A New Method for Measuring Average 24-Hour Nitrogen Dioxide Concentrations in the Atmosphere

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Abstract
A long-term manual sampling procedure for nitrogen dioxide is required to measure compliance with the recently adopted EPA ambient air quality standard for this substance. The method recommended by EPA has proven to be inadequate. This paper discusses a manual procedure involving absorption of NO2 in a triethanolamine solution or a triethanolamine impregnated molecular sieve surface. Absorption efficiencies of over 95% are attained, using either the liquid or solid absorbers. The NO2 (gas) to NO2 (ion) factor was found to be 0.85, evaluated against the Saltzman factor of 0.72. Field data as well as controlled laboratory trials indicate the method is comparable to continuous air monitoring instrumentation, utilizing the modified Saltzman reagent. Nitric oxide in concentrations as high as 0.6 ppm for 24 hr gave no interference. The presence of sulfur dioxide causes slightly lower results with the solid absorber, but has no effect on the liquid absorber at concentrations normally encountered in ambient air. This new absorbing reagent can be used for short duration sampling, as well as extended sampling times for up to 4 days.

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