CCN activation and cloud processing in sectional aerosol models with low size resolution

[摘要] We investigate the influence of low size resolution, typical to sectionalaerosol models in large scale applications, on cloud droplet activation andcloud processing of aerosol particles. A simplified cloud model with fiveapproaches to determine the fraction of activated particles is compared witha detailed reference model under different atmospheric conditions. Ingeneral, activation approaches which assume a distribution profile withinthe critical model size sections predict the cloud droplet concentrationmost accurately under clean and moderately polluted conditions. In suchcases, the deviation from the reference simulations is below 15% exceptfor very low updraft velocities. In highly polluted cases, the concentrationof cloud droplets is significantly overestimated due to the inability of thesimplified model to account for the kinetic limitations of the dropletgrowth. Of the profiles examined, taking into account the local shape of theparticle size distribution is the most accurate although in most cases theshape of the profile has little relevance. While the low resolution cloudmodel cannot reproduce the details of the out-of-the-cloud aerosol sizedistribution, it captures well the amount of sulphate produced inaqueous-phase reactions as well as the distribution of the sulphate betweenthe cloud droplets. Overall, the simplified cloud model with low sizeresolution performs well for clean and moderately polluted regions thatcover most of the Earth's surface and is therefore suitable for large scalemodels. It can, however, show uncertainties in areas with strong pollution from anthropogenic sources.

[学科分类] 大气科学