Abstract
Ground level ozone, NO sub(x) , and specific C sub(2) -C sub(6) hydrocarbon measurements from a rural site in NW England during a photochemical pollution episode are presented. Maximum hourly ozone concentrations exceeded 80 p.p.b. for 10 consecutive days with a maximum of 156 p.p.b. Midmorning ozone concentrations were found to be indicative of the amount of ozone from continental sources. The air mass trajectories, total NMHC, and alkane: alkene ratios all indicate that, in the early to middle stages of the episode, the air had been exposed to recent precursor emissions relative to more aged air before and after this period. The measurements are compared with the predictions of recent theoretical models of ozone formation over England.