The Effect of Sample Humidity on the Response Characteristics of SO₂ and NO_x Analyzer Systems: Aircraft Plume Dispersion Studies

Abstract

The response characteristics of two SO₂ analyzers and one NO_x analyzer, fitted with two different types of sample line (polyethylene and Teflon), were tested using air mixtures of about 30 and 90% RH. The response of the SO₂ analyzer system was found to depend strongly on the sample relative humidity, probably due to the interaction of SO₂ with water vapor on the walls of the sample lines. That of the NO_x analyzer was much less sensitive to the relative humidity, no humidity effects being detectable when a 1.3 m, 0.3 cm i.d. Teflon sample line was used. The results suggest that, in many aircraft plume dispersion studies, "true" concentration profiles can be obtained from field data using transient response analysis and an NO* analyzer fitted with a reasonably short Teflon sample line.