Global modelling of Arctic aerosol
We use a global model of size-resolved aerosol microphysics to evaluate our understanding of the processes that control Arctic aerosol, focussing on the transition from Arctic haze in spring to cleaner conditions in summer. Observations show a transition from an accumulation mode-dominated aerosol in spring to one dominated by Aitken and nucleation mode particles in summer. We find that remote Arctic aerosol is very sensitive to the model treatment of wet removal. In order to simulate the high accumulation mode concentrations typical of winter and spring it was necessary to substantially reduce the scavenging of these particles during transport. The resulting increases in accumulation mode lead to improvement in the modelled Aitken mode particle concentrations (which fall, due to increased scavenging in the free troposphere) and produce aerosol optical depths in good agreement with observations.
