LARGE CONTRIBUTION OF ORGANIC AEROSOLS TO CLOUD-CONDENSATION-NUCLEI CONCENTRATIONS

THE albedo and radiative properties of marine stratus clouds are determine largely by the number density of cloud condensation nuclei (CCN) over the oceans. Modelling studies have suggested that most of these nuclei are sulphate aerosols derived from both anthropogenic and natural sources1. Here we present evidence that organic aerosols also play a key role in cloud nucleation. We determine the relative contributions of sulphate and organic aerosols to CCN concentrations at a marine site known to be influenced by anthropogenic emissions, and find that organic aerosols account for the major part of both the total aerosol number concentration and the CCN fraction. Thus, in regions that are affected by anthropogenic pollutants, organic aerosols may play at least as important a role as sulphate aerosols in determining the climate effect of clouds.