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Integrating biomass, sulphate and sea-salt aerosol responses into a microphysical chemical parcel model: implications for climate studies

Ghosh, S., Smith, M.H. and Rap, A. (2007) Integrating biomass, sulphate and sea-salt aerosol responses into a microphysical chemical parcel model: implications for climate studies. Philosophical Transactions of the Royal Society A: Mathematical, 365 (1860). pp. 2659-2674. ISSN 1471-2962

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Abstract

Aerosols are known to influence significantly the radiative budget of the Earth. Although the direct effect (whereby aerosols scatter and absorb solar and thermal infrared radiation) has a large perturbing influence on the radiation budget, the indirect effect (whereby aerosols modify the microphysical and hence the radiative properties and amounts of clouds) poses a greater challenge to climate modellers. This is because aerosols undergo chemical and physical changes while in the atmosphere, notably within clouds, and are removed largely by precipitation. The way in which aerosols are processed by clouds depends on the type, abundance and the mixing state of the aerosols concerned. A parametrization with sulphate and sea-salt aerosol has been successfully integrated within the Hadley Centre general circulation model (GCM). The results of this combined parametrization indicate a significantly reduced role, compared with previous estimates, for sulphate aerosol in cloud droplet nucleation and, consequently, in indirect radiative forcing. However, in this bicomponent system, the cloud droplet number concentration, Nd (a crucial parameter that is used in GCMs for radiative transfer calculations), is a smoothly varying function of the sulphate aerosol loading. Apart from sea-salt and sulphate aerosol particles, biomass aerosol particles are also present widely in the troposphere. We find that biomass smoke can significantly perturb the activation and growth of both sulphate and sea-salt particles. For a fixed salt loading, Nd increases linearly with modest increases in sulphate and smoke masses, but significant nonlinearities are observed at higher non-sea-salt mass loadings. This non-intuitive Nd variation poses a fresh challenge to climate modellers.

Item Type: Article
Copyright, Publisher and Additional Information: © 2007 the author. This is an author produced version of a paper published in Philosophical Transactions of the Royal Society A-Mathematical Physical and Engineering Sciences. Uploaded in accordance with the publisher's self-archiving policy. Openly available from Nov 2008.
Academic Units: The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds)
Depositing User: Sherpa Assistant
Date Deposited: 02 Nov 2007 12:39
Last Modified: 08 Feb 2013 17:05
Published Version: http://dx.doi.org/10.1098/rsta.2007.2082
Status: Published
Publisher: Royal Society Publishing
Refereed: Yes
Identification Number: 10.1098/rsta.2007.2082
URI: http://eprints.whiterose.ac.uk/id/eprint/3457

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