Abstract
The behaviour of nitrogen dioxide (NO2) in humid air within a charcoal sampling medium is described. Dynamic test atmospheres of controlled NO2 concentration, flow and relative humidity were generated from a cylinder containing a reference standard of NO2. These atmospheres were passed through an adsorbent charcoal bed and the elution behaviours of NO2 and nitric oxide (NO) were investigated. The capacity for NO2 was found to be independent of concentration over the range studied (3–42 vpm at 294 K ambient pressure). NO2 was observed to break through the adsorbent rapidly but only at trace levels. No further significant increase in NO2 concentration was noted. However, NO was observed to elute from the adsorbent bed, eventually attaining an eluting concentration equivalent to the NO2 challenge concentration. This conversion process was found to be strongly dependent on the relative humidity of the test atmosphere, and at low relative humidities (<0.1% RH at 294 K and ambient pressure), the NO2 to NO conversion process was strongly inhibited. This behaviour was evaluated in terms of the gas-phase and aqueous chemistry of NOx. Further, the potential for interference effects on trace volatile organic compound determinations using a charcoal sampling medium, with recovery by thermal desorption, arising from NO2 within the sample is highlighted.
Published Version
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