Ozone formation and transport in southeastern United States: Overview of the SOS Nashville Middle Tennessee Ozone Study

The Southern Oxidants Study (SOS) is a public-private partnership collectively engaged, since 1989, in a coordinated program of policy-relevant research to improve scientific and public understanding of tropospheric ozone pollution. In the summers of 1994 and 1995, SOS implemented the Nashville/Middle Tennessee Ozone Study. This effort, the second SOS urban intensive study, conducted a series of integrated, process-oriented airborne and surface measurement experiments to better understand the chemistry and meteorology associated with the production, transport, and impact of tropospheric ozone. Specific technical objectives addressed (1) the role of biogenic VOC and NO, emissions on local and regional ozone production, (2) the effect of urban-rural exchange/interchange on local and regional ozone production, (3) sub-grid-scale photochemical and meteorological processes? and (4) the provision of a high-quality chemical and meteorological data set to test and improve observation- and emission-based air quality forecast models. Some of the more significant findings of the 1994-1995 studies include the following: (1) Ozone production in Nashville was found to be close to the transition between NOx-sensitive and VOC-sensitive chemistry. (2) Ozone production efficiency (OPE) in power plant plumes, molecules of ozone formed per molecule of NO, emitted, was found to be inversely proportion to NO, emission rate, with the plants having the greatest NOx, emissions exhibiting the lowest OPE. (3) During stagnant conditions, nighttime winds dominated pollutant transport and represent the major mechanism for transporting urban pollutants to rural areas. Ultimately, results provided by this research will allow improved assessment of existing ozone management strategies and provide better scientific tools for the development of future management strategies.