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Discussion papers | Copyright
© Author(s) 2018. This work is distributed under
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Research article 12 Apr 2018

Research article | 12 Apr 2018

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This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Chemistry and Physics (ACP).

Intra-annual variations of regional aerosol optical depth, vertical distribution, and particle types from multiple satellite and ground-based observational datasets

Bin Zhao1, Jonathan H. Jiang2, David J. Diner2, Hui Su2, Yu Gu1, Kuo-Nan Liou1, Zhe Jiang1, Lei Huang1, Yoshi Takano1, Xuehua Fan1, and Ali H. Omar3 Bin Zhao et al.
  • 1Joint Institute for Regional Earth System Science and Engineering and Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California, USA
  • 2Jet propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
  • 3NASA Langley Research Center, Hampton, Virginia , USA

Abstract. The relatively short lifetimes of aerosols in the atmosphere result in climatic and health effects that are strongly dependent on intra-annual variations in particle concentrations. While many studies have examined the seasonal and diurnal variations of regional aerosol optical depth (AOD), understanding the temporal variations in aerosol vertical distribution and particle types is also important for accurate computation of aerosol radiative effects. In this paper, we combine the observations from four satellite-borne sensors and ground-based AOD and fine particle (PM2.5) measurements to investigate the seasonal and diurnal variations of aerosol column loading, vertical distribution, and particle types over three populous regions: the Eastern United States (EUS), Western Europe (WEU), and Eastern and Central China (ECC). In all three regions, column AOD, as well as AOD higher than 800m above ground level, peaks in summer/spring probably due to accelerated formation of secondary aerosols and hygroscopic growth. However, AOD at height below 800m mostly peaks in winter except that a second maximum in summer occurs over the EUS region, which is consistent with observed temporal trends in surface PM2.5 concentrations. AOD due to fine particles (<0.7μm diameter) is much larger in spring/summer than in winter over all three regions, whereas coarse mode AOD (>1.4μm diameter) generally shows less variability, except for the ECC region where a peak occurs in spring, consistent with the prevalence of airborne dust during this season. When aerosols are classified according to sources, the dominant type is associated with anthropogenic air pollution, which has a similar seasonal pattern as total AOD. Dust and sea-spray aerosols in the WEU region peak in summer and winter, respectively, but do not show an obvious seasonal pattern in the EUS region. Smoke aerosols, as well as absorbing aerosols, present an obvious unimodal distribution with a maximum occurring in summer over the EUS and WEU regions, whereas they follow a bimodal distribution with peaks in August and March (due to crop residue burning) over the ECC region. In general, the nighttime-daytime AOD difference is more positive in summer than in winter, likely attributable to a larger diurnal temperature range in summer. Smoke AOD is much higher in the nighttime than in the daytime. The results of this study can help to improve the current estimates of the climatic and health impacts of aerosols.

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Bin Zhao et al.
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Short summary
We combine satellite-borne and ground-based observations to investigate the intraannual variations of regional aerosol column loading, vertical distribution, and particle types. Column aerosol optical depth (AOD), as well as AOD > 800 m, peaks in summer/spring. However, AOD < 800 m and surface PM2.5 concentrations mostly peak in winter. The aerosol intraannual variations also differ significantly according to aerosol types characterized by different sizes, light absorption, and emission sources.
We combine satellite-borne and ground-based observations to investigate the intraannual...