Determinants of indoor NO2-concentration and the personal exposures of children and their mothers in Japanese homes.

In February and in July 1986 the personal exposures to NO2 of 60 children and their mothers were measured and NO2-concentrations in their homes were measured. In the summer also the NO2-concentration in the kitchen was determined during the time that the mother was in the kitchen. The mothers were asked to keep a diary of the activities of her and her child during that day and of the time that the heating appliances, cooking range, etc. were used. In the winter indoor NO2-concentrations and personal exposures of mother and child were much higher than in the summer. In the winter in many cases the Japanese Ambient Air Quality Standard is exceeded. The elevated levels in the winter can be related to the use of NO2-producing heating appliances especially the gas- or oilstove without a flue. Appliance of a flue still causes the indoor NO2-concentrations to be elevated. The division of a study population into two exposure categories on the basis of presence of a non-vented gasstove is therefore inappropriate. An instantaneous gas fired water heater may also contribute to elevated indoor NO2-concentrations and personal exposures, although the present survey could not provide detailed information about the use of a flue and the location of the geyser. The time that a gasrange is being used may influence the indoor NO2-concentrations, but the results from this survey were not clear. Ventilation in the kitchen reduces the indoor NO2-concentrations, although this seems especially true in case the gas range is being used for a long time. In houses with smokers higher NO2-concentrations were found than in houses with non smokers. In the winter the non-vented gas stove is the most important indoor NO2-source. The present study was not able to demonstrate the effect of outdoor NO2-concentrations on the indoor air concentrations. A longer time span would be necessary. The housestructure, i.e. the construction of the house and the number of rooms influence the indoor NO2-concentrations and personal exposure. In the winter all indoor NO2-concentrations are highly intercorrelated and also highly correlated with the personal exposures of mother and child. Multiple regression models based on either measured or time-weighted NO2-concentrations explain about 85 percent of the variance in the personal exposures of child and mother in the winter. The exposures calculated from the time-weighted NO2-concentrations correlate very well with the measured personal exposures. This was not the case in the summer.(ABSTRACT TRUNCATED AT 400 WORDS)