Direct measurements of nitrogen oxides and ozone fluxes over grassland |
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| Authors: | Delany A C Fitzjarrald D R Lenschow D H Pearson R Wendel G J Woodrufl B |
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| Institution: | (1) National Center for Atmospheric Research, 80307 Boulder, CO, U.S.A.;(2) Atmospheric Sciences Research Center, State University of New York at Albany, 12205 Albany, NY, U.S.A.;(3) Department of Atmospheric Sciences, Colorado State University, 80523 Fort Collins, CO, U.S.A.;(4) Thermetics Inc., Waltham, MA |
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| Abstract: | Using the eddy correlation method, fluxes of nitric oxide, nitrogen dioxide, ozone, water, and sensible heat were measured at a site 20 km north of Denver, Colorado over mature crested wheat grass, 0.75 m high in late June and early July. During this period the weather was fair with no synoptic disturbances. In the early morning a well-mixed diluted urban pollution plume traversed the site, by late morning aged pollution had mixed downward into the local boundary layer, and by afternoon the air came from a relatively unpolluted area of the high plains. The mean trace gas concentrations reflect this repeated pattern of local air flow. The fluxes of the trace gases were influenced both by the variation of the means and by other factors including temperature and biological activity. Ozone fluxes were found to be always negative and proportional to the mean, with an average deposition velocity for this case of about 0.006 m s-1. For the oxides of nitrogen this simple treatment was not appropriate. Both deposition and emission were observed, generally deposition predominated in the morning and emission in the afternoon with observed variations in the fluxes of NOx=NO+NO2 from –0.3 to +0.2 ppbv m s-1.The National Center for Atmospheric Research is sponsored by the National Science Foundation |
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| Keywords: | Biosphere-atmosphere exchange biogenic emission eddy correlation dry deposition nitrogen oxides fluxes ozone deposition to grassland turbulent exchange |
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