Influence of natural hydrocarbons on ozone formation in an isolated power plant plume

On 4 days during the 1995 Southern Oxidant Study (SOS), air samples were ta ken in the plume of the Cumberland Power Plant in Tennessee using an instru mented helicopter. On these days a notable difference ill excess ozone in t he plumes was observed. Excess ozone varied from 20 ppb on July 7, 1995, up , to 55 ppb on July 16. While the total amount of non-methane VOC was quite similar, significant differences were observed in the levels of reactive h ydrocarbons, mostly isoprene. This study examines the parameters that gover n both emission rates of isoprene and its dispersion. These include tempera ture and wind speed on the surface and aloft, total solar radiation, and th e height of the mixed layer. The results revealed and computer model simula tions confirmed that although differences were not very large, the combinat ions of all of these parameters favored lower ambient isoprene levels and, consequently, lower ozone production on July 7 and higher production on the 3 other days.