NOy lifetimes and O-3 production efficiencies in urban and power plant plumes: Analysis of field data

In an effort to describe and characterize power plant plumes in the Nashvil le region, emissions from a small power plant (Gallatin) and a large power plant (Paradise) were examined using data obtained on the Department of Ene rgy G-1 airborne sampling platform. Observations made on July 3, 7, 15, 17, and 18, 1995, were compiled, and a kinetic analysis of the chemical evolut ion of the power plant plumes was performed. Analysis of the power plant pl ume data revealed a very active photochemistry, as had been determined prev iously for the urban plume. Ozone production efficiencies (OPE), defined as the number of molecules of O-3 formed per NOx molecule consumed, were foun d to be 3 for Gallatin and 2 for Paradise. Lifetimes for NOx (2.8 and 4.2 h ours) and NOy (7.0 and 7.7 hours) were determined for Gallatin and Paradise , respectively. These NOx and NOy lifetimes imply rapid loss of NOz (NOz is assumed to be primarily HNO3). Lifetimes for NOz are calculated to be 3 an d 2.5 hours for Gallatin and Paradise, respectively. A sensitivity analysis indicates that the Gallatin NOz lifetime could be as long as 5 hours, brin ging it into agreement with the value determined for the Nashville urban pl ume. It is unlikely that the Paradise NOz lifetime is as long as 4 hours. I f NOz loss is attributed to dry deposition, a 3 hour lifetime implies a dep osition velocity greater than 10 cm s(-1), which is much faster than expect ed based on accepted theory. Possible reasons for this discrepancy are disc ussed.