Atmos. Chem. Phys. Discuss., 13, 27891-27936, 2013
www.atmos-chem-phys-discuss.net/13/27891/2013/
doi:10.5194/acpd-13-27891-2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
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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.
Observations of reactive nitrogen oxide fluxes by eddy covariance above two mid-latitude North American mixed hardwood forests
J. A. Geddes and J. G. Murphy
Department of Chemistry, University of Toronto, 80 St. George St., Toronto, ON M5S 3H6, Canada

Abstract. Significant knowledge gaps persist in the understanding of forest–atmosphere exchange of reactive nitrogen oxides, partly due to a lack of direct observations. Chemical transport models require representations of dry deposition over a variety of land surface types, and the role of canopy exchange of NOx (= NO + NO2) is highly uncertain. Biosphere–atmosphere exchange of NOx and NOy (= NOx + HNO3 + PANs + RONO2 + pNO3 + ...) was measured by eddy covariance above a mixed hardwood forest in central Ontario (HFWR), and a mixed hardwood forest in northern lower Michigan (PROPHET) during the summers of 2011 and 2012 respectively. NOx and NOy mixing ratios were measured by a custom built two-channel analyzer based on chemiluminescence, with selective NO2 conversion via LED photolysis and NOy conversion via a hot molybdenum converter. Consideration of interferences from water and O3, and random uncertainty of the calculated fluxes are discussed. NOy flux observations were predominantly of deposition at both locations. The magnitude of deposition scaled with NOy mixing ratios, resulting in campaign-average deposition velocities close to 0.6 cm s−1 at both locations. A~period of highly polluted conditions (NOy concentrations up to 18 ppb) showed distinctly different flux characteristics than the rest of the campaign. Integrated daily average NOy flux was 0.14 mg (N) m−2 day−1 and 0.34 mg (N) m−2 day−1 at HFWR and PROPHET respectively. Concurrent wet deposition measurements were used to estimate the contributions of dry deposition to total reactive nitrogen oxide inputs, found to be 22% and 40% at HFWR and PROPHET, respectively.

Citation: Geddes, J. A. and Murphy, J. G.: Observations of reactive nitrogen oxide fluxes by eddy covariance above two mid-latitude North American mixed hardwood forests, Atmos. Chem. Phys. Discuss., 13, 27891-27936, doi:10.5194/acpd-13-27891-2013, 2013.
 
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