26.
SOA (Secondary Organic Aerosol) Formation in the Presence of
Diesel Soot Exhaust
Sangdon
Lee, Myoseon Jang, Richard M. Kamens
Environmental
Sciences and Engineering, University of North Carolina, Chapel
Hill, NC
Organic aerosol material that forms in the atmosphere
as a consequence of atmospheric reactions, are often called secondary
organic aerosols (SOAs). These aerosols have the potential to
influence climate change by altering the earth’s radiative
balance and by acting as cloud condensation nuclei. They may also
have adverse health effects associated with respiratory and circulatory
diseases. These atmospheric secondary organic aerosols (SOAs)
can be produced by the gas phase oxidation of a class of compounds
called terpenes (e.g. ?-pinene, ?-pinene, d-limonene, etc.) that
come from biogenic sources, and aromatics (e.g. toluene) that
come from anthropogenic sources.
SOA formation usually occurs in the presence of
preexisting particles because they are ubiquitous in the atmosphere.
?-pinene was chosen in this study because it is one of the most
abundant monoterpenes and its atmospheric oxidative reactions
are well-known. Freshly emitted diesel soot particles were selected
as preexisting seed particles, because these particles are mostly
composed of long-chain alkanes and alkanoic acids, which have
very different polarities from oxygenated SOA products. Atmospheric
experiments were carried out in a large outdoor Teflon film smog
chamber. Results from this work show some of the possible impacts
of the preexisting particulate matter on SOA formation from the
?-pinene-NOx photo-oxidative reaction system. First, dilute diesel
exhaust photo-oxidation by itself generates significant amounts
of SOA. This has not been previously reported or quantified. Second,
?-pinene SOA results in a dramatic alteration of the diesel particle
chemical composition, as the air mass ages in the chamber. These
observations suggest that the composition of urban combustion
related particulate matter, due to atmospheric chemical reactions,
may be dramatically different from that based just on the estimates
of source related emissions.
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