Estimation of tropospheric ozone production using concentrations of hydrocarbons and NOx, and a comprehensive hydrocarbon reactivity parameter

We have developed a photochemical model for calculating the ozone concentration in a near-stationary air mass in the lower troposphere using data on chemical composition from August 1993, in the Village of Hastings, Ontario. The calculated concentration of ozone as a function of time was in good agreement with experiment for these data sets, except during incursions of air masses of different origin. Consideration of the mechanism of ozone formation allowed the ozone-forming potential of all hydrocarbons to be considered as a group, rather than using empirical values of ozone molecules formed per substrate molecule destroyed for each individual hydrocarbon. Use of the model predictively indicated that changes in NOx concentration and light intensity had much greater impact upon the calculated ozone concentration than changes in relative humidity and hydrocarbon concentrations. The dependence of ozone concentration upon temperature was almost entirely due to thermal decomposition of peroxyacetyl nitrate (PAN), which adds to the reservoir of NO2 on hot days. (C) 1998 Elsevier Science S.A.