[Characteristics of indoor gaseous air pollutants in winter]

There are many gaseous air pollutants found in indoor air. It is very important to precisely measure the concentration of these compounds in order to evaluate the risk to human health and to reduce their concentrations. A diffusive sampling device is suitable for measurement of indoor air, because these are small, light, and can be used without a power supply for the pump. In this study, representative gaseous air pollutants in winter indoor and outdoor air were measured using diffusive sampling devices. Furthermore, the relationship between gaseous air pollutants, secondary formation mechanism, and the outbreak source were examined. The indoor concentrations of aldehydes, nitrogen dioxide and ammonia were higher than outdoor concentrations. By contrast, indoor concentrations of ozone were lower than outdoor concentrations. The indoor concentrations of nitrogen dioxide in 43% houses exceeded the maximum limit stated by environmental law (60 ppb). It was suggested that the main emission sources of nitrogen dioxide are kerosene and gas stoves. In addition, it was suggested that carbonyl compounds are formed by interactions between volatile organic compounds (VOCs) and ozone from outdoor air. Formic acid was estimated to be formed by the oxidation of formaldehyde with ozone, because a positive correlation between formaldehyde and formic acid, and an inverse correlation between formaldehyde and ozone, were observed in indoor air.