Characterization of Secondary Organic Aerosols (SOA) from oxidation of biogenic volatile organic compounds (VOCs) using stable isotopes

Recently it was shown that concurrent measurements of the mixing ratio and δ13C values of atmospheric volatile organic compounds (VOCs) can be used to provide information on the extent of chemical processing these VOCs have undergone in the troposphere (Rudolph et al., 2003). As an extension to this approach, we combine the measurement of gas and particulate phase carbon isotope compositions to study the formation of secondary organic aerosol (SOA) from the ozonolysis reaction of different monoterpenes. Different monoterpenes (α-pinene, β-pinene and limonene) and ozone were injected in to a 1.5 m3 indoor chamber and let to react without the presence of light and OH scavenger under dry conditions. Gas phase samples were collected in MiniVac canisters (400 ml), at a time interval of 30 min. Aerosol samples were collected on quartz fiber filters (Pallflex® Filters) at a flow rate of 9.5 l/min for 3 h. All filters were pretreated at a temperature of 800 °C overnight before sampling. A customized sample pre-concentration system was used for gas phase samples to concentrate the VOC before injecting to a gas chromatograph (Agilent Technologies) coupled to an isotope ratio mass spectrometer (IsoPrime) via a combustion interface (GC-C-IRMS). Prior to the isotopic measurement individual monoterpenes were positively identified using a quadruple mass spectrometer attached to the Gas chromatograph. δ13C of total SOA was measured using an elemental analyzer coupled to the isotope ratio mass spectrometer. In general, the δ13C of SOA formed from ozonolysis of β -pinene was slightly lower than δ13C of the precursor. The general variability in the isotopic composition of SOA from different monoterpenes and the change in isotopic composition of the gas phase monoterpenes during the ozonolysis experiment will be discussed. Reference Rudolph, J., Anderson, R.S., Czapiewski, K.V., Czuba, E., Ernst, D., Gillespie, T., Huang, L., Rigby, C., & Thompson, A.E. (2003). The stable carbon isotope ratio of biogenic emissions of isoprene and the potential use of stable isotope ratio measurements to study photochemical processing of isoprene in the atmosphere Journal of Atmospheric Chemistry, 44 (1), 39-55