Abstract
Airborne aerosols reduce surface solar radiation through light scattering and absorption (aerosol direct effects, ADE), influence regional meteorology, and further affect atmospheric chemical reactions and aerosol concentrations. Several studies have revealed that the inhibition of turbulence and the increase in atmospheric stability induced by ADE increases surface primary aerosol concentration, but the pathway of ADE impacts on secondary aerosol is still unclear. In this study, the two-way coupled WRF-CMAQ with integrated process analysis was applied to explore how ADE impacts secondary aerosol formation through changes in atmospheric dynamics and photolysis processes. Meteorological and air quality fields in Jing-Jin-Ji area (denoted JJJ, including Beijing, Tianjin and Hebei Province in China) in January and July 2013 were simulated to represent winter and summer conditions, respectively. Two pathways of ADE impacts on aerosol concentration, i.e., photolysis modification and atmospheric dynamics modification were estimated separately through scenario analysis. The results show that solar radiation is the restricting factor in winter, and the formation of sulfate is sensitive to the perturbation of solar radiation. While in summer, availability of gaseous precursors primarily dictates the levels of secondary aerosol concentrations. ADE through the attenuation of photolysis inhibits secondary aerosol formation during winter and promotes secondary aerosol formation during summer. The seasonal differences are attributed to change of effective actinic flux in winter and summer determined by aerosol optical depth, solar zenith angles, and single scattering albedo. ADE through dynamic processes is the dominant process influencing surface secondary aerosol formation due to the accumulation of gaseous precursors. Different from sulfate, the surface layer is a net-source of nitrate during winter but a sink during summer. Therefore, ADE promotes nitrate accumulation in winter and reduces nitrate accumulation in summer.
Highlights
Aerosols have long been recognized as a major source of uncertainty in the climate system due to their interaction with solar radiation and clouds (Carslaw et al, 2013;Koch and Del Genio, 2010;Ramanathan et al, 2001;Rosenfeld et al, 2014)
Our results indicate that aerosol direct effects (ADE) affecting sulfate formation through dynamic pathway is a metric of equal, or greater, importance than that of photolysis pathway in both summer and winter
This study quantified the impacts of ADE on PM2.5 using the two-way online coupled meteorology and atmospheric chemistry model (WRF-Community Multiscale Air Quality Modeling System (CMAQ)) with integrated process analysis
Summary
Aerosols have long been recognized as a major source of uncertainty in the climate system due to their interaction with solar radiation and clouds (Carslaw et al, 2013;Koch and Del Genio, 2010;Ramanathan et al, 2001;Rosenfeld et al, 2014). Studies in recent decades have revealed the impact of aerosol direct effects (ADE) on air pollutants (Wang et al, 2014;Xing et al, 2015a;Xing et al, 2016;Ding et al, 2016b;Wang et al, 2013;Wang et al, 2018b;Huang et al, 2018;Wang et al, 2018a;Wang et al, 2015;Hong et al, 2020;Atwater, 1971;Ackerman, 1977;Ramanathan et al, 2001;Wendisch et al, 2008;Grell et al, 2011;Wong et al, 2012;Barbaro et al, 2013). The reduced solar radiation leads to a decrease in temperature (McCormick and Ludwig, 1967). The absorbing aerosols lead to an increased temperature at higher altitude (Ding et al, 2016b). The opposite trend of temperature change between near-surface layer and higher layer in the planetary boundary layer (PBL) is supported by the air temperature from observation in Beijing and global meteorological reanalysis (Huang et al, 2018;Huang and Ding, 2021)
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