Yoo, J.-M., Coauthors, 2014: New indices for wet scavenging of air pollutants (O3, CO, NO2, SO2, and PM10 by summertime rain. Atmos. Environ., 82, 226- study has analyzed the concentration variation of four air pollutants (PM, NO60, CO, and SO60) during the typhoon periods over 10 years (2002~2011). In this study, 10 typhoon events which had rainfalls in Korean Peninsula were selected during the study period. The analysis was performed using the observation data of both the air pollutants and rainfall. In order to examine and compare the concentrations of the air pollutants between normal periods and typhoon periods, we have obtained monthly average concentrations from July to September and daily average concentrations during typhoon periods. For the period from July to September, 34% of the total rainfalls can be explained by typhoons, and the concentration of air pollutants during the typhoon period was lower than the normal period. In addition, the concentration variations of the pollutants during the typhoon period were analyzed according to two categories: differences in the concentrations between the day before and the day of the typhoon (Case 1) and between the day before and after the typhoon (Case 2). The results indicated that the reduction rate of PM, NO60, CO, and SO60 was 30.1%, 17.9%, 11.6%, 9.7% (Case 1) and 22.8%, 21.0%, 9.0%, 8.0% (Case 2), respectively. This result suggested that air quality was significantly improved during the typhoon period than after the typhoon period by the rainfall.
Zhang L. M., D. V. Michelangeli, and P. A. Taylor, 2004: Numerical studies of aerosol scavenging by low-level, warm stratiform clouds and precipitation. Atmos. Environ., 38, 4653- 4665.10.1016/ studies have been performed to investigate aerosol scavenging by low-level, warm stratiform clouds and precipitation using a one-dimensional model with detailed cloud microphysics and size resolved aerosol particles and hydrometeors. Activation processes remove most aerosol mass within the cloud layer despite the very low supersaturation, since a large fraction of the aerosol mass is associated with large aerosols which can be quickly activated into cloud droplets. Impaction scavenging inside the cloud layer removes little aerosol mass; however, this process removes aerosols as high as 50% in number during a period of a few hours. Total in-cloud scavenging removes more than 70% of aerosols in number and more than 99% in mass. Below cloud scavenging is linked to aerosol concentration and size distribution, precipitation intensity and droplet spectra. During a 4-h period, weak precipitation having less than 0.1 mm h intensity can remove 50-80% of the below-cloud aerosol in both number and mass. Scavenging coefficients for large particles vary significantly with precipitation rates and/or droplet mean radii while for small particles such variation is not apparent. As a result, bulk aerosol mass-scavenging coefficients depend strongly on precipitation intensity while bulk number scavenging coefficients have less dependence. A dependence of scavenging coefficients for all size particles on total droplet surface area is found to be possible and such dependence is stronger for smaller particles. With the same precipitation amount, precipitation with more small droplets can remove aerosols more effectively due to larger total droplet surface area. Size-resolved scavenging coefficients have to be used in order to correctly track both aerosol number and mass distributions. It is suggested that parameterizations for bulk or size-resolved scavenging coefficients should be a function of other precipitation properties as well as precipitation intensity.
Zhang X. L., Y. Huang, and R. Rao, 2012: Aerosol characteristics including fumigation effect under weak precipitation over the southeastern coast of China. Journal of Atmospheric and Solar-Terrestrial Physics,84-85, 25- 36.10.1016/ size distribution, total number concentration, scattering coefficient and absorption coefficient were measured in Quanzhou on the southeastern coast of China, from December 13, 2010 to January 16, 2011. Five light-rain events were analyzed for statistical study and one typical light-rain process was chosen as the case study for analysis in detail. The study focuses on the influence of weak precipitation on aerosol light-scattering and absorption properties as well as the size distribution. Similar size distributions were observed between clear-day regime and light-rain regime. The scavenging coefficient in the scavenging gap was about 10swith the mean precipitation intensity of 0.5 mm/h, which were significantly larger than those of model estimations but close to those from other field measurements. Fumigation effect was also observed in the light-rain day due to the downward flow from the clouds at the beginning of precipitation in this measurement.
Zhao H. B., C. G. Zheng, 2006: Monte Carlo solution of wet removal of aerosols by precipitation. Atmos. Environ., 40, 1510- 1525.10.1016/ time evolution of aerosol size distribution (ASD) during precipitation describes quantitatively aerosols wet scavenging process. Scavenging coefficient, which takes account of the three most important wet removal mechanisms: Brownian diffusion, interception and inertial impaction, is used to parameterize wet scavenging process. A new multi-Monte Carlo method (MMC) is promoted to solve general dynamic equation for wet removal of aerosols. Two special cases in which analytical solutions exist are adopted to validate computation precision of MMC method. Furthermore, the influence of precipitation type on aerosols wet scavenging process is investigated by numerical simulation of the method. The results show that for lognormal raindrop size distribution and lognormal ASD (1) the increase of rainfall intensity (from light precipitation to moderate precipitation and then to heavy precipitation) can help scavenge aerosols with any size; (2) any precipitation type scavenges large aerosols (>2 渭m) more effectively than small aerosols (0.01 渭m and <2 渭m) (in that order); (3) the three precipitation types have a weak effect of wet scavenging on intermediate aerosols.
Zheng B., D. Wu, F. Li, and T. Deng, 2013: Variation of aerosol optical characteristics in Guangzhou on a backgroud of South China Sea summer monsoon. Journal of Tropical Meteorology, 29, 207- 214. (in Chinese) order to study the variation of Guangzhou’s aerosol optical characteristics on a large-scale background of South China Sea summer monsoon(SCSSM) and its possible cause,aerosol data derived at Panyu Atmospheric Composition Watch Station in Guangzhou and National Centers for Environmental Prediction/National Center for Atmospheric Research(USA) reanalysis data are used to take composite analysis and do physical diagnoses.Main results showed that aerosol extinction in Guangzhou increases first and then decreases during the active period of SCSSM.The data analyses indicate that stratification variation of the planetary boundary layer and environmental winds play important roles in affecting Guangzhou’s aerosol optical characteristics.To a great extent,stratification of the planetary boundary layer is modified by regional diabatic heating and anomalous cyclonic circulation excited by monsoon convection would induce the environmental winds anomalies.