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| Titel |
Sources, seasonality, and trends of southeast US aerosol: an integrated analysis of surface, aircraft, and satellite observations with the GEOS-Chem chemical transport model |
| VerfasserIn |
P. S. Kim, D. J. Jacob, J. A. Fisher, K. Travis, K. Yu, L. Zhu, R. M. Yantosca, M. P. Sulprizio, J. L. Jimenez, P. Campuzano-Jost, K. D. Froyd, J. Liao, J. W. Hair, M. A. Fenn, C. F. Butler, N. L. Wagner, T. D. Gordon, A. Welti, P. O. Wennberg, J. D. Crounse, J. M. Clair, A. P. Teng, D. B. Millet, J. P. Schwarz, M. Z. Markovic, A. E. Perring |
| 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 ; 15, no. 18 ; Nr. 15, no. 18 (2015-09-23), S.10411-10433 |
| Datensatznummer |
250120044
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| Publikation (Nr.) |
 copernicus.org/acp-15-10411-2015.pdf |
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| Zusammenfassung |
| We use an ensemble of surface (EPA CSN, IMPROVE, SEARCH, AERONET), aircraft
(SEAC4RS), and satellite (MODIS, MISR) observations over the southeast
US during the summer–fall of 2013 to better understand aerosol sources in the
region and the relationship between surface particulate matter (PM) and
aerosol optical depth (AOD). The GEOS-Chem global chemical transport model
(CTM) with 25 × 25 km2 resolution over North America is used
as a common platform to interpret measurements of different aerosol variables
made at different times and locations. Sulfate and organic aerosol (OA) are
the main contributors to surface PM2.5 (mass concentration of PM finer
than 2.5 μm aerodynamic diameter) and AOD over the southeast US. OA
is simulated successfully with a simple parameterization, assuming
irreversible uptake of low-volatility products of hydrocarbon oxidation.
Biogenic isoprene and monoterpenes account for 60 % of OA, anthropogenic
sources for 30 %, and open fires for 10 %. 60 % of total aerosol
mass is in the mixed layer below 1.5 km, 25 % in the cloud convective
layer at 1.5–3 km, and 15 % in the free troposphere above 3 km. This
vertical profile is well captured by GEOS-Chem, arguing against a
high-altitude source of OA. The extent of sulfate neutralization
(f = [NH4+]/(2[SO42−] + [NO3−]) is only
0.5–0.7 mol mol−1 in the observations, despite an excess of ammonia
present, which could reflect suppression of ammonia uptake by OA. This would
explain the long-term decline of ammonium aerosol in the southeast US,
paralleling that of sulfate. The vertical profile of aerosol extinction over
the southeast US follows closely that of aerosol mass. GEOS-Chem reproduces
observed total column aerosol mass over the southeast US within 6 %,
column aerosol extinction within 16 %, and space-based AOD within
8–28 % (consistently biased low). The large AOD decline observed from
summer to winter is driven by sharp declines in both sulfate and OA from
August to October. These declines are due to shutdowns in both biogenic
emissions and UV-driven photochemistry. Surface PM2.5 shows far less
summer-to-winter decrease than AOD and we attribute this in part to the
offsetting effect of weaker boundary layer ventilation. The SEAC4RS aircraft
data demonstrate that AODs measured from space are consistent with surface
PM2.5. This implies that satellites can be used reliably to infer
surface PM2.5 over monthly timescales if a good CTM representation of
the aerosol vertical profile is available. |
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