The Effect of Sample Humidity on the Response Characteristics of SO₂and NO_xAnalyzer Systems: Aircraft Plume Dispersion Studies

Recent Advances In Air Pollution Analysis

“…45 Chemiluminescent analyzers were found to have advantages over coulometric or colorimetric analyzers in terms of response time and required maintenance. The use of polyethylene sample lines is to be avoided, 18 while short teflon® sample lines are free from interference. 18 Calibration of NO/NO, analyzers is not an entirely straightforward matter.…”

“…The use of polyethylene sample lines is to be avoided, 18 while short teflon® sample lines are free from interference. 18 Calibration of NO/NO, analyzers is not an entirely straightforward matter. Cylinders of dilute NO calibration gas are readily available and serve to calibrate the NO mode of a chemiluminescent analyzer.…”

“…One problem inherent in very fast response analysis of SO 2 is that sample lines, even when constructed of teflon®, appear to adsorb SO 2 , especially at higher relative humidities, causing an extended response time. 18 Another method available commercially uses gas phase fluorescence of SO 2 excited by pulsed light of wavelength 214 nm." i2° The technique is very sensitive (0.5 ppb detection limit), but the more sensitive instrument is of rather slow response time, with a 90% rise time of 2 min.…”

A Critical Review

“…Lower humidities caused sampling efficiency to decrease greatly. In another study of the effect of relative humidity on the response of SO2 and NO X analyzer systems, 190 it was found that at 90% R.H. the concentration of SO2 showed a considerable decrease from the corresponding value at 30% R.H. probably due to interaction of SO2 with water vapor on the walls of the sampling line. The NO X analyzer system was much less sensitive to R.H.…”