Health effects associated with ozone and nitrogen dioxide exposure

Of the oxidants and nitrogenous compounds found in ambient air, O sub(3) and NO sub(2) are among those most thoroughly investigated. Large health data bases have been compiled in air quality criteria documents, which serve as the basis for review of primary (health) national ambient air quality standards (NAAQS) for each pollutant. When comparisons can be made, O sub(3) is generally more toxic than other photochemical oxidant species at or near ambient levels, although NO sub(2) does not appear to be of more concern with respect to carcinogenesis. Public health effects of concern for O sub(3) range from acute symptoms (e.g. cough) and decreased lung function to persistent functional changes and permanent scarring of lung tissue, a possible precursor to chronic lung disease. Impairment of immune defenses and increased susceptibility to lung infection have also been associated with O sub(3) exposure. Populations at greatest risk include exercising healthy persons, children, and those with preexisting lung disease. Nitrogen dioxide exhibits similar health effects but at higher concentrations. Health effects data for O sub(3) and NO sub(2) are under consideration in the current review of both primary NAAQS.