Relationships between PAN, PPN and O₃ at urban and rural sites in Ontario

PAN concentrations were determined during the summer of 1989 and the winter of 1990 at three sites in Ontario representing urban (Toronto), suburban downwind (Stouffville) and rural (Dorset) locations. PAN concentrations were found to reach levels of ≈ 4 ppb in Toronto under conditions of stagnant southerly air flow. Observed PAN concentrations were compared with concurrent measurements of PPN and O₃. PPN concentrations were found to be, on average, between 8 and 11% of those of PAN, with slightly higher PPN/PAN ratios found for air masses that were relatively anthropogenic-pollution impacted. For the Dorset site, however, the dependence on air-mass origin was small. The slopes of regressions of ozone vs PAN were found to increase substantially from urban to rural air masses, with typical O₃/PAN ratios for a mid-range ozone concentration of 50 ppb being 50, 110 and 330, for Toronto, Stouffville and Dorset, respectively. Analysis of the data for Toronto and Stouffville under varying meteorological conditions indicates significant potential for oxidant production in the absence of transport of pollutants from other sources.