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Journal article

Brightening of the global cloud field by nitric acid and the associated radiative forcing

Makkonen R, Romakkaniemi S, Kokkola H, Stier P, Räisänen P, Rast S, Feichter J, Kulmala M, Laaksonen A ...see all

Atmospheric Chemistry and Physics, vol. 12, issue 16 (2012) pp. 7625-7633

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Abstract

Clouds cool Earth's climate by reflecting 20% of the incoming solar
energy, while also trapping part of the outgoing radiation. The effect
of human activities on clouds is poorly understood, but the present-day
anthropogenic cooling via changes of cloud albedo and lifetime could be
of the same order as warming from anthropogenic addition in CO2. Soluble
trace gases can increase water condensation to particles, possibly
leading to activation of smaller aerosols and more numerous cloud
droplets. We have studied the effect of nitric acid on the aerosol
indirect effect with the global aerosol-climate model ECHAM5.5-HAM2.
Including the nitric acid effect in the model increases cloud droplet
number concentrations globally by 7%. The nitric acid contribution to
the present-day cloud albedo effect was found to be -0.32 W m(-2) and to
the total indirect effect -0.46 W m(-2). The contribution to the cloud
albedo effect is shown to increase to -0.37 W m(-2) by the year 2100, if
considering only the reductions in available cloud condensation nuclei.
Overall, the effect of nitric acid can play a large part in aerosol
cooling during the following decades with decreasing SO2 emissions and
increasing NOx and greenhouse gases.

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