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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 12, issue 20
Atmos. Chem. Phys., 12, 9479–9504, 2012
https://doi.org/10.5194/acp-12-9479-2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 12, 9479–9504, 2012
https://doi.org/10.5194/acp-12-9479-2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 22 Oct 2012

Research article | 22 Oct 2012

Global simulations of nitrate and ammonium aerosols and their radiative effects

L. Xu and J. E. Penner L. Xu and J. E. Penner
  • Department of Atmospheric, Oceanic and Space Science, University of Michigan, Ann Arbor, Michigan, USA

Abstract. We examine the formation of nitrate and ammonium on five types of externally mixed pre-existing aerosols using the hybrid dynamic method in a global chemistry transport model. The model developed here predicts a similar spatial pattern of total aerosol nitrate and ammonium to that of several pioneering studies, but separates the effects of nitrate and ammonium on pure sulfate, biomass burning, fossil fuel, dust and sea salt aerosols. Nitrate and ammonium boost the scattering efficiency of sulfate and organic matter but lower the extinction of sea salt particles since the hygroscopicity of a mixed nitrate-ammonium-sea salt particle is less than that of pure sea salt. The direct anthropogenic forcing of particulate nitrate and ammonium at the top of the atmosphere (TOA) is estimated to be −0.12 W m−2. Nitrate, ammonium and nitric acid gas also affect aerosol activation and the reflectivity of clouds. The first aerosol indirect forcing by anthropogenic nitrate (gas plus aerosol) and ammonium is estimated to be −0.09 W m−2 at the TOA, almost all of which is due to condensation of nitric acid gas onto growing droplets (−0.08 W m−2).

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