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: 01-01-1982
• ISSN: 0013-936X

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 as much as a factor of 2 at altitudes of 6 km. Discussed are recent modifications to a chemiluminescent (ethylene) ozone detector which permit the instrument to compensate automatically 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% for a 100-torr instantaneous pressure change, and flow rates are returned to the desired set points within 10 sec 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% 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 ( identical with 20,000 ft) and an ozone concentration range of similar to 20-700 p.p.b.