Abstract
Abstract. Currently, mitigating severe particle pollution in autumn and winter is the key to further improving the air quality of China. The source contributions and transboundary transport of fine particles (PM2.5) in pollution episodes are closely related to large-scale or synoptic-scale atmospheric circulation. How to effectively reduce emissions to control haze pollution under different synoptic conditions is rarely reported. In this study, we classify the synoptic conditions over central China from 2013 to 2018 by using Lamb–Jenkinson method and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Final (FNL) operational global analysis data. The effectiveness of emission control to reduce PM2.5 pollution during winter haze episodes under potential synoptic controls is simulated by GEOS-Chem model. Among the 10 identified synoptic patterns, four types account for 87 % of the total pollution days. Two typical synoptic modes are characterized by low surface wind speed and stable weather conditions or high relative humidity (A or C type) over central China due to a high-pressure system or a southwest trough and low-pressure system, blocking pollutants dispersion. Sensitivity simulations show that these two heavy pollution processes are mainly contributed by local emission sources with ∼82 % for A type and ∼85 % for C type, respectively. The other two patterns lead to pollution of transport characteristics affected by northerly or southerly winds (NW or SW type), carrying air pollution from northern or southern China to central China. The contribution of pollution transmission from northern and southern China is 36.9 % and 7.6 %, respectively of PM2.5, and local emission sources contribute 41 % and 69 %, respectively. We also estimate the effectiveness of emission reduction in these four typical severe pollution synoptic processes. By only reducing SO2 and NOx emission and not controlling NH3, the enhanced nitrate counteracts the effect of sulfate reduction on PM2.5 mitigation, with a less than 4 % decrease in PM2.5. In addition, to effectively mitigate haze pollution of NW- and SW-type synoptic-controlled episodes, local emission control actions should be in coordination with regional collaborative actions.
Highlights
The regional pollution of fine particles (PM2.5) has attracted worldwide attention from the public and in the scientific community (Cheng et al, 2016; Li et al, 2017c; Lin et al, 2018; Bi et al, 2019) due to its detrimental effect on visibility (Wang et al, 2020) and public health (Agarwal et al, 2017; Zhang et al, 2017)
It is affected by the southerly airflow, which could be conducive to the transport of air pollutants formed over southern China to central China
The extremely severe and persistent PM2.5 pollution episodes are attributed to adverse synoptic conditions in addition to high precursor emissions
Summary
The regional pollution of fine particles (PM2.5) has attracted worldwide attention from the public and in the scientific community (Cheng et al, 2016; Li et al, 2017c; Lin et al, 2018; Bi et al, 2019) due to its detrimental effect on visibility (Wang et al, 2020) and public health (Agarwal et al, 2017; Zhang et al, 2017). Severe particle pollution still occurs frequently in autumn and winter, which is the major reason restricting the PM2.5 from reaching the national standard. Researching how to effectively reduce emissions in autumn and winter is the key to mitigating haze pollution in China. The outbreak, persistence, and dissipation of particle pollution generally depends on meteorological conditions and regional synoptic patterns controlled by the large-scale or synoptic-scale atmospheric circulation (Chuang et al, 2008; Zhang et al, 2012; Russo et al, 2014; Zheng et al, 2015; Shu et al, 2017; Li et al, 2019)
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