Airborne Lidar Mapping of Ozone Concentrations During the Lake Michigan Ozone Study

Abstract

An airborne differential absorption lidar (DIAL) was used during the 1991 Lake Michigan Ozone Study (LMOS) to map the vertical distribution of ozone concentrations across Lake Michigan downwind of urban and industrial areas of the south lake region. The DIAL, which was designed as a compact instrument for installation on relatively small-sized twin-engine aircraft typically used on regional air quality studies, is based on an excimer laser and Raman cell to generate multiple-wavelength ultraviolet energy appropriate for remote measurement of tropospheric ozone.

Collected DIAL data are displayed in terms of contour analyses of vertical ozone concentration distributions across Lake Michigan. During times of southwesterly winds, large-scale urban ozone plumes were observed (mostly over the lake and eastern shoreline) that increased in concentration during the day. Small-scale elevated ozone minima, caused by subsidence of clean air aloft and by chemical destruction of ozone by industrial reactive-gas plumes superimposed on the larger-scale urban ozone plume, resulted in very complex vertical ozone distributions that are difficult to observe without use of remote sensing techniques. DIAL-derived ozone concentrations compare favorably with airborne in-situ ozone measurements.