Airborne measurements of isoprene, CO, and anthropogenic hydrocarbons and their implications

Measurements of the mixing ratios of light hydrocarbons (greater than or eq ual to C-6) were made aboard the National Oceanic and Atmospheric Administr ation Lockheed Orion WP-3 aircraft during June and July of 1994 and 1995 du ring a series of flights over the region around Nashville, Tennessee. The m easurements were carried out as part of the Nashville/ Middle Tennessee Stu dy of the Southern Oxidant Study (SOS) whose purpose was to describe the so urces, variation, and distribution of ozone and its precursors in the south eastern United States during the summer season. The spatial (altitude and l atitude) distribution of isoprene and anthropogenic nonmethane hydrocarbons (NMHCs) is described. The isoprene distribution measured within the planet ary boundary layer over the region is compared to the recent inventories. T he correlations between the various anthropogenic hydrocarbons are used to demonstrate the combined influence of OH photochemistry and dilution on the ir concentrations. Finally, the distributions of those NMHCs that were meas ured are compared to those of CO and methane and discussed in terms their i mplications for odd hydrogen photochemistry and our understanding of region al ozone production. In the boundary layer, OH reactions are dominated by i soprene in the southern part of the region explored and by CO and methane i n the northern part. The other measured NMHCs are seen to play only a minor role in ozone production in the nonurban atmosphere.