Effectiveness of emission control in reducing PM2.5 pollution in central China during winter haze episodes under various potential synoptic controls

Abstract

Abstract. Currently, mitigating severe particle pollution in autumn and winter is\nthe key to further improving the air quality of China. The source\ncontributions and transboundary transport of fine particles\n(PM 2.5 ) in pollution episodes are closely related to large-scale\nor synoptic-scale atmospheric circulation. How to effectively reduce emissions to control haze pollution under different synoptic\nconditions is\nrarely reported. In this study, we classify the synoptic conditions over\ncentral China from 2013 to 2018 by using Lamb–Jenkinson method and the\nNational Centers for Environmental Prediction/National Center for\nAtmospheric Research (NCEP/NCAR) Final (FNL) operational global analysis data. The effectiveness of\nemission control to reduce PM 2.5 pollution during winter haze episodes\nunder potential synoptic controls is simulated by GEOS-Chem model. Among the\n10 identified synoptic patterns, four types account for 87\u2009% of the total\npollution days. Two typical synoptic modes are characterized by\nlow surface wind speed and stable weather conditions or high relative\nhumidity (A or C type) over central China due to a high-pressure system or a\nsouthwest trough and low-pressure system, blocking pollutants dispersion.\nSensitivity simulations show that these two heavy pollution processes are\nmainly contributed by local emission sources with ∼82 \u2009% for\nA\xa0type and ∼85 \u2009% for C\xa0type, respectively. The other two\npatterns lead to pollution of transport characteristics affected by\nnortherly or southerly winds (NW or SW type), carrying air pollution from\nnorthern or southern China to central China. The contribution of pollution\ntransmission from northern and southern China is 36.9\u2009% and 7.6\u2009%, respectively of PM 2.5 , and\nlocal emission sources contribute 41\u2009% and 69\u2009%, respectively. We also estimate the\neffectiveness of emission reduction in these four typical severe pollution\nsynoptic processes. By only reducing SO 2 and NO x emission and not\ncontrolling NH 3 , the enhanced nitrate counteracts the effect of sulfate\nreduction on PM 2.5 mitigation, with a less than 4\u2009% decrease in\nPM 2.5 . In addition, to effectively mitigate haze pollution of\nNW- and SW-type synoptic-controlled episodes, local emission control actions\nshould be in coordination with regional collaborative actions.