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.