Journal Article
Atmospheric Chemistry and Physics, vol. 20, iss. 20, pp. 12265-12284, 2020
Authors
Ruqian Miao, Qi Chen, Yan Zheng, Xi Cheng, Yele Sun, Paul I. Palmer, Manish Shrivastava, Jianping Guo, Qiang Zhang, Yuhan Liu, Zhaofeng Tan, Xuefei Ma, Shiyi Chen, Limin Zeng, Keding Lu, Yuanhang Zhang
Abstract
Abstract. High concentrations of PM2.5 (particulate matter
with an aerodynamic diameter less than 2.5 µm) in China have caused
severe visibility degradation. Accurate simulations of PM2.5 and its
chemical components are essential for evaluating the effectiveness of
pollution control strategies and the health and climate impacts of air
pollution. In this study, we compared the GEOS-Chem model simulations with
comprehensive datasets for organic aerosol (OA), sulfate, nitrate, and
ammonium in China. Model results are evaluated spatially and temporally
against observations. The new OA scheme with a simplified secondary organic
aerosol (SOA) parameterization significantly improves the OA simulations in
polluted urban areas, highlighting the important contributions of
anthropogenic SOA from semivolatile and intermediate-volatility organic
compounds. The model underestimates sulfate and overestimates nitrate for
most of the sites throughout the year. More significant underestimation of
sulfate occurs in winter, while the overestimation of nitrate is extremely
large in summer. The model is unable to capture some of the main features in
the diurnal pattern of the PM2.5 chemical components, suggesting
inaccuracies in the presented processes. Potential model adjustments that
may lead to a better representation of the boundary layer height, the
precursor emissions, hydroxyl radical concentrations, the heterogeneous
formation of sulfate and nitrate, and the wet deposition of nitric acid and
nitrate have been tested in the sensitivity analysis. The results show that
uncertainties in chemistry perhaps dominate the model biases. The proper
implementation of heterogeneous sulfate formation and the good estimates of
the concentrations of sulfur dioxide, hydroxyl radical, and aerosol liquid
water are essential for the improvement of the sulfate simulation. The
update of the heterogeneous uptake coefficient of nitrogen dioxide
significantly reduces the modeled concentrations of nitrate. However, the
large overestimation of nitrate concentrations remains in summer for all
tested cases. The possible bias in the chemical production and the wet
deposition of nitrate cannot fully explain the model overestimation of
nitrate, suggesting issues related to the atmospheric removal of nitric acid
and nitrate. A better understanding of the atmospheric nitrogen budget, in
particular, the role of the photolysis of particulate nitrate, is needed for
future model developments. Moreover, the results suggest that the remaining
underestimation of OA in the model is associated with the underrepresented
production of SOA.
