The dominant mechanism of the explosive rise of PM2.5 after significant pollution emissions reduction in Beijing from 2017 to the COVID-19 pandemic in 2020

摘要: Abstract The Chinese government implemented strict emission reduction measures of air pollution between 2013 and 2017. However, from the winter 2017 until February 2020, during COVID-19 pandemic, twenty explosive rise (ER) events PM2.5 mass in twelve heavy aerosol episodes (HPEs) still appeared Beijing its vicinity (BIV). To explore controlling mechanism for ER under condition drastically reduced emissions, vertical structure meteorological elements by L-band second-level sounding properties Lidar were investigated associating with analysis surface concentration mass, main precursor gases, as well black carbon (BC) seven-wavelength Aethalometer. planetary boundary layer height (BLH) was also estimated together an unfavorable index (PLAM) that can quantify impact conditions to cause change concentration. results suggested reoccurrence's fundamental is emissions have not yet fallen sufficiently a level decouple HPEs conditions. During period, BLH dropped significantly. fact PM2.5, increased almost similar proportion, indicating caused accumulation dominant reason phenomenon compared chemical conversion factor. two-way feedback effect further worsened typically interpreted 54%–93% ER. An HPE starting 8 Feb. 2020 period underwent one worst conditions, quantified PLAM, BIV since 2013. average only about 66% 2016. It shows substantial reduces primarily before when facing equivalent These combined suggest China's continuous efforts reduce proceed right direction achieved desired results.