Atmos. Chem. Phys. Discuss., 9, 17157-17181, 2009
© Author(s) 2009. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Organic nitrogen in PM2.5 aerosol at a forest site in the Southeast US
M. Lin1, J. Walker2, C. Geron2, and A. Khlystov1
1Department of Civil and Environmental Engineering, Duke University, Box 90287, Durham, NC 27708, USA
2National Risk Management Research Laboratory, US Environmental Protection Agency, Research Triangle Park, NC, 27711, USA

Abstract. There is growing evidence that organo-nitrogen compounds may constitute a significant fraction of the aerosol nitrogen (N) budget. However, very little is known about the abundance and origin of this aerosol fraction. In this study, the concentration of organic nitrogen (ON) and major inorganic ions in PM2.5 aerosol were measured at the Duke Forest Research Facility near Chapel Hill, NC, during January and June of 2007. A novel on-line instrument was used, which is based on the Steam Jet Aerosol Collector (SJAC) coupled to an on-line total carbon/total nitrogen analyzer and two on-line ion chromatographs. The concentration of ON was determined by tracking the difference in concentrations of total nitrogen and of inorganic nitrogen (determined as the sum of N-ammonium and N-nitrate). The time resolution of the instrument was 30 min with a detection limit for major aerosol components of ~0.1 μg m−3.

Nitrogen in organic compounds contributed ~33% on average to the total nitrogen concentration in PM2.5, illustrating the importance of this aerosol component. Absolute concentrations of ON, however, were relatively low (<1.0 μg m−3) with an average of 0.18 μg m−3. The absolute and relative contribution of ON to the total aerosol nitrogen budget was practically the same in January and June. In January, the concentration of ON tended to be higher during the night and early morning, while in June it tended to be higher during the late afternoon and evening. Back-trajectories and correlation with wind direction indicate higher concentrations of ON in continental air than in marine air masses and indicate a variety of potential sources.

Citation: Lin, M., Walker, J., Geron, C., and Khlystov, A.: Organic nitrogen in PM2.5 aerosol at a forest site in the Southeast US, Atmos. Chem. Phys. Discuss., 9, 17157-17181, doi:10.5194/acpd-9-17157-2009, 2009.
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