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| Titel |
Overview of the LADCO winter nitrate study: hourly ammonia, nitric acid and PM2.5 composition at an urban and rural site pair during PM2.5 episodes in the US Great Lakes region |
| VerfasserIn |
C. Stanier, A. Singh, W. Adamski, J. Baek, M. Caughey, G. Carmichael, E. Edgerton, D. Kenski, M. Koerber, J. Oleson, T. Rohlf, S. R. Lee, N. Riemer, S. Shaw, S. Sousan, S. N. Spak |
| 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 ; 12, no. 22 ; Nr. 12, no. 22 (2012-11-22), S.11037-11056 |
| Datensatznummer |
250011614
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| Publikation (Nr.) |
 copernicus.org/acp-12-11037-2012.pdf |
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| Zusammenfassung |
| An overview of the LADCO (Lake Michigan Air Directors Consortium) Winter
Nitrate Study (WNS) is presented. Sampling was conducted at ground level at
an urban-rural pair of sites during January–March 2009 in eastern Wisconsin,
toward the western edge of the US Great Lakes region. Areas surrounding these
sites experience multiday episodes of wintertime PM2.5 pollution
characterized by high fractions of ammonium nitrate in PM, low wind speeds,
and air mass stagnation. Hourly surface monitoring of inorganic gases and
aerosols supplemented long-term 24-h aerosol chemistry monitoring at these
locations. The urban site (Milwaukee, WI) experienced 13 PM2.5 episodes,
defined as periods where the seven-hour moving average PM2.5
concentration exceeded 27 μg m−3 for at least four
consecutive hours. The rural site experienced seven episodes by the same
metric, and all rural episodes coincided with urban episodes. Episodes were
characterized by low pressure systems, shallow/stable boundary layer, light
winds, and increased temperature and relative humidity relative to
climatological mean conditions. They often occurred in the presence of
regional snow cover at temperatures near freezing, when snow melt and
sublimation could generate fog and strengthen the boundary layer inversion.
Substantial contribution to nitrate production from nighttime chemistry of
ozone and NO2 to N2O5 and nitric acid is likely and requires further
investigation. Pollutant-specific urban excess during episode and non-episode
conditions is presented. The largest remaining uncertainties in the
conceptual model of the wintertime episodes are the variability from
episode-to-episode in ammonia emissions, the balance of daytime and nighttime
nitrate production, the relationship between ammonia controls,
NOx controls and ammonium nitrate reductions, and the extent to
which snow and fog are causal (either through meteorological or chemical
processes) rather than just correlated with episodes because of similar
synoptic meteorology. |
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