An Aerodyne Aerosol Mass Spectrometer (AMS) has been utilised to provide on-line measurements of the mass spectral signatures and mass size distributions of the oxidation products resulting from irradiating 1,3,5- trimethylbenzene (1,3,5-TMB) and -pinene, separately, in the presence of nitrogen oxide, nitrogen dioxide and propene in a reaction chamber. Mass spectral results indicate that both precursors produce SOA with broadly similar chemi- cal functionality of a highly oxidised nature. However, sig- nificant differences occur in the minor mass spectral frag- ments for the SOA in the two reaction systems, indicating that they have different molecular composition. Nitrogen- containing organic compounds have been observed in the photooxidation products of both precursors, and their for- mation appeared to be controlled by the temporal variabil- ity of NOx. Although the overall fragmentation patterns of the photooxidation products in both systems did not change substantially over the duration of each experiment, the con- tribution of some individual mass fragments to total mass appeared to be influenced by the irradiation time. The ef- fective densities of the 1,3,5-TMB and -pinene SOA parti- cles were determined for various particle sizes using the re- lationship between mobility and vacuum aerodynamic diam- eters. The effective density for the 1,3,5-TMB SOA ranged from 1.35-1.40g/cm 3 , while that for -pinene SOA ranged from 1.29-1.32g/cm 3 . The determined effective densities did not show dependence on irradiation time. Results sug- gest that further chemical processing of SOA takes place in the real atmosphere, as neither the -pinene nor the 1,3,5- TMB experimental results reproduce the right relative prod- uct distribution between carbonyl-containing and multifunc- tional carboxylic acid species measured at ambient locations influenced by aged continental organic aerosols.
A mass spectrometric study of secondary organic aerosols formed from the photooxidation of anthropogenic and biogenic precursors in a reaction chamber
M. Alfarra,D. Paulsen,M. Gysel,A. Garforth,J. Dommen,A. Prévôt,D. Worsnop,U. Baltensperger,H. Coe
Published 2006 in Atmospheric Chemistry and Physics
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- Publication year
2006
- Venue
Atmospheric Chemistry and Physics
- Publication date
2006-11-20
- Fields of study
Chemistry, Environmental Science
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