Sulfur, sea salt, and radionuclide aerosols in GISS ModelE

Abstract

[1] We simulate a suite of aerosols in the new GISS ModelE GCM: present-day sulfur species and the natural species sea salt, radionuclides 7 Be (stratospheric source), and 210 Pb (derived from 222 Rn from soils). The natural species are used to test the model and to help diagnose the anthropogenic sulfur species. Model improvements over previous versions include increased vertical resolution, addition of a stratiform dissolved species budget (DSB), better tracer coupling to the boundary layer, and an improved relative humidity-dependent radiative scheme. The DSB reduces the loads of most soluble species since it increases stratiform precipitation scavenging. We compare the model with extensive surface and aircraft concentration measurements in the troposphere and stratosphere. We compare three different formulations of the 222 Rn emissions and find that a scheme with reduced radon flux at high latitudes of the Northern Hemisphere for all seasons gives the best 210 Pb results. Although the 222 Rn emissions appear to be approximately the right order of magnitude, model 210 Pb is too large. Conversely, our 7 Be source is too small (since concentrations in the upper troposphere and stratosphere are deficient), while the 7 Be surface concentrations are as observed. These radionuclide results suggests that model scavenging (by moist convection) is deficient. Our new model uses increased natural sulfur emissions; however, the DSB causes sulfate to be generally less than observed and indicates a need for additional sulfur oxidation mechanisms. Model radiative forcing for sulfate and sea salt are À0.54 and À1.1 W m À2 , respectively. The anthropogenic sulfate forcing is À0.25 W m À2 , less than the À0.68 W m À2 in our previous model mainly owing to an 18% decrease in industrial emissions.

Influence of model resolution on the atmospheric transport of <sup>10</sup>Be

“…This simplified emission scheme has successfully been used by numerous modelling studies (e.g. Feichter et al, 1991;Liu et al, 2001;Koch et al, 2006). 210 Pb has a similar geochemical behaviour to 10 Be or 7 Be.…”

“…Pedro et al, 2011) require the use of a global model or at least one including one hemisphere. Comparison with observations has shown that they are much more sensitive to uncertainties in scavenging and atmospheric transport than short-lived tracers emitted from Earth's surface (Brost et al, 1996;Koch et al, 2006;Liu et al, 2001). Optimally a model version including the middle atmosphere would be used, describing full stratospheric dynamics and allowing for a better representation of the Brewer-Dobson circulation and hence tracer transport.…”

Influences of in-cloud aerosol scavenging parameterizations on aerosol concentrations and wet deposition in ECHAM5-HAM

“…7 Be and 210 Pb have been simulated in global models, and used as passive tracers for the validation of deposition parameterizations (e.g., Brost et al, 1991;Liu et al, 2001;Feichter et al, 1991;Koch et al, 1996Koch et al, , 2006. Recently, simulation of 7 Be and 210 Pb have been introduced into the ECHAM5-HAM (Heikkilä et al, 2008(Heikkilä et al, , 2009).…”

“…The production rates for 7 Be were taken from Masarik and Beer (1999). The 210 Pb/radon source is from soils and was taken to be 1 atoms cm −2 s −1 , following Feichter et al (1991);Liu et al (2001); Koch et al (2006). 7 Be and 210 Pb are not explicitly distributed into the aerosol modes of the ECHAM5-HAM.…”

Aerosol distribution over Europe: a model evaluation study with detailed aerosol microphysics

“…Feichter et al, 1996;Koch et al, 2006; with different degrees of complexity concerning oxidant availability, aqueous phase chemistry, dry and wet deposition. Major efforts have been made in recent years to improve atmospheric aerosol modeling on the global and regional scale.…”