Removal of PM2.5 and secondary inorganic aerosols in the North China Plain by dry deposition

Abstract

The North China Plain (NCP) has experienced heavy air pollution in the past several decades featured by high levels of fine particulate matter (PM2.5). PM2.5 removal from the atmosphere in the NCP by dry deposition was estimated from 1999 through 2013 using the inferential method, which combined PM2.5 air concentrations retrieved from satellite remote sensing and dry deposition velocities (Vd) calculated using a bulk particle dry deposition model. Dry deposition of the three major inorganic ions in PM2.5, namely NH4+ (ammonium), NO3− (nitrate), and SO42− (sulfate), with their concentrations in 2000 and 2010 obtained from WRF-Chem model simulations, were also investigated considering their important roles in PM2.5 formation and ecosystem health. High levels of modeled and satellite-retrieved PM2.5 air concentrations, the secondary inorganic aerosols (the sum of NH4+, NO3−, and SO42−), and their respective deposition fluxes were identified from the southern NCP to Beijing-Tianjin metropolitans. The deposition fluxes derived from the inferential method and WRF-Chem increased considerably in the 2000s due to rising PM2.5 atmospheric levels across the NCP. The enhancement of dry deposition velocities of PM2.5 and three aerosol species in the NCP were associated nicely with increasing vegetation coverage and wind speed. We show that both air concentrations of PM2.5 and secondary inorganic aerosols and rising dry deposition velocities related to extensive afforestation activities contributed to their deposition fluxes and an inclining trend of PM2.5 removal from the atmosphere.