in four major Canadian cities. Identical surveys and methodology were used to collect this data: random sample telephone selection within the identified telephone exchanges, computerassisted telephone interviews, overselection of children and weekends in the 24 -h recall diary and the same interviewers. Very similar response rates were obtained: 63% ( NHAPS ) and 64.5% ( CHAPS ). Results of comparisons by age within major activity and location groups suggest activity and location patterns are very similar ( most differences being less than 1% or 14 min in a 24 -h day ) with the exception of seasonal differences. Canadians spend less time outdoors in winter and less time indoors in summer than their U.S. counterparts. When exposure assessments use time of year or outdoor / indoor exposure gradients, these differences may result in significant differences in exposure assessments. Otherwise, the 24 -h time activity patterns of North Americans are remarkably similar and use of the combined data set for some exposure assessments may be feasible.

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This study evaluated changes in respiratory health associated with daily changes in fine particulate pollution (PM10). Participants included a relatively healthy school-based sample of fourth and fifth grade elementary students, and a sample of patients with asthma 8 to 72 yr of age. Elevated PM10 pollution levels of 150 micrograms/m3 were associated with an approximately 3 to 6% decline in lung function as measured by peak expiratory flow (PEF). Current day and daily lagged associations between PM10 levels and PEF were observed. Elevated levels of PM10 pollution also were associated with increases in reported symptoms of respiratory disease and use of asthma medication. Associations between compromised respiratory health and elevated PM10 pollution were observed even when PM10 levels were well below the 24-h national ambient air quality standard of 150 micrograms/m3. Associations between elevated PM10 levels, reductions in PEF, and increases in symptoms of respiratory disease and asthma medication use remained statistically significant even when the only pollution episode that exceeded the standard was excluded. Concurrent measurements indicated that little or no strong particle acidity was present.

Numerous studies have observed health effects of particulate air pollution. Compared to early studies that focused on severe air pollution episodes, recent studies are more relevant to understanding health effects of pollution at levels common to contemporary cities in the developed world. We review recent epidemiologic studies that evaluated health effects of particulate air pollution and conclude that respirable particulate air pollution is likely an important contributing factor to respiratory disease. Observed health effects include increased respiratory symptoms, decreased lung function, increased hospitalizations and other health care visits for respiratory and cardiovascular disease, increased respiratory morbidity as measured by absenteeism from work or school or other restrictions in activity, and increased cardiopulmonary disease mortality. These health effects are observed at levels common to many U.S. cities including levels below current U.S. National Ambient Air Quality Standards for particulate air pollution. Images Figure 1.

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