Vertical Structural Characteristics of Aerosols in the Atmospheric Boundary Layer during the Summer in Lhasa
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摘要: 大气污染物的垂直梯度观测是识别区域输送和本地贡献的必要手段。基于此,2020年8月在拉萨市利用光学粒子计数器(the Printed Optical Particle Spectrometer,简称POPS)在地面和系留气艇分别对0.13~3.39 μm粒径范围的气溶胶数浓度进行了测定。结果表明:(1)拉萨近地面气溶胶数浓度在16 cm−3到870 cm−3范围之间,比华北和珠江三角洲地区小2~3个量级;(2)气溶胶数浓度呈现两峰两谷的日变化结构,峰值通常以0.13~0.4 μm的小粒径粒子为主,且对应北京时间早(10:00)、晚(21:00)高峰时段;(3)气溶胶数浓度垂直分布与边界层演变密切相关,稳定边界层中的气溶胶随高度递减,粒子数浓度为194±94 cm−3,对流边界层和残留层中的气溶胶分布均一,数浓度分别为165±99 cm−3和123±95 cm−3,且显著低于稳定边界层。以上研究结果表明,拉萨的污染源主要为局地机动车排放,机动车污染物减排是打造高原生态旅游城市的必由之路。Abstract: To determine regional transport and local contribution, vertical gradient observation of air pollutants is required. Based on this, the number concentrations of aerosols in the particle size range of 0.13–3.39 μm were recorded with an optical particle counter POPS (the Printed Optical Particle Spectrometer) at ground level and in a tethered airboat in Lhasa in August 2020. The results demonstrate that (1) near-ground aerosol number concentrations in Lhasa range from 16 cm−3 to 870 cm−3, which is 2–3 orders of magnitude lower than those in northern China and the Yangtze River Delta. (2) The daily variation structure of the aerosol number concentration display two peaks and valleys. The peaks, which correlate to morning and evening peaks [1000 BJT (Beijing time) and 2100 LT, respectively], are usually dominated by small particles of 0.13–0.4 μm. (3) Furthermore, the vertical distribution of the aerosol number concentration is closely related to the evolution of the boundary layer. The aerosol in the stable boundary layer decreases with height, and the particle number concentration is 194± 94 cm−3. Conversely, the aerosols in the convective boundary and residual layers are uniformly distributed with the number concentrations of 165±99 cm−3 and 123±95 cm−3, respectively, which are significantly lower than that in the stable boundary layer. According to the above research results, local motor vehicle emissions are the main sources of pollution in Lhasa. Therefore, motor vehicles must be controlled and emissions must be reduced to build a highland ecotourism city.
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Key words:
- Boundary layer structure /
- Aerosol /
- Vertical profile /
- Lhasa /
- Number concentration
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图 2 2020年8月整个观测期PM2.5和PM10(a)24小时均值浓度、(b)小时均值浓度、(c)NO2和SO2浓度、(d)气溶胶数浓度(CN)以及(e)气溶胶不同粒径数浓度随时间的变化(灰色竖线代表系留气艇释放时段)。(a)中红、蓝、黑虚线分别对应代表GB 3095-2012的24小时一级标准[C(PM2.5):35 μg m−3和C(PM10):55 μg m−3],以及WHO最新2021年的24小时标准[C(PM2.5):15 μg m−3]
Figure 2. Time series of (a) 24-h mean and (b) hourly mean of PM [C(PM10), C(PM2.5)], (c) NO2 concentration [C(NO2)] and SO2 concentration [C(SO2)], (d) particulate matter number concentrations (CN), and (e) particulate matter number concentrations (shaded) of different particle sizes (the gray vertical line represents the release period of the captive airship) in the whole observation period of August 2020. In (a), the red, blue, and black dotted lines correspond to the 24-h level 1 standard of GB 3095-2012 for PM2.5 (35 μg m−3) and PM10 (55 μg m−3) and the latest WHO 24-h standard of 2021 for PM2.5 (15 μg m−3), respectively
图 4 2020年8月(a)PM2.5、PM10浓度[C(PM2.5)、C(PM10)]和(b)NO2、SO2浓度[C(NO2)、C(SO2)]以及(c)气溶胶数浓度(CN)的日变化特征(误差线代表标准差);(d)不同粒径段气溶胶数浓度日变化特征
