Laboratory evaluation of an airborne ozone instrument that compensates for altitude/sensitivity effects

• Published in: Environmental science & technology Vol. 17; no. 2; pp. 100 - 103
• Main Authors: Gregory, Gerald L, Hudgins, Charles H, Edahl, Robert A
• Format: Journal Article
• Language: English
• Published: Legacy CDMS American Chemical Society 01-02-1983
• Subjects: Aircraft Instrumentation
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es00108a007

One problem encountered in the use of air-quality instrumentation on aircraft is the variation of instrument sensitivity with pressure as the result of altitude changes of the aircraft. Many instruments experience sensitivity changes of as much as a factor of 2 at altitudes of 6 km. Discussed are recent modifications to a chemiluminescent (ethylene) ozone detector that allow the instrument to automatically compensate for pressure/sensitivity effects. The modification provides automated mass flow rate control for both the sample and ethylene gas flows. The flow control systems maintain flow rate to within 15 percent for a 100-torr instantaneous pressure change, and flow rates are returned to the desired set points within 10 s after the pressure change. During simulated altitude changes (300 m/min from mean sea level to 3-km altitude), flow rates were controlled to within 3 percent of the set point. Laboratory data are summarized verifying the operation of the instrument for a pressure range of 760 torr (sea level) to 350 torr (approximately 20,000 ft) and an ozone concentration range from 20 to approximately 700 ppb.