SEASONAL AND YEARLY PATTERNS OF INDOOR NITROGEN-DIOXIDE LEVELS - DATAFROM ALBUQUERQUE, NEW-MEXICO

There are few data sets appropriate for characterizing the indoor conc entrations of air pollutants over the long tem. An understanding of th e variability in indoor pollutant levels is particularly relevant to t he design of epidemiologic investigations: misclassification of exposu re due to the inaccuracy of exposure estimates tends to weaken the ass ociation of exposure with health outcome. This paper uses a series of indoor NO2 measurements collected at two-week intervals over 18-month periods be 1988 and 1991 to describe the seasonal and year-to-year var iability in indoor NO2. The data show that there can be large year-to- year differences in both the sample distribution of indoor NO2 as well as the household average. For homes with gas ranges with continuously -burning pilot lights, the average bedroom NO2 concentration was 25% h igher in the winter of 1990-1991 than in the winter of 1989-1990 but o nly 4% higher during the winter of 1988-1989 than during the winter of 1989-1990. The winter-to-winter correlations within homes ranged from a low of 0.53 to a high of 0.88. The year-to-year differences in mean indoor concentrations were wt related to temperature. Occupant behavi ors that influence air exchange rate and/or source use are hypothesize d to be the major determinant of the observed pattern. Exposure data c ollected during a single year should be cautiously extrapolated to oth er years. However, in Albuquerque homes, the data suggest that the yea r-to-year variability in household NO2 levels will not have a strong i mpact on classifying exposure into broad categories.