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Volume 17, issue 21 | Copyright
Atmos. Chem. Phys., 17, 13473-13489, 2017
https://doi.org/10.5194/acp-17-13473-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 13 Nov 2017

Research article | 13 Nov 2017

Analysis of influential factors for the relationship between PM2.5 and AOD in Beijing

Caiwang Zheng1,2, Chuanfeng Zhao1,2,3, Yannian Zhu1,2,4, Yang Wang1,2, Xiaoqin Shi1,2, Xiaolin Wu1,2, Tianmeng Chen1,2, Fang Wu1,2, and Yanmei Qiu1,2 Caiwang Zheng et al.
  • 1State Key Laboratory of Earth Surface Processes and Resource Ecology, and College of Global Change and Earth System Science, Beijing Normal University, Beijing, 100875, China
  • 2Joint Center for Global Change Studies, Beijing, 100875, China
  • 3Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
  • 4Meteorological Institute of Shaanxi Province, Xi'an, China

Abstract. The relationship between aerosol optical depth (AOD) and PM2.5 is often investigated in order to obtain surface PM2.5 from satellite observation of AOD with a broad area coverage. However, various factors could affect the AOD–PM2.5 regressions. Using both ground and satellite observations in Beijing from 2011 to 2015, this study analyzes the influential factors including the aerosol type, relative humidity (RH), planetary boundary layer height (PBLH), wind speed and direction, and the vertical structure of aerosol distribution. The ratio of PM2.5 to AOD, which is defined as η, and the square of their correlation coefficient (R2) have been examined. It shows that η varies from 54.32 to 183.14, 87.32 to 104.79, 95.13 to 163.52, and 1.23 to 235.08µgm−3 with aerosol type in spring, summer, fall, and winter, respectively. η is smaller for scattering-dominant aerosols than for absorbing-dominant aerosols, and smaller for coarse-mode aerosols than for fine-mode aerosols. Both RH and PBLH affect the η value significantly. The higher the RH, the smaller the η, and the higher the PBLH, the smaller the η. For AOD and PM2.5 data with the correction of RH and PBLH compared to those without, R2 of monthly averaged PM2.5 and AOD at 14:00LT increases from 0.63 to 0.76, and R2 of multi-year averaged PM2.5 and AOD by time of day increases from 0.01 to 0.93, 0.24 to 0.84, 0.85 to 0.91, and 0.84 to 0.93 in four seasons respectively. Wind direction is a key factor for the transport and spatial–temporal distribution of aerosols originated from different sources with distinctive physicochemical characteristics. Similar to the variation in AOD and PM2.5, η also decreases with the increasing surface wind speed, indicating that the contribution of surface PM2.5 concentrations to AOD decreases with surface wind speed. The vertical structure of aerosol exhibits a remarkable change with seasons, with most particles concentrated within about 500m in summer and within 150m in winter. Compared to the AOD of the whole atmosphere, AOD below 500m has a better correlation with PM2.5, for which R2 is 0.77. This study suggests that all the above influential factors should be considered when we investigate the AOD–PM2.5 relationships.

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This study analyzes influential factors including the aerosol type, relative humidity (RH), atmospheric boundary layer height (BLH), wind speed and direction, and aerosol vertical structure to the AOD–PM2.5 relationship. It shows that the ratio of PM2.5 to AOD, η, varies a lot with aerosol type. η is smaller for scattering-dominant (coarse mode) than for absorbing-dominant (fine mode) aerosol. The higher the RH (BLH), the larger (smaller) the η. η also decreases with the surface wind speed.
This study analyzes influential factors including the aerosol type, relative humidity (RH),...
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