AMBIENT AIR BENZENE CONCENTRATIONS IN CANADA (1989-1993) - SEASONAL AND DAY OF WEEK VARIATIONS, TRENDS, AND SOURCE INFLUENCES

Since 1987, the Pollution Measurement Division of the Environmental Pr otection Service, Environment Canada, has operated a field program for measuring benzene in ambient air. With the cooperation of provincial and municipal environmental agencies, samples have been collected at o ver 30 urban and rural monitoring sites across the country. Samples ar e collected in evacuated canisters and analyzed by gas chromatography with a mass-selective detector. Using data from all sites, the composi te average benzene concentration for Canada over the years 1989 to 199 3 was 3.6 mu g/m(3) and the composite median was found to be 2.6 mu g/ m(3). Benzene concentrations are highest at urban sites near major str eets and at sites influenced by industrial sources. For eighteen urban and suburban trend sites (those with no nearby industrial sources), c omposite annual median benzene concentrations decreased by 20% between 1989 and 1993. For the same period, median benzene concentrations dec reased by 33% at four trend sites with nearby industries. At most moni toring sites the parameters for benzene and CO are highly correlated, supporting the inventory estimate that most emissions of benzene are d ue to vehicle exhaust. For sites with nearby industrial sources of ben zene, the industries are estimated to account for 35 to 70% of the ben zene dose experienced at the sites. These site specific contributions are much more significant than the estimated national emissions assign ed to industrial sources.