Molecular composition of aged secondary organic aerosol generated from a mixture of biogenic volatile compounds using ultrahigh resolution mass spectrometry

I. Kourtchev, J.-F. Doussin, C. Giorio, B. Mahon, E. M. Wilson, N. Maurin, E. Pangui, D. S. Venables, J. C. Wenger, M. Kalberer

Research output: Working paper/PreprintDiscussion paper

Abstract

Field observations over the past decade indicate that a significant fraction of organic
aerosol in remote areas may contain highly oxidised molecules. Aerosol processing or
further oxidation (ageing) of organic aerosol has been suggested to be responsible for
5 their formation through heterogeneous uptake of oxidants and multigenerational oxidation of vapours by OH radicals. In this study we investigated the influence of several
ageing processes on the molecular composition of secondary organic aerosols (SOA)
using direct infusion and liquid chromatography ultrahigh resolution mass spectrometry. SOA was formed in simulation chamber experiments from ozonolysis of a mixture of
four biogenic volatile organic compounds (BVOC): α-pinene, β-pinene, ∆3
10 -carene and
isoprene. The SOA was subsequently aged under three different sets of conditions: in
the dark in the presence of residual ozone, with UV irradiation and OH radicals, and
using UV light only. Among all studied conditions, only OH radical-initiated ageing was
found to influence the molecular composition of the aerosol and showed an increase
15 in carbon oxidation state (OSC) and elemental O/C ratios of the SOA components.
None of the ageing processes produced an observable effect on the oligomers formed
from ozonolysis of the BVOC mixture, which were found to be equally abundant in both
“fresh” and “aged” SOA. Additional experiments using α-pinene as the sole precursor
demonstrated that oligomers are an important group of compounds in SOA produced
20 from both ozonolysis and OH radical-initiated oxidation processes; however, a completely different set of oligomers is formed under these two oxidation regimes. SOA
from the OH radical-initiated α-pinene oxidation had a significantly higher overall OSC
and O/C compared to that from pure ozonolysis experiments confirming that the OH
radical reaction is more likely to be responsible for the occurrence of highly oxidised
25 species in ambient biogenic SOA.
Original languageEnglish
PublisherCopernicus Publications
Pages5359-5389
Number of pages31
DOIs
Publication statusPublished - 25 Feb 2015
Externally publishedYes

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