Measurements of Secondary Organic Aerosol from Oxidation of Cycloalkenes, Terpenes, and m-Xylene Using an Aerodyne Aerosol Mass Spectrometer
he Aerodyne aerosol mass spectrometer (AMS) was used to characterize physical and chemical properties of secondary organic aerosol (SOA) formed during ozonolysis of cycloalkenes and biogenic hydrocarbons and photooxidation of m-xylene. Comparison of mass and volume distributions from the AMS and differential mobility analyzers yielded estimates of "effective" density of the SOA in the range of 0.64−1.45 g/cm^3, depending on the particular system. Increased contribution of the fragment at m/z 44, CO_2^+ ion fragment of oxygenated organics, and higher "Δ" values, based on ion series analysis of the mass spectra, in nucleation experiments of cycloalkenes suggest greater contribution of more oxygenated molecules to the SOA as compared to those formed under seeded experiments. Dominant negative "Δ" values of SOA formed during ozonolysis of biogenics indicates the presence of terpene derivative structures or cyclic or unsaturated oxygenated compounds in the SOA. Evidence of acid-catalyzed heterogeneous chemistry, characterized by greater contribution of higher molecular weight fragments to the SOA and corresponding changes in "Δ" patterns, is observed in the ozonolysis of α-pinene. Mass spectra of SOA formed during photooxidation of m-xylene exhibit features consistent with the presence of furandione compounds and nitro organics. This study demonstrates that mixtures of SOA compounds produced from similar precursors result in broadly similar AMS mass spectra. Thus, fragmentation patterns observed for biogenic versus anthropogenic SOA may be useful in determining the sources of ambient SOA.
© 2005 American Chemical Society. Received for review December 7, 2004. Revised manuscript received April 27, 2005. Accepted May 19, 2005. This research was funded by the U.S. Environmental Protection Agency Science to Achieve Results (STAR) Program grant number RD-83107501-0, managed by EPA's Office of Research and Development (ORD), National Center for Environmental Research (NCER), U.S. Department of Energy Biological and Environmental Research Program DE-FG03-01ER63099, and by the National Science Foundation grant ATM-0340832. We thank J. D. Allan (UMIST) for fundamental AMS data analysis software, M. R. Canagaratna and T. Onasch (Aerodyne Research, Inc.) for developing the software for ion series analysis of AMS data, and F. Brechtel (Caltech and Brechtel Manufacturing Inc.) for helpful discussions.