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| Titel |
Trends in emissions and concentrations of air pollutants in the lower troposphere in the Baltimore/Washington airshed from 1997 to 2011 |
| VerfasserIn |
H. He, J. W. Stehr, J. C. Hains, D. J. Krask, B. G. Doddridge, K. Y. Vinnikov, T. P. Canty, K. M. Hosley, R. J. Salawitch, H. M. Worden, R. R. Dickerson |
| 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 ; 13, no. 15 ; Nr. 13, no. 15 (2013-08-15), S.7859-7874 |
| Datensatznummer |
250085628
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| Publikation (Nr.) |
 copernicus.org/acp-13-7859-2013.pdf |
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| Zusammenfassung |
| Trends in the composition of the lower atmosphere (0–1500 m altitude) and
surface air quality over the Baltimore/Washington area and surrounding states
were investigated for the period from 1997 to 2011. We examined emissions of
ozone precursors from monitors and inventories as well as ambient
ground-level and aircraft measurements to characterize trends in air
pollution. The US EPA Continuous Emissions Monitoring System (CEMS) program
reported substantial decreases in emission of summertime nitrogen oxides
(NOx) from power plants, up to ∼80% in the
mid-Atlantic States. These large reductions in emission of NOx
are reflected in a sharp decrease of ground-level concentrations of
NOx starting around 2003. The decreasing trend of tropospheric
column CO observed by aircraft is ∼0.8 Dobson unit (DU) per year,
corresponding to ∼35 ppbv yr−1 in the lower troposphere (the
surface to 1500 m above ground level). Satellite observations of long-term,
near-surface CO show a ∼40% decrease over western Maryland
between 2000 and 2011; the same magnitude is indicated by aircraft
measurements above these regions upwind of the Baltimore/Washington airshed.
With decreasing emissions of ozone precursors, the ground-level ozone in the
Baltimore/Washington area shows a 0.6 ppbv yr−1 decrease in the past
15 yr. Since photochemical production of ozone is substantially influenced
by ambient temperature, we introduce the climate penalty factor (CPF) into
the trend analysis of long-term aircraft measurements. After compensating for
inter-annual variations in temperature, historical aircraft measurements
indicate that the daily net production of tropospheric ozone over the
Baltimore/Washington area decreased from ∼20 ppbv day−1 in the
late 1990s to ∼7 ppbv day−1 in the early 2010s during ozone
season. A decrease in the long-term column ozone is observed as ∼0.2
DU yr−1 in the lowest 1500 m, corresponding to an improvement of
∼1.3 ppbv yr−1. Our aircraft measurements were conducted on
days when severe ozone pollution was forecasted, and these results represent
the decreasing trend in high ozone events over the past 15 yr. Back
trajectory cluster analysis demonstrates that emissions of air pollutants
from Ohio and Pennsylvania through Maryland influence the column abundances
of downwind ozone in the lower atmosphere. The trends in air pollutants
reveal the success of regulations implemented over the past decades and the
importance of region-wide emission controls in the eastern United States. |
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