The effect of organic compounds on the growth rate of cloud droplets in marine and forest settings

[摘要] Organic matter represents an important fraction of the fine particle aerosol,yet our knowledge of the roles of organics in the activation of aerosolparticles into cloud droplets is poor. A cloud condensation nucleus (CCN)counter is used to examine the relative growth rates of cloud droplets forcase studies from field measurements on the North Pacific Ocean and in aconiferous forest. A model of the condensational growth of water droplets, onparticles dissolving according to their solubility in water, is used tosimulate the initial scattering of the droplets as they grow in the CCNcounter. Simulations of the growth rates of fine particles sampled in themarine boundary layer of the North Pacific Ocean shows no evidence of naturalmarine organic material contributing to the CCN water uptake but there is anindication of an influence from organics from diesel ship emissions on thesize distribution of sulphate and the ability of these particles to act asCCN. Simulations of the observations of water uptake on biogenic organicaerosol particles sampled in a coniferous forest indicate an impact of theorganic on the water uptake rates, but one that is still smaller than that ofpure sulphate. The existence of organics becomes important in determining thewater uptake as the organic mass increases relative to sulphate. The valuesof the organic component of the hygroscopicity parameter κ thatdescribes the CCN activity were found to be negligible for the marineparticles and 0.02–0.05 for the forest particles.

[学科分类] 大气科学