Abstract
Abstract. Wet processes, including aqueous-phase chemistry, wet scavenging, and wet surface uptake during dry deposition, are important for global modeling of aerosols and aerosol precursors. In this study, we improve the treatments of these wet processes in the Goddard Earth Observing System with chemistry (GEOS-Chem) v12.6.0, including pH calculations for cloud, rain, and wet surfaces, the fraction of cloud available for aqueous-phase chemistry, rainout efficiencies for various types of clouds, empirical washout by rain and snow, and wet surface uptake during dry deposition. We compare simulated surface mass concentrations of aerosols and aerosol precursors with surface monitoring networks over the United States, European, Asian, and Arctic regions, and show that model results with updated wet processes agree better with measurements for most species. With the implementation of these updates, normalized mean biases (NMBs) of surface nitric acid, nitrate, and ammonium are reduced from 78 %, 126 %, and 45 % to 0.9 %, 15 %, and 4.1 % over the US sites, from 107 %, 127 %, and 90 % to −0.7 %, 4.2 %, and 16 % over European sites, and from 121 %, 269 %, and 167 % to −21 %, 37 %, and 86 % over Asian remote region sites. Comparison with surface measured SO2, sulfate, and black carbon at four Arctic sites indicated that those species simulated with the updated wet processes match well with observations except for a large underestimate of black carbon at one of the sites. We also compare our model simulation with aircraft measurement of nitric acid and aerosols during the Atmospheric Tomography Mission (ATom)-1 and ATom-2 periods and found a significant improvement of modeling skill of nitric acid, sulfate, and ammonium in the Northern Hemisphere during wintertime. The NMBs of these species are reduced from 163 %, 78 %, and 217 % to −13 %, −1 %, and 10 %, respectively. The investigation of impacts of updated wet process treatments on surface mass concentrations indicated that the updated wet processes have strong impacts on the global means of nitric acid, sulfate, nitrate, and ammonium and relative small impacts on the global means of sulfur dioxide, dust, sea salt, black carbon, and organic carbon.
Highlights
Aqueous-phase chemistry, wet scavenging, and wet surface uptake during dry deposition are the three major atmospheric wet processes for aerosols and aerosol precursors
To investigate the impacts of updated wet processes on global simulation of aerosols and aerosol precursors, we run GEOS-Chem for three cases: (1) standard Geos-Chem version 12.6.0, called GC12; (2) the same as case GC12 except using wet scavenging described in the work of Luo et al (2019), and this case is named L2019; (3) the same as the case L2019 except considering the updated wet processes described in Sect. 2, and this case is called WETrev
Other emissions are produced by the default setting of HEMCO (Keller et al, 2014) for all simulations presented in this work
Summary
Aqueous-phase chemistry, wet scavenging, and wet surface uptake during dry deposition are the three major atmospheric wet processes for aerosols and aerosol precursors. Luo et al (2019), L2019 hereafter, updated the GEOS-Chem wet scavenging scheme by using the Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA2) spatially and temporally varying cloud and rainwater to replace the assumption of fixed in-cloud condensation water (ICCW) in the GEOS-Chem rainout parameterization and by using new empirical rates for nitric acid and water-soluble aerosols in washout These changes together reduced the normalized mean biases (NMBs) of simulated nitric acid, nitrate, and ammonium mass concentrations at the United States’ surface monitoring networks from 145 %, 168 %, and 81 % to 24 %, 25 %, and 13 %, respectively. We further update the treatments of wet processes (aqueous chemistry, wet scavenging, and wet surface uptake during dry deposition) in GEOS-Chem and evaluate comprehensively simulated major inorganic aerosol precursors (sulfur dioxide, nitric acid, and ammonia) and aerosols (sulfate, nitrate, ammonium, black carbon, and organic carbon) by comparison with a large set of in situ observations. We assume the pH values at wet surface are 7 for land, 8.2 for ocean, and 5.4 for snow in this work
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