Measurement report: Vertical distribution of atmospheric particulate matter within the urban boundary layer in southern China – size-segregated chemical composition and secondary formation through cloud processing and heterogeneous reactions
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Published:2020-06-04
Issue:11
Volume:20
Page:6435-6453
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ISSN:1680-7324
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Container-title:Atmospheric Chemistry and Physics
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language:en
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Short-container-title:Atmos. Chem. Phys.
Author:
Zhou Shengzhen, Wu Luolin, Guo Junchen, Chen Weihua, Wang Xuemei, Zhao JunORCID, Cheng YafangORCID, Huang Zuzhao, Zhang Jinpu, Sun YeleORCID, Fu PingqingORCID, Jia Shiguo, Tao JunORCID, Chen Yanning, Kuang Junxia
Abstract
Abstract. Many studies have recently been done on understanding the sources
and formation mechanisms of atmospheric aerosols at ground level. However,
vertical profiles and sources of size-resolved particulate matter within the
urban boundary layer are still lacking. In this study, vertical distribution
characteristics of size-segregated particles were investigated at three
observation platforms (ground level, 118 m, and 488 m) on the 610 m high
Canton Tower in Guangzhou, China. Size-segregated aerosol samples were
simultaneously collected at the three levels in autumn and winter. Major
aerosol components, including water-soluble ions, organic carbon, and
elemental carbon, were measured. The results showed that daily average
fine-particle concentrations generally decreased with height.
Concentrations of sulfate and ammonium in fine particles displayed shallow
vertical gradients, and nitrate concentrations increased with height in
autumn, while the chemical components showed greater variations in winter
than in autumn. The size distributions of sulfate and ammonium in both
seasons were characterized by a dominant unimodal mode with peaks in the size
range of 0.44–1.0 µm. In autumn, the nitrate size distribution was
bimodal, peaking at 0.44–1.0 and 2.5–10 µm, while in winter
it was unimodal, implying that the formation mechanisms for nitrate
particles were different in the two seasons. Our results suggest that the
majority of the sulfate and nitrate is formed from aqueous-phase reactions,
and we attribute coarse-mode nitrate formation at the measurement site to
the heterogeneous reactions of gaseous nitric acid on existing sea-derived
coarse particles in autumn. Case studies further showed that atmospheric
aqueous-phase and heterogeneous reactions could be important mechanisms for
sulfate and nitrate formation, which, in combination with adverse weather
conditions such as temperature inversion and calm wind, led to haze
formation during autumn and winter in the Pearl River Delta (PRD) region.
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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