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| Titel |
Secondary organic aerosol formation exceeds primary particulate matter emissions for light-duty gasoline vehicles |
| VerfasserIn |
T. D. Gordon, A. A. Presto, A. A. May, N. T. Nguyen, E. M. Lipsky, N. M. Donahue, A. Gutierrez, M. Zhang, C. Maddox, P. Rieger, S. Chattopadhyay, H. Maldonado, M. M. Maricq, A. L. Robinson |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 9 ; Nr. 14, no. 9 (2014-05-13), S.4661-4678 |
| Datensatznummer |
250118695
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| Publikation (Nr.) |
 copernicus.org/acp-14-4661-2014.pdf |
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| Zusammenfassung |
| The effects of photochemical aging on emissions from 15 light-duty gasoline
vehicles were investigated using a smog chamber to probe the critical link
between the tailpipe and ambient atmosphere. The vehicles were recruited
from the California in-use fleet; they represent a wide range of model years
(1987 to 2011), vehicle types and emission control technologies. Each
vehicle was tested on a chassis dynamometer using the unified cycle. Dilute
emissions were sampled into a portable smog chamber and then photochemically
aged under urban-like conditions. For every vehicle, substantial secondary
organic aerosol (SOA) formation occurred during cold-start tests, with the
emissions from some vehicles generating as much as 6 times the amount of SOA
as primary particulate matter (PM) after 3 h of oxidation inside the
chamber at typical atmospheric oxidant levels (and 5 times the amount of SOA
as primary PM after 5 × 106 molecules cm−3 h of OH exposure).
Therefore, the contribution of light-duty gasoline vehicle exhaust to
ambient PM levels is likely dominated by secondary PM production (SOA and
nitrate). Emissions from hot-start tests formed about a factor of 3–7 less
SOA than cold-start tests. Therefore, catalyst warm-up appears to be an
important factor in controlling SOA precursor emissions. The mass of SOA
generated by photooxidizing exhaust from newer (LEV2) vehicles was a factor
of 3 lower than that formed from exhaust emitted by older (pre-LEV)
vehicles, despite much larger reductions (a factor of 11–15) in nonmethane
organic gas emissions. These data suggest that a complex and nonlinear
relationship exists between organic gas emissions and SOA formation, which
is not surprising since SOA precursors are only one component of the
exhaust. Except for the oldest (pre-LEV) vehicles, the SOA production could
not be fully explained by the measured oxidation of speciated (traditional)
SOA precursors. Over the timescale of these experiments, the mixture of
organic vapors emitted by newer vehicles appears to be more efficient
(higher yielding) in producing SOA than the emissions from older vehicles.
About 30% of the nonmethane organic gas emissions from the newer (LEV1
and LEV2) vehicles could not be speciated, and the majority of the SOA
formed from these vehicles appears to be associated with these unspeciated
organics. By comparing this study with a companion study of diesel trucks,
we conclude that both primary PM emissions and SOA production for light-duty
gasoline vehicles are much greater than for late-model (2007 and later)
on-road heavy-duty diesel trucks. |
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