Journal
ATMOSPHERIC CHEMISTRY AND PHYSICS
Volume 20, Issue 11, Pages 6435-6453Publisher
COPERNICUS GESELLSCHAFT MBH
DOI: 10.5194/acp-20-6435-2020
Keywords
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Funding
- National Key Research and Development Program of China [2017YFC0210104, 2016YFC0203305]
- National Natural Science Foundation of China [41505106, 41875152, 21577177]
- National Science Fund for Distinguished Young Scholars [41425020]
- Fundamental Research Funds for the Central Universities [16lgpy28]
- National Natural Science Foundation [91644215, 41630422]
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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 mu m. In autumn, the nitrate size distribution was bimodal, peaking at 0.44-1.0 and 2.5-10 mu m, 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.
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