MEASUREMENTS OF INDOOR AND OUTDOOR NITROGEN-DIOXIDE CONCENTRATIONS USING A DIFFUSIVE SAMPLER

The Willems badge,a short-term diffusion sampler was used to measure n itrogen dioxide concentrations inside and outside the homes of partici pants in the European study 'PEACE' (Pollution Effects on Asthmatic Ch ildren in Europe), The main aim of the study was to determine levels o f nitrogen dioxide concentrations both outside and inside children's h omes, and to estimate the indoor/outdoor ratios for nitrogen dioxide i n an urban area, in comparison with a less urbanized control area. We conducted measurements in 23 homes in Ume (a) over circle, a city of a bout 100000 inhabitants in the northern part of Sweden, in addition to 20 homes in a less urbanized control area situated about 20 km from U me (a) over circle. Measurements were made on two different occasions in each home during the period January-March, 1994, The houses were no t equipped with any gas appliances, The mean outdoor 24-h concentratio n in Ume (a) over circle was 28 mu g m(-3) and the mean indoor concent ration was 11 mu g m(-3). The mean indoor:outdoor ratio was 0.44 (s = 0.23). The highest outdoor value, measured in the city centre of Ume ( a) over circle, was 54 mu g m(-3). In the control area the mean ambien t 24-h concentration was 12 mu g m(-3) approximately half as high as i n the urban area, and the mean indoor concentration was 6 mu g m(-3). The mean indoor:outdoor ratio was 0.67 (s = 0.55). The correlation coe fficient between indoor and outdoor concentrations was higher in the c ontrol area, r = 0.79 (p < 0.001), in comparison with the urban area, r = 0.43 (p < 0.01). It is concluded that the outdoor as well as the i ndoor concentrations of nitrogen dioxide were approximately a twice as high in Ume (a) over circle as in the control area. This could be exp lained by heavier traffic density in Ume (a) over circle. The mean 24- h concentration outside homes in Ume (a) over circle was, however, bel ow the 24-h national standard level of 75 mu g m(-3), The higher corre lation between indoor and outdoor concentrations, combined with higher indoor:outdoor ratio, in the control area is interpreted as a sign of a lower level of penetration of outdoor air into the houses in the ur ban area, This was not explained by differences in types of buildings between the two areas, but possibly by differences in air-exchange rat es and in habits of ventilating rooms with open windows.