Simulating the detailed chemical composition of secondary organic aerosol formed on a regional scale during the TORCH 2003 campaign in the southern UK

[摘要] Following on from the companion study (Johnson et al., 2006), aphotochemical trajectory model (PTM) has been used to simulate the chemicalcomposition of organic aerosol for selected events during the 2003 TORCH(Tropospheric Organic Chemistry Experiment) field campaign. The PTMincorporates the speciated emissions of 124 non-methane anthropogenicvolatile organic compounds (VOC) and three representative biogenic VOC, ahighly-detailed representation of the atmospheric degradation of these VOC,the emission of primary organic aerosol (POA) material and the formation ofsecondary organic aerosol (SOA) material. SOA formation was represented bythe transfer of semi- and non-volatile oxidation products from the gas-phaseto a condensed organic aerosol-phase, according to estimated thermodynamicequilibrium phase-partitioning characteristics for around 2000 reactionproducts. After significantly scaling all phase-partitioning coefficients,and assuming a persistent background organic aerosol (both required in orderto match the observed organic aerosol loadings), the detailed chemicalcomposition of the simulated SOA has been investigated in terms ofintermediate oxygenated species in the Master Chemical Mechanism, version3.1 (MCM v3.1). For the various case studies considered, 90% of thesimulated SOA mass comprises between ca. 70 and 100 multifunctionaloxygenated species derived, in varying amounts, from the photooxidation ofVOC of anthropogenic and biogenic origin. The anthropogenic contribution isdominated by aromatic hydrocarbons and the biogenic contribution by α-and β-pinene (which also constitute surrogates for other emittedmonoterpene species). Sensitivity in the simulated mass of SOA to changes inthe emission rates of anthropogenic and biogenic VOC has also beeninvestigated for 11 case study events, and the results have been compared tothe detailed chemical composition data. The role of accretion chemistry inSOA formation, and its implications for the results of the presentinvestigation, is discussed.

[学科分类] 大气科学