Impact of atmospheric circulations on aerosol distributions in autumn over eastern China: observational evidence

X Y Zheng,Y F Fu,Y J Yang,G S Liu

doi:10.5194/acp-15-12115-2015

X Y Zheng, Y F Fu + Show 2 more

Open Access

https://doi.org/10.5194/acp-15-12115-2015

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Abstract

Abstract. Regional heavy pollution events in eastern China (110–122° E, 28–40° N) are causing serious environmental problems. In this study, the relationship between the degree of regional pollution and the patterns of large-scale atmospheric circulation over eastern China in October is investigated using 10-year (2001–2010) Terra/MODIS aerosol optical depth and NCEP reanalysis data by both case study and composite analysis. Eighteen polluted and 10 clean episodes are selected and categorised into six polluted types and three clean types respectively. Generally speaking, weather patterns such as a uniform surface pressure field in eastern China or a steady straight westerly in the middle troposphere, particularly when being at the rear of the anticyclone at 850 hPa, are typically responsible for heavy pollution events. Meanwhile, clean episodes occur when strong southeastward cold air advection prevails below the middle troposphere or air masses are transported from sea to land. Uniform descending motion prevails over the study region, trapping pollutants in the lower atmosphere. Therefore, the value of vertical velocity averaged from 1000 to 100 hPa and divergence of wind field in the lower troposphere are used in this study to quantify the diffusion conditions in each circulation type. The results reveal that it is often a clean episode when both the mean downward motion (larger than 2.56 × 10−2 Pa s−1) and the divergence of low-level winds (larger than 1.79 × 10−2 s−1) are strong. Otherwise, it is more likely to be a polluted episode.

Highlights

IntroductionSince aerosols can modulate the radiation budget of the earth-atmosphere system, influence the climate and degrade air quality (Kaufman et al, 2002), they have long been attracting high attentions from scientific community (Twomey, 1977; Rosenfeld et al, 2004; Zhao et al, 2006a, b; Rosenfeld et al, 2007; Li et al, 2011; Koren et al, 2012; Zhao et al, 2012, 2013a, b; Chen et al, 2014)
We evaluate the above relationship during autumn using 10-year (2001–2010) Terra/MODIS (Moderate-resolution Imaging Spectroradiometer) aerosol optical depth (AOD) product and atmospheric circulations derived from National Centers for Environmental Prediction (NCEP) reanalysis data
Values are found in eastern China, i.e. Bohai Gulf, Yangtze River delta, junctional areas of Anhui, Shandong and Henan provinces and most parts of Hubei and Hunan provinces. These regions were recognised as the source of high emissions in October according to Wang and Zhang (2008) and Yang et al (2013). These centres are considered as possible consequences of industrial emissions or agricultural biomass burning that occurs in autumn under certain meteorological conditions

Summary

Introduction

Since aerosols can modulate the radiation budget of the earth-atmosphere system, influence the climate and degrade air quality (Kaufman et al, 2002), they have long been attracting high attentions from scientific community (Twomey, 1977; Rosenfeld et al, 2004; Zhao et al, 2006a, b; Rosenfeld et al, 2007; Li et al, 2011; Koren et al, 2012; Zhao et al, 2012, 2013a, b; Chen et al, 2014). Among the multifaceted problems related to air pollution, favourable weather conditions are a factor that should not be ignored (Zhao et al, 2010; Xu et al, 2011). The characteristics of regional air quality depend on many complex elements, the major contributors are the emission of the pollutants and favourable largescale meteorological conditions The anthropogenic emissions of widespread pollutant sources are quasi-stable in east-

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