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| Titel |
Investigation of the sources and processing of organic aerosol over the Central Mexican Plateau from aircraft measurements during MILAGRO |
| VerfasserIn |
P. F. DeCarlo, I. M. Ulbrich, J. Crounse, B. Foy, E. J. Dunlea, A. C. Aiken, D. Knapp, A. J. Weinheimer, T. Campos, P. O. Wennberg, J. L. Jimenez |
| 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 ; 10, no. 12 ; Nr. 10, no. 12 (2010-06-15), S.5257-5280 |
| Datensatznummer |
250008552
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| Publikation (Nr.) |
 copernicus.org/acp-10-5257-2010.pdf |
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| Zusammenfassung |
| Organic aerosol (OA) represents approximately half of the
submicron aerosol in Mexico City and the Central Mexican Plateau. This study
uses the high time resolution measurements performed onboard the NCAR/NSF
C-130 aircraft during the MILAGRO/MIRAGE-Mex field campaign in March 2006 to
investigate the sources and chemical processing of the OA in this region. An
examination of the OA/ΔCO ratio evolution as a function of
photochemical age shows distinct behavior in the presence or absence of
substantial open biomass burning (BB) influence, with the latter being
consistent with other studies in polluted areas. In addition, we present
results from Positive Matrix Factorization (PMF) analysis of 12-s
High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) OA
spectra. Four components were resolved. Three of the components contain
substantial organic oxygen and are termed semivolatile oxygenated OA
(SV-OOA), low-volatility OOA (LV-OOA), and biomass burning OA (BBOA). A
reduced "hydrocarbon-like OA" (HOA) component is also resolved. LV-OOA is
highly oxygenated (atomic O/C~1) and is aged organic aerosol linked to
regional airmasses, with likely contributions from pollution, biomass
burning, and other sources. SV-OOA is strongly correlated with ammonium
nitrate, Ox, and the Mexico City Basin. We interpret SV-OOA as
secondary OA which is nearly all (>90%) anthropogenic in origin. In the
absence of biomass burning it represents the largest fraction of OA over the
Mexico City basin, consistent with other studies in this region. BBOA is
identified as arising from biomass burning sources due to a strong
correlation with HCN, and the elevated contribution of the ion
C2H4O2+ (m/z 60, a marker for levoglucosan and other
primary BB species). WRF-FLEXPART calculated fire impact factors (FIF) show
good correlation with BBOA mass concentrations within the basin, but show
location offsets in the far field due to model transport errors. This
component is small or absent when forest fires are suppressed by
precipitation. Since PMF factors represent organic species grouped by
chemical similarity, additional postprocessing is needed to more directly
apportion OA amounts to sources, which is done here based on correlations to
different tracers. The postprocessed AMS results are similar to those from
an independent source apportionment based on multiple linear regression with
gas-phase tracers. During a flight with very high forest fire intensity near
the basin OA arising from open BB represents ~66% of the OA mass in
the basin and contributes similarly to OA mass in the outflow. Aging and SOA
formation of BB emissions is estimated to add OA mass equivalent to about
~32–42% of the primary BBOA over several hours to a day. |
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