The correlation of temperature and rural ozone levels in southeastern U.S.A.

As a part of the southern oxidant study, a comprehensive air quality study was performed at a rural site in southern Tennessee. The observations performed between 25 July and 2 September 1991 included measurements of primary and secondary pollutants as well as meteorological measurements. Relatively high levels of NOy were observed when CO and SO2 levels were at estimated regional background indicating a significant non-combustion source. A multivariate linear regression analysis suggested that nearly of the NOy above the estimated regional background level relates to SO2 emitting sources with the remaining to CO emitting sources. The association between primary pollutants and temperature was found to be weak or insignificant. However, most secondary pollutants (except PAN) positively correlated with temperature. In the case of O3, a better association was found with a combination of temperature and NOy. Comparison between the observation and model simulation suggested that approximately 50% of the increase in O3 levels observed at the Giles site may relate to the intrinsic dependence of rate constants on temperature. The number of O3 molecules produced per NOy molecule present increases with temperature (between 22 and 33°C) as did the chemical air mass age (NOx/NOy). On the other hand, the number of O3 molecules produced per molecule of NOx consumed remained nearly constant. The difference between NOz and the sum of the individual NOz species measured separately (PAN, HNO3 and nitrate aerosol) suggests the presence of an additional NOz species that increased with temperature.