Importance of the organic aerosol fraction for modeling aerosol hygroscopic growth and activation: a case study in the Amazon Basin

[摘要] The aerosol in the Amazon basin is dominated throughout the year by organicmatter, for the most part soluble in water. In this modeling study, we showhow the knowledge of water-soluble organic compounds (WSOC) and theassociated physical and chemical properties (e.g. solubility, surfacetension, dissociation into ions) affect the hygroscopic growth andactivation of the aerosol in this area. The study is based on data obtainedduring the SMOCC field experiment carried out in Rondônia, Brazil, overa period encompassing the dry (biomass burning) season to the onset of thewet season (September to mid-November, 2002). The comparison of predictedand measured cloud condensation nuclei (CCN) number concentration shows thatthe knowledge of aerosol WSOC composition in terms of classes of compoundsand of their relative molecular weights and acidic properties may besufficient to predict aerosol activation, without any information onsolubility. Conversely, the lack of knowledge on WSOC solubility leads to ahigh overestimation of the observed diameter growth factors (DGF) by thetheory. Moreover, the aerosol water soluble inorganic species fail to predict bothDGFs and CCN number concentration. In fact, this study shows that a good reproductionof the measured DGF andCCN concentration is obtained if the chemical composition ofaerosol, especially that of WSOC, is appropriately taken into account inthe calculations. New parameterizations for the computed CCN spectra arealso derived which take into account the variability caused by chemicaleffects (surface tension, molecular composition, solubility, degree ofdissociation of WSOC).

[学科分类] 大气科学