MEASUREMENTS AND ANALYSIS OF PHOTOCHEMICAL OXIDANTS AND TRACE GASES IN THE RURAL TROPOSPHERE OF THE SOUTHEAST UNITED-STATES

Ambient concentrations of photochemical oxidants (O-3, PAN, HNO3, H2O2 ) and various trace species including reactive nitrogen compounds as w ell as total NOy were measured during June and early July 1992 at a ru ral site, SONIA, in the central Piedmont region of North Carolina, as a part of the Southern Oxidants Study. The measurements were made in a n effort to provide a comprehensive understanding of tropospheric phot ochemistry in the rural Southeastern United States. NOy, NO2, and NO s howed diurnal variations with maxima in the morning between 0600 and 0 900 EST. The maximum NOy, NO, and NO2 concentrations reached were 14.5 , 5.4, and 7.8 ppbv, respectively. The mean NOy concentration was foun d to be 2.63 +/- 1.72 ppbv (n = 819) with an average daily maximum of 3.6 ppbv. The mean concentrations of NO and NO2 for the entire period of measurement were found to be 0.18 +/- 0.37 ppbv (n = 794) and 1.31 +/- 0.99 ppbv/(n = 769). H2O2, HNO3, and PAN showed diurnal variation with maxima in the afternoon and minima at night. Mean concentrations were found to be 0.52 +/- 0.36 ppbv (n = 312), 0.67 +/- 0.33 ppbv (n = 250), and 0.41 +/- 0.24 ppbv (n = 578). The NOx/NOy ratio was used as an indicator of the chemical age of airmasses and the ratio showed st rong positive correlations with the photochemical oxidants HNO3 (r = 0 .76), PAN (r = 0.68), and O-3 (r = 0.79) measured at the site. The rel ationship between the accumulation rate of O-3 and the deviation from the photostationary state was examined based on the measured PSS const ant obtained from the values of [O-3], [NO], and [NO2] measured at the site.