Global modelling of secondary organic aerosol in the troposphere: a sensitivity analysis

[摘要] A global 3-dimensional chemistry/transport model able to describeO₃, NO_x, Volatile Organic Compounds (VOC), sulphur andNH₃ chemistry has been extended to simulate the temporal and spatial distribution of primary and secondary carbonaceous aerosols in the tropospherefocusing on Secondary Organic Aerosol (SOA) formation. A number of global simulationshave been performed to determine a possible range of annual global SOA production andinvestigate uncertainties associated with the model results. The studied uncertainties in theSOA budget have been evaluated to be in decreasing importance: the potentially irreversiblesticking of the semi-volatile compounds on aerosols, the enthalpy of vaporization of thesecompounds, the partitioning of SOA on non-carbonaceous aerosols, the conversion ofaerosols from hydrophobic to hydrophilic, the emissions of primary carbonaceous aerosols,the chemical fate of the first generation products and finally the activity coefficient of thecondensable species. The large uncertainties associated with the emissions of VOC and theadopted simplification of chemistry have not been investigated in this study. Although not allsources of uncertainties have been investigated, according to our calculations, the abovefactors within the experimental range of variations could result to an overall uncertainty ofabout a factor of 20 in the global SOA budget. The global annual SOA production frombiogenic VOC might range from 2.5 to 44.5 Tg of organic matter per year, whereas that fromanthropogenic VOC ranges from 0.05 to 2.62 Tg of organic matter per year. These estimatescan be considered as a lower limit, since partitioning on coarse particles like nitrate, dust orsea-salt, together with the partitioning and the dissociation of the semi-volatile products inaerosol water has been neglected. Comparison of model results to observations, whereavailable, shows a better agreement for the upper budget estimates than for the lower ones.

[学科分类] 大气科学