Ammonia measurements at Niwot Ridge,Colorado and point arena,California using the tungsten oxide denuder tube technique |
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| Authors: | James M Roberts Andrew O Langford Paul D Goldan Fred C Fehsenfeld |
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| Institution: | (1) Aeronomy Laboratory, NOAA Environmental Research Laboratories, 80303 Boulder, CO, U.S.A.;(2) Present address: Environmental Chemistry Division, Department of Applied Science, Brookhaven National Laboratory, Upton, 11973 Long Island, NY, U.S.A.;(3) Cooperative Institute for Research in the Environmental Sciences, University of Colorado, 80309 Boulder, CO, U.S.A. |
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| Abstract: | The applicability of the tungsten oxide denuder tube technique for the measurement of ammonia in the rural troposphere was investigated. The technique is based on selective chemisorption of NH3 from a gas stream, thermal desorption, conversion to NO, and analysis by NO–O3 chemiluminescence. Nitric acid, which is also collected and desorbed as NO, was distinguished from NH3 by differences in desorption temperature. Substituted amines were also collected, but desorbed at a slightly lower temperature than NH3 in dry air. At high relative humidities, alkylamines may be hydrolyzed to NH3 on the denuder surface and hence detected as NH3. Overheating of the denuder tube during the temperature-programmed desorption was found to cause significant irreversible degradation of system performance.The technique was used to measure NH3 mixing ratios at two rural locations in the United States. At a mountain site in Colorado during the winter of 1984, the average NH3 mixing ratio was 0.20 ppbv ( =0.08 ppbv). At an isolated coastal site in northern California during the spring of 1985, the average NH3 mixing ratio was 0.36 ppbv (=0.17 ppbv). Correlations of the latter measurements with wind direction and NO
x
level suggest that the NH3 mixing ratio in Pacific marine air at 40°N is <-0.25 ppbv. |
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| Keywords: | Ammonia tungsten oxide tungstic acid tropospheric measurement |
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