Distributions of long-term household exposure of different population groups to nitrogen dioxide.

Exposure distributions to nitrogen dioxide in living rooms during the summer and winter were calculated for four groups of Zagreb inhabitants (high school students, university students, employed, and retired persons) using Duan's Cartesianization method. Households were classified into three categories according to fuel used for cooking and heating--electricity (or no gas use), propane-butane, and natural gas. The results showed a seasonally dependent contribution to exposure in households from outdoor sources through ventilation, while type of fuel used for heating and cooking, representing indoor pollution sources, had a predominant influence on exposure levels. Exposure distribution functions could be represented by lognormal, or summation by proportion of lognormal and normal distributions. A comparison of the results and the proposed exposure guideline value suggests that either the guideline value is too large, or a nitrogen dioxide exposure problem exists only in a small percentage of homes and is caused by the high rate of air exchange between the kitchen and living room.