A GCM study of organic matter in marine aerosol and its potential contribution to cloud drop activation

[摘要] With the global aerosol-climate model ECHAM5-HAM we investigate thepotential influence of organic aerosol originating from the ocean on aerosolmass and chemical composition and the droplet concentration and size ofmarine clouds. We present sensitivity simulations in which the uptake oforganic matter in the marine aerosol is prescribed for each aerosol modewith varying organic mass and mixing state, and with a geographicaldistribution and seasonality similar to the oceanic emission of dimethylsulfide. Measurements of aerosol mass, aerosol chemical composition andcloud drop effective radius are used to assess the representativity of themodel initializations. Good agreement with the measurements is obtained whenorganic matter is added to the Aitken, accumulation and coarse modessimultaneously. Representing marine organics in the model leads to highercloud drop number concentrations and thus smaller cloud drop effectiveradii, and this improves the agreement with measurements. The mixing stateof the organics and the other aerosol matter, i.e. internal or externaldepending on the formation process of aerosol organics, is an importantfactor for this. We estimate that globally about 75 Tg C yr⁻¹ oforganic matter from marine origin enters the aerosol phase, with comparablecontributions from primary emissions and secondary organic aerosolformation.

[学科分类] 大气科学