The pulmonary effects of outdoor ozone and particle air pollution

Over the past three decades, considerable progress has been made in control ling levels of several outdoor air pollutants with well-established effects on human health (e.g., sulfur dioxide, carbon monoxide, and lead). However , concern remains about the potential human health impacts of two air pollu tants, ozone (O-3) and fine particulate matter (PM2.5), for which much less progress has been made. Both O-3 and PM2.5, derive largely from fossil fue l combustion, and both have been shown to have human health effects at leve ls frequently observed in outdoor air. In the case of O-3, controlled chamb er experiments have shown that brief, ambient-level exposures cause acute, reversible drops in lung volumes, increases in nonspecific bronchial respon siveness, and pulmonary inflammation. Epidemiology studies have confirmed m any of these findings and further have demonstrated associations with asthm a exacerbations, emergency room visits, hospital admissions, and deaths. Po pulations most at risk include children and adults who are active outdoors, especially those with asthma, PM2.5 is a heterogeneous mixture of suspende d solid and liquid particles with widely varying diameters and compositions . The evidence for health effects of PM2.5 derives largely from epidemiolog ical studies that have reported associations with both acute and chronic mo rtality in urban areas. Other effects associated with ambient particulate m atter include increases in hospitalizations and respiratory symptoms and de creases in lung function, Populations at greatest risk of PM2.5 effects inc lude the elderly and those with preexisting cardiopulmonary disease. Import ant questions remain regarding PM health effects, including the nature of t he PM component(s) responsible, the biological mechanism(s) involved, and t he host factors that promote greater susceptibility; these are currently ar eas of active research.