Earth system modeling of mercury using CESM2 – Part 1: Atmospheric model CAM6-Chem/Hg v1.0

Abstract

Abstract. Most global atmospheric mercury models use offline and reanalyzed meteorological fields, which has the advantages of higher accuracy and lower computational cost compared to online models. However, these meteorological products need past and/or near-real-time observational data and cannot predict the future. Here, we use an atmospheric component with tropospheric and stratospheric chemistry (CAM6-Chem) of the state-of-the-art global climate model CESM2, adding new species of mercury and simulating atmospheric mercury cycling. Our results show that the newly developed online model is able to simulate the observed spatial distribution of total gaseous mercury (TGM) in both polluted and non-polluted regions with high correlation coefficients in eastern Asia (r=0.67) and North America (r=0.57). The calculated lifetime of TGM against deposition is 5.3 months and reproduces the observed interhemispheric gradient of TGM with a peak value at northern mid-latitudes. Our model reproduces the observed spatial distribution of HgII wet deposition over North America (r=0.80) and captures the magnitude of maximum in the Florida Peninsula. The simulated wet deposition fluxes in eastern Asia present a spatial distribution pattern of low in the northwest and high in the southeast. The online model is in line with the observed seasonal variations of TGM at northern mid-latitudes as well as the Southern Hemisphere, which shows lower amplitude. We further go into the factors that affect the seasonal variations of atmospheric mercury and find that both Hg0 dry deposition and HgII dry/wet depositions contribute to it.