Modelling the formation and composition of secondary organic aerosol from α- and β-pinene ozonolysis using MCM v3

[摘要] The formation and detailed composition of secondary organic aerosol (SOA)from the gas phase ozonolysis of α- and β-pinene has beensimulated using the Master Chemical Mechanism version 3(MCM v3), coupled with a representation of gas-to-aerosol transfer ofsemivolatile and involatile oxygenated products. A kinetics representation,based on equilibrium absorptive partitioning of ca. 200 semivolatileproducts, was found to provide an acceptable description of the final massconcentrations observed in a number of reported laboratory and chamberexperiments, provided partitioning coefficients were increased by about twoorders of magnitude over those defined on the basis of estimated vapourpressures. This adjustment is believed to be due, at least partially, to theeffect of condensed phase association reactions of the partitioningproducts. Even with this adjustment, the simulated initial formation of SOAwas delayed relative to that observed, implying the requirement for theformation of species of much lower volatility to initiate SOA formation. Theinclusion of a simplified representation of the formation and gas-to-aerosoltransfer of involatile dimers of 22 bi- and multifunctional carboxylic acids(in addition to the absorptive partitioning mechanism) allowed a muchimproved description of SOA formation for a wide range of conditions. Thesimulated SOA composition recreates certain features of the productdistributions observed in a number of experimental studies, but implies animportant role for multifunctional products containing hydroperoxy groups(i.e. hydroperoxides). This is particularly the case for experiments inwhich 2-butanol is used to scavenge OH radicals, because[HO₂]/[RO₂] ratios are elevated in such systems. The optimizedmechanism is used to calculate SOA yields from α- and β-pineneozonolysis in the presence and absence of OH scavengers,and as a function of temperature.

[学科分类] 大气科学