LAKE-MICHIGAN OZONE STUDY (LMOS) - MEASUREMENTS FROM AN INSTRUMENTED AIRCRAFT

As part of the Lake Michigan Ozone Study, the NOAA instrumented King Air research aircraft made a series of flights over Lake Michigan during the summers of 1990 and 1991 to characterize the atmospheric conditions prevailing during times when O3 concentrations exceeded the air quality standard. Most of the time, O3 concentrations were within the normal range (40-70 ppbv) for the location and season, but higher concentrations were measured during the afternoon flights at several isolated locations. During three afternoon flights, high O3 concentrations (> 120 ppbv) were observed along portions of the flight path; the highest 1-min average exceeded 160 ppbv. In two flights the highest O3 concentrations were observed in the lower boundary layer over the eastern portion of the flight track; in one case the high concentrations were found over the western side of the lake throughout the boundary layer. The increased O3 was accompanied by moderately increased SO2 and NOx (10-20 ppbv); outside the region of elevated O3, the SO2 and NOx were less than 2-3 ppbv. The elevated ozone concentrations were related to emissions from the urban region located near the southern and southwestern shores of Lake Michigan.