Evaluation of the tungsten oxide denuder tube technique as a method for the measurement of low concentrations of nitric acid in the troposphere |
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| Authors: | J M Roberts R B Norton P D Goldan F C Fehsenfeld |
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| Institution: | (1) Aeronomy Laboratory, National Oceanic and Atmospheric Administration, 80303 Boulder, CO, U.S.A.;(2) Present address: Cooperative Institute for Research in the Environmental Sciences, NOAA, University of Colorado, 80309 Boulder, CO;(3) Present address: Environmental Chemistry Division, Department of Applied Science, Brookhaven National Laboratory, Upton, 11973 Long Island, NY |
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| Abstract: | The applicability of the tungsten oxide denuder tube technique for the measurement of nitric acid in the rural troposphere was investigated. The technique is based on selective chemisorption of HNO3 from the gas stream, thermal desorption, conversion to NO, and analysis by NO–O3 chemiluminescence. Ammonia, which is also collected and desorbed as NH3 and NO, was separated from the HNO3-derived NO by linear temperature-programed thermal desorption. Possible interferences by NO2, HCN, PAN, and n-propyl nitrate (NPN) were tested and found to be significant under conditions found in the lower troposphere. Simultaneous ambient measurements of HNO3 were made with the tungsten oxide denuder tube and nylon filter methods at a rural site in the Colorado mountains (Niwot Ridge, CO). Nitric acid levels measured by the tungsten oxide denuder tube averaged a factor of 3 higher than levels measured by the nylon filter technique. Tests involving the placement of nylon materials in front of the tungsten oxide denuder tube show that there are species, as yet unidentified, present in the atmosphere that interfere with the measurement of HNO3 by the tungsten oxide technique. |
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| Keywords: | Nitric acid tungsten oxide denuder tube nylon filter tropospheric measurement comparison |
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