Indoor–outdoor relationships of particulate matter and nitrogen oxides under different outdoor meteorological conditions

Respirable suspended particulate matter and nitrogen oxides concentrations were measured inside and outside a student office in an urban location during a 9-month period. Direct reading tapered-element oscillating microbalance (TEOM) instruments and passive sampling techniques were used to provide indoor and outdoor hourly averages of the two pollutants during the sampling period. The variations and correlations of the pollutant concentrations and the indoor–outdoor (IO) ratio against various outdoor meteorological factors, namely temperature, humidity, pressure, wind speed and solar irradiation were studied. Using a data-mining procedure, suitable sets of data were amassed and grouped together to study the effect of these individual weather parameters on the IO ratio. It is found through statistical regression techniques that temperature, humidity and solar irradiation play a vital role in the variation of the IO ratio. In fact, the IO ratio shows convincing tendency of increase with increase of these three weather parameters. On the other hand, both pressure and wind speed seems to have relatively little effect on the IO ratio.