Chronic Ozone Exposure Study. John D. Spengler, Halűk Özkaynak, Alison Geyh, Kiyoung Lee, and Jianping Xue, Harvard University, School of Public Health
Between May 1995 and June 1996, 200 children participated in a study of chronic ozone exposure. The children, mostly 7-12 years old, lived in either Upland, California, 55 km east of downtown Los Angeles, or in the Mountain area around Lake Arrowhead, north of San Bernardino. These areas were selected because of historically high ozone levels. During the summer, weekly outdoor average concentrations were 51 ppb in the Mountain area and 40 ppb in Upland. Both areas had about 75 days per year of expected exceedances of the 120 ppb max 1-hr ozone NAAQS, however, the diurnal patterns were different. In Upland, ozone levels follow a typical pattern for the eastern basin with highest levels seen during early to mid afternoon and decreasing to near zero at night. At elevations of 4000-5000+ feet further east, the highest concentrations are experienced later in the afternoon and often remain high well into the evening. Providing further contrast in chronic ozone exposure is the fact that none of the mountain homes have air conditioning, while most of the valley homes in Upland do. Children wore passive diffusion samplers for six consecutive days once every month. Similar samplers were placed inside and outside their homes. Subjects recorded their daily activities noting indoor and outdoor time, location and transportation. Indoor, outdoor, and personal exposures to ozone were higher for the mountain children than those living in the valley. During the ozone months of June-August, children living in the Upland and Mountain communities were exposed to 50% of the ambient integrated concentrations, as measured by personal badges. Presumably because of air conditioning, the valley homes averaged 36% of ambient levels. Inside mountain homes ozone was 50% of outdoor levels. These differences along with differences in reported time spent outdoors led to mountain children having consistently higher chronic ozone exposure. This study provides further evidence on the importance of housing factors, location, and time-activity patterns on chronic ozone exposure.