Simulation of aromatic SOA formation using the lumping model integrated with explicit gas-phase kinetic mechanisms and aerosol-phase reactions

摘要

The Unified Partitioning-Aerosol phase Reaction (UNIPAR) model has beendeveloped to predict the secondary organic aerosol (SOA) formation throughmultiphase reactions. The model was evaluated with aromatic SOA data producedfrom the photooxidation of toluene and 1,3,5-trimethylbenzene (135-TMB) undervarious concentrations of NO and SO using an outdoorreactor (University of Florida Atmospheric PHotochemical Outdoor Reactor(UF-APHOR) chamber). When inorganic species (sulfate, ammonium and water)are present in aerosol, the prediction of both toluene SOA and 135-TMB SOA,in which the oxygen-to-carbon (O : C) ratio is lower than 0.62, are approachedunder the assumption of a complete organic/electrolyte-phase separation belowa certain relative humidity. An explicit gas-kinetic model was employed toexpress gas-phase oxidation of aromatic hydrocarbons. Gas-phase products aregrouped based on their volatility (6 levels) and reactivity (5 levels) andexploited to construct the stoichiometric coefficient (α)matrix, the set of parameters used to describe the concentrations of organiccompounds in multiphase. Weighting of the α matrix as a functionof NO improved the evaluation of NO effects on aromaticSOA. The total amount of organic matter (OM) is predicted by two modulesin the UNIPAR model: OM by a partitioning process and OM byaerosol-phase reactions. The OM module predicts multiphase reactions oforganic compounds, such as oligomerization, acid-catalyzed reactions, andorganosulfate (OS) formation. The model reasonably simulates SOA formationunder various aerosol acidities, NO concentrations, humidities andtemperatures. Furthermore, the OS fractions in the SOA predicted by the modelwere in good agreement with the experimentally measured OS fractions.