Control of fine particulate nitrate during severe winter haze in “2+26” cities

Abstract

The “2+26” cities, suffering the most severe winter haze pollution, have been the key region for air quality improvement in China. Increasing prominent nitrate pollution is one of the most challenging environmental issues in this region, necessitating development of an effective control strategy. Herein, we use observations, and state-of-the-art model simulations with scenario analysis and process analysis to quantify the effectiveness of the future SO2-NOX-VOC-NH3 emission control on nitrate pollution mitigation in “2+26” cities. Focusing on a serious winter haze episode, we find that limited NOX emission reduction alone in the short-term period is a less effective choice than VOC or NH3 emission reduction alone to decrease nitrate concentrations, due to the accelerated NOX-HNO3 conversion by atmospheric oxidants and the enhanced HNO3 to NO3− partition by ammonia, although deep NOX emission reduction is essential in the long-term period. The synergistic NH3 and VOC emission control is strongly recommended, which can counteract the adverse effects of nonlinear photochemistry and aerosol chemical feedback to decrease nitrate more. Such extra benefits will be reduced if the synergistic NH3 and VOC reduction is delayed, and thus reducing emission of multiple precursors is urgently required for the effective control of increasingly severe winter nitrate pollution in “2+26” cities.