Climate anomalies contributed to the rebound of PM2.5 in 2018 under intensified regional air pollution preventions.

ABSTRACT

Rigorous air pollution managements since 2013 resulted in decreasing trend in fine particulate matter (PM2.5) in China. Regional air pollution prevention measures were extra implemented in the "2 + 26" region since 2017. However, haze pollution dramatically rebounded in the winter of 2018. Both of the observed analyses and the numerical results (basing on a global 3-D chemical transport model) demonstrated that, although intensified prevention measures existed, atmospheric circulation and local meteorological conditions still significantly influenced the variation in haze pollution. The simulated PM2.5 concentrations (with fixed emissions) driven by meteorology in 2018 were 12-15% higher than those with atmospheric circulations in 2017 both under a low and a high emission level, close to the observed 10% PM2.5 rebound. In 2018, positive sea ice anomalies around Beaufort Sea and "triple pattern" anomalies of sea surface temperature in the North Pacific and North Atlantic enhanced the anomalous anticyclonic circulations over the air-polluted region, and thus resulted in minimum surface wind speed during 1979-2018 and 16.8% shallower boundary layer than those in 2017. In the stagnated air of winter 2018, the transported dispersion of pollutant particles was weakened, however more secondary aerosols were produced by enhanced chemical reactions, which jointly contributed to the PM2.5 rebound in 2018.