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| Titel |
Novel Approach for Evaluating Secondary Organic Aerosol from Aromatic Hydrocarbons: SOA Yield and Chemical Composition |
| VerfasserIn |
Lijie Li, Ping Tang, Shunsuke Nakao, Li Qi, Mary Kacarab, David Cocker |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250124005
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| Publikation (Nr.) |
 EGU/EGU2016-3363.pdf |
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| Zusammenfassung |
| Aromatic hydrocarbons account for 20%-30% of urban atmospheric VOCs and are
major contributors to anthropogenic secondary organic aerosol (SOA). However,
prediction of SOA from aromatic hydrocarbons as a function of structure, NOx
concentration, and OH radical levels remains elusive. Innovative SOA yield and
chemical composition evaluation approaches are developed here to investigate SOA
formation from aromatic hydrocarbons. SOA yield is redefined in this work by
adjusting the molecular weight of all aromatic precursors to the molecular weight of
benzene (Yield’= Yieldi×(MWi/MWBenzene); i: aromatic hydrocarbon precursor).
Further, SOA elemental ratio is calculated on an aromatic ring basis rather than the
classic mole basis. Unified and unique characteristics in SOA formed from aromatic
hydrocarbons with different alkyl groups (varying in carbon number and location on
aromatic ring) are explored by revisiting fifteen years of UC Riverside/CE-CERT
environmental chamber data on 129 experiments from 17 aromatic precursors at urban
region relevant low NOx conditions (HC:NO 11.1-171 ppbC:ppb). Traditionally,
SOA mass yield of benzene is much greater than that of other aromatic species.
However, when adjusting for molecular weight, a similar yield is found across the 17
different aromatic precursors. More importantly, four oxygens per aromatic ring
are observed in the resulting SOA regardless of the alkyl substitutes attached to
the ring, which majorly affect H/C ratio in SOA. Therefore, resulting SOA bulk
composition from aromatic hydrocarbons can be predicted as C6+nH6+2nO4 (n:
alkyl substitute carbon number). Further, the dominating role of the aromatic ring
carbons is confirmed by studying the chemical composition of SOA formed from the
photooxidation of an aromatic hydrocarbon with a 13C isotopically labeled alkyl
carbon. Overall, this study unveils the similarity in SOA formation from aromatic
hydrocarbons enhancing the understanding of SOA formation from anthropogenic sources. |
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