PAN is one of a class of common air pollutants formed by the action of sunlight on volatile organic compounds and nitrogen oxides. No toxicokinetic studies have been found in the available literature. The acute toxicity of PAN is less than that of ozone, similar to NO2 and higher than SO2. The LC30, in mice and rats were 718-743 mg/m3 (for 2 h) and 470 mg/m3 (for 4 h), respectively. Following acute exposure, severe lung lesions and, at the higher levels, damage to the epithelium of upper parts of the respiratory tract were found in animals. It seems that concentrations of 1.19-1.49 mg/m3 lie not far from the threshold required for pulmonary function effects in sensitive individuals. However, these PAN concentrations are well above the maximum ambient concentrations usually experienced within the USA and Canada (0.003-0.078 mg/m3). It appears unlikely that present ambient PAN concentrations would affect pulmonary functions responses to ambient ozone. In human, the lowest level causing eye irritations was 0.64 mg/m3 for 2 h. Concentrations of 0.99 and 4.95 mg/m3 were identified as no-observed-effect level (NOEL) and no-observed-adverse-effect level (NOAEL) for pathological and histological changes in the respiratory system (nasal passages) of rats during subchronic exposures to PAN, but were not considered to be relevant to derivation of a RfC for chronic inhalation exposure. PAN is a weak point mutagen or clastogen. The data are not sufficient to evaluate its carcinogenicity. No study was found which could be used for the derivation of a RfC for acute or chronic inhalation exposure to PAN.