The ambient air pollutants ozone, nitric oxide, and ethylene have been monitored in the Pasadena area with a bistatic ir laser apparatus. These pollutants were measured with a differential absorption technique using selected wavelengths in the 9.5-microm, 5.2-microm, and 10.5-mum regions, respectively. The transmitted laser radiation was detected using both direct and heterodyne detection techniques. In the direct detection case cube corner retroreflectors provided the return, and the heterodyne detection responded to scattered radiation from various rough surfaces, ranging from 400 m to 1.9 km in distance from the apparatus. Significant departures from ambient background concentration levels were noticed in the region near a local freeway during periods of moderate and heavy traffic.