Soot versus cloud condensation nuclei

If aerosol particles are more numerous and also soluble, for example consist of ammoniumsulfate ((NH4)2 SO4) formed from the air pollution gases sulphur dioxide (SO2) and ammonia (NH3), clouds would contain more and smaller droplets per unit volume at the same circulation conditions (see also section 2.6). These clouds scatter more sun-light (see equation 2.1) and their albedo would increase, counteracting an enhanced greenhouse effect, if their height would not change. If polluted air - as is normally the case - would also contain more soot (black carbon) the clouds forming in such air would be less scattering, look darker when viewed from above and below. Only for optically not very thick clouds would the increased light scattering effect dominate under such conditions. Hence, soot will damp the clouds' ability to mask effects of an enhanced greenhouse effect. Therefore addition of soot would contribute in the cloud free atmosphere to the warming but dampen the indirect effect of air pollution on cloud albedo, certainly overriding it for optically thick clouds.

Reducing soot content of the air, a health issue anyway, has also a potential to reduce global warming.

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