References

ACP

Atmospheric Chemistry and Physics

ACP

1680-7324

Copernicus GmbH

Göttingen, Germany

10.5194/acp-12-11037-2012

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

Stanier

¹ ² ³ Singh

¹ ² ³ Adamski

⁴ Baek

² ³ Caughey

⁵ Carmichael

¹ ³ Edgerton

⁶ Kenski

⁷ Koerber

⁷ Oleson

⁸ Rohlf

¹ Lee

S. R.

² ¹² Riemer

⁹ Shaw

¹⁰ Sousan

¹ ² ³ Spak

S. N.

³ ¹¹

Department of Chemical and Biochemical Engineering, University of Iowa, Iowa City, IA 52242, USA

IIHR Hydroscience and Engineering, University of Iowa, Iowa City, IA 52242, USA

Center for Global and Regional Environmental Research, University of Iowa, Iowa City, IA 52242, USA

Wisconsin Department of Natural Resources (WDNR), Madison, WI 53707, USA

Illinois State Water Survey, Champaign, IL 61820, USA

US Atmospheric Research & Analysis Inc., Cary, NC 27513, USA

Lake Michigan Air Directors Consortium, Rosemont, IL 60018, USA

Department of Biostatistics, University of Iowa, Iowa City, IA 52242, USA

Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA

Electric Power Research Institute, Palo Alto, CA 94304, USA

University of Iowa Policy Center, Iowa City, IA 52242, USA

now at: Doosan Heavy Industries & Construction Co., LTD, Seoul, Korea

22 11 2012

12 22 11037 11056

This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

This article is available from http://www.atmos-chem-phys.net/12/11037/2012/acp-12-11037-2012.html

The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/11037/2012/acp-12-11037-2012.pdf

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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