Modeling the influence of chain length on secondary organic aerosol (SOA) formation via multiphase reactions of alkanes

[摘要] Secondary organic aerosol (SOA) from diesel fuel is known to besignificantly sourced from the atmospheric oxidation of aliphatichydrocarbons. In this study, the formation of linear alkane SOA waspredicted using the Unified Partitioning Aerosol Phase Reaction (UNIPAR)model that simulated multiphase reactions of hydrocarbons. In the model, theformation of oxygenated products from the photooxidation of linear alkaneswas simulated using a nearly explicit gas kinetic mechanism. Autoxidationpaths integrated with alkyl peroxy radicals were added to the MasterChemical Mechanism v3.3.1 to improve the prediction of low-volatilityproducts in the gas phase and SOA mass. The resulting gas products were thenlumped into volatility- and reactivity-based groups that are linked to mass-basedstoichiometric coefficients. The SOA mass in the UNIPAR model is producedvia three major pathways: partitioning of gaseous oxidized products ontoboth the organic and wet inorganic phases, oligomerization in the organic phase,and reactions in the wet inorganic phase (acid-catalyzed oligomerization andorganosulfate formation). The model performance was demonstrated for SOAdata that were produced through the photooxidation of a homologous series oflinear alkanes ranging from C9–C15 under varying environments (NO x levels and inorganic seed conditions) in a large outdoor photochemical smogchamber. The product distributions of linear alkanes were mathematicallypredicted as a function of carbon number using an incremental volatilitycoefficient (IVC) to cover a wide range of alkane lengths. The prediction ofalkane SOA using the incremental volatility-based product distributions,which were obtained with C9–C12 alkanes, was evaluated for C13and C15 chamber data and further extrapolated to predict the SOA from longer-chain alkanes ( ≥  C15) that can be found in diesel. The model simulationof linear alkanes in diesel fuel suggests that SOA mass is mainly producedby alkanes C15 and higher. Alkane SOA is insignificantly impacted by thereactions of organic species in the wet inorganic phase due to thehydrophobicity of products but significantly influenced by gas–particlepartitioning.

[学科分类] 医学（综合）