Global simulations of nitrate and ammonium aerosols and their radiative effects Department of Atmospheric, Oceanic and Space Science, University of Michigan, Ann Arbor, Michigan, USA
22 Oct 2012
Received: 26 March 2012 – Published in Atmos. Chem. Phys. Discuss.: 19 April 2012 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).
Revised: 14 September 2012 – Accepted: 24 September 2012 – Published: 22 October 2012
Citation: Xu, L. and Penner, J. E.: Global simulations of nitrate and ammonium aerosols and their radiative effects, Atmos. Chem. Phys., 12, 9479-9504, doi:10.5194/acp-12-9479-2012, 2012.