Figure 4. Diurnal variation of NO2, SO2, PM2.5, PM10, and particulate matter (the errorbar represents the standard deviation). (d) The particulate matter number concentrations in different particle size bins
图 5 2020年8月1日~28日存在的两种气溶胶数浓度垂直剖面类型(a)对流边界层(CBL);(b)稳定边界层(SBL):红线代表平均廓线;加粗黑线代表边界层位置;RL为残留层
Figure 5. Two types of particulate matter number concentrations (CN) vertical profiles that existed during 2020.08.01–2020.08.28 (a) convective boundary layer and (b) stable boundary layer. The red line represents the average profile, and the bold black line represents the boundary layer position; RL means residual layer
表 1 不同地区积聚模态粒子数浓度对比
Table 1. Comparison of the concentrations of accumulative modal particle numbers in different regions
观测地区 粒径/nm 数浓度/cm−3
平均值(±标准差)参考文献 济南(夏季) 100~1000 481±332 Gao et al.(2007) 太仓(夏季)) 100~1000 1745±1260 Gao et al.(2009) 北京(夏季) 100~2500 1859±837 Gao et al.(2012) 北京(夏季) 100~1000 7800±5400 Wu et al.(2008) 广州(夏季) 100~800 3210±2057 韩冰雪等(2015) 长江三角洲(夏季) 100~800 5300±5500 Qi et al.(2015) 邢台(夏季) 100~552/
100~6857019 Wang et al.(2021) 拉萨(夏季) 130~3900 154±100 本文 A1 边界层实验中所测量的混合状态下每个垂直剖面的日期、时间和其他信息(序号代表释放顺序)
A1. Date, time, and other information for each vertical section in the in the boundary layer experiment (the serial number represents the release sequence)
序号 日期 释放时间
(北京时)Ri 边界层高度/m 1 2020年8月8日 09:10 −1.59 200 2 2020年8月8日 10:27 −20.77 660 3 2020年8月8日 11:26 −443 700 4 2020年8月9日 11:49 −5.28 560 5 2020年8月9日 12:32 −6.86 700 6 2020年8月9日 13:20 −8.62 430 7 2020年8月9日 13:58 −12.91 450 8 2020年8月9日 14:40 −5.23 445 9 2020年8月9日 16:07 −7.04 900 10 2020年8月9日 16:50 −1.06 1000 11 2020年8月10日 12:28 −222.24 290 12 2020年8月10日 13:05 −13.86 500 13 2020年8月10日 13:42 −15.67 700 14 2020年8月11日 11:51 −24.31 390 15 2020年8月11日 12:39 −19.79 600 16 2020年8月11日 15:06 −63.11 1400 17 2020年8月11日 15:45 −41.37 1350 18 2020年8月12日 10:25 −4.72 480 19 2020年8月12日 12:13 −119.89 760 20 2020年8月12日 15:13 −77.63 800 21 2020年8月13日 10:13 −283.18 400 22 2020年8月14日 13:51 −15.16 490 23 2020年8月16日 10:44 −10.79 520 24 2020年8月16日 11:24 −5.38 700 25 2020年8月17日 11:14 −13.37 400 26 2020年8月17日 11:59 −10.85 620 27 2020年8月18日 7:10 0.77 310 28 2020年8月18日 12:53 −72.37 800 29 2020年8月19日 15:21 −61.37 2750 30 2020年8月19日 19:39 −9.83 590 31 2020年8月20日 13:06 −12.22 1100 32 2020年8月20日 21:20 0.96 500 33 2020年8月21日 12:45 −40.08 750 34 2020年8月21日 14:36 −12.9 1750 35 2020年8月22日 10:35 −14.39 700 36 2020年8月22日 13:58 −17.16 1300 37 2020年8月26日 12:35 −6 1440 38 2020年8月26日 19:11 −43.56 490 39 2020年8月27日 15:53 −7.64 2610 A2 边界层实验中所测量的稳定状态下每个垂直剖面的日期、时间和其他信息(序号代表释放顺序)
A2. Date, time, and other information for each vertical section in the boundary layer experiment(the serial number represents the release sequence)
序号 日期 释放时间
(北京时)Ri 边界层高度/m 1 2020年8月8日 07:52 1.85 220 2 2020年8月12日 07:05 14.59 620 3 2020年8月12日 08:36 11.61 700 4 2020年8月12日 09:28 2.34 280 5 2020年8月17日 07:09 26.56 200 6 2020年8月17日 08:05 19.98 340 7 2020年8月18日 21:52 1.53 340 8 2020年8月19日 21:10 7.31 420 9 2020年8月20日 07:12 8.42 200 10 2020年8月20日 08:49 3.52 550 11 2020年8月22日 07:12 25.59 200 12 2020年8月22日 21:28 2.87 500 13 2020年8月26日 07:11 15.36 580 14 2020年8月26日 22:01 15.87 350 15 2020年8月27日 07:09 2.1 190 16 2020年8月27日 21:19 8.64 340 17 2020年8月28日 06:53 13.58 660 18 2020年8月28日 08:20 3.44 300 -
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