SEASONAL AND SPATIAL VARIATION OF INDOOR AND OUTDOOR PARTICULATE MASS AND NITROGEN DIOXIDE CONCENTRATION IN EIGHT SWISS AREAS

摘要

Background: This study is part of the Swiss Study on Air Pollution and Lung and Heart Diseases in Adults (SAPALDIA), a nearly 20-year old cohort study spread in eight geographically diverse areas in Switzerland. Innovative outdoor PM10 and NO2 exposure modeling has been conducted in SAPALDIA earlier for PM10 and NO2, however, its relationship with indoor levels has not been assessed. Aims:The overarching aim is to provide estimates of individual long-term home outdoor traffic-related air pollution exposures for all cohort participants. This paper focuses on seasonal and spatial variation of residential outdoor PM10, PM2.5 and NO2 and its correlation with indoor pollutant levels. Methods: Biweekly NO2 measurements are made at 40 outdoor locations in each study area over three different seasons during 2011-2012. Four (of the eight) areas are additionally monitored for indoor and outdoor PM2.5, PM10, and indoor NO2 at 20 locations. NO2 is measured using passive Passam tubes while PMx are measured using Harvard Impactors at a flow rate of 4L/min. Detailed home characteristics and indoor activities are also recorded for each monitored homes. Results: Mean biweekly outdoor NO2, aggregated across all seasons and sites, is highest in Lugano (32.4+14.9 micrg/m3) and lowest in Montana (12.6±8.3 micrg/m3). Across all eight areas, winter levels are highest (range: 15.9-44.7 micrg/m3) and summer lowest (7.2-20.8 micrg/m3). The indoor NO2 levels are about half of the outdoor levels in winter across all areas but similar in summer. Seasonally averaged outdoor PM10 and PM2.5 ranged 9.7-40.5 micrg/m3 and 5.7-36.8 micrg/m3, respectively. Corresponding indoor levels are 8.1-28.1 micrg/m3 and 4.6-22.1micrg/m3, respectively. Computation of area-specific indoor versus outdoor and between pollutant correlations is currently underway. Conclusions: Our results show significant seasonal differences in outdoor PMx and NO2 levels and large spatial differences within and across Switzerland.