ASSESSMENT OF OZONE EXPOSURES IN THE GREATER METROPOLITAN TORONTO AREA

An ozone (O-3) exposure assessment study was conducted in Toronto, Ontario, Canada during the winter and summer of 1992. A new passive O-3 sampler developed by Harvard was used to measure indoor, outdoor, and personal O-3 concentrations. Measurements were taken weekly and daily during the winter and summer, respectively. Indoor samples were collected at a total of 50 homes and workplaces of study participants. Outdoor O-3 concentrations were measured both at home sites using the passive sampler and at 20 ambient monitoring sites with continuous monitors. Personal O-3 measurements were collected from 123 participants, who also completed detailed time-activity diaries. A total of 2,274 O-3 samples were collected. In addition, weekly air exchange rates of homes were measured. This study demonstrates the performance of our O-3 sampler for exposure assessment. The data obtained are further used to examine the relationships between personal, indoor (home and workplace), and outdoor O-3 concentrations, and to investigate outdoor and indoor spatial variations in O-3 concentrations. Based on home outdoor and indoor, workplace, and ambient O-3 concentrations measured at the Ontario Ministry of the Environment (MOE) sites, the traditional microenvironmental model predicts 72% of the variability in measured personal exposures. An alternative personal O-3 exposure model based on outdoor measurements and time-activity information is able to predict the mean personal exposures in a large population, with the highest R(2) value of 0.41.