SPATIOTEMPORAL VARIATION OF PARTICLE NUMBER AND SURFACE AREA CONCENTRATION IN FOUR SWISS AREAS AND ITS RELATIONSHIP WITH MASS MEASUREMENTS

Abstract

Background: This study is part of the Swiss Study on Air Pollution and Lung and Heart Diseases in Adults (SAPALDIA), a cohort study initiated in 1990 and spread across eight geographically diverse areas in Switzerland. Innovative exposure modeling has been conducted in SAPALDIA earlier for PM10 and NO2, however, exposure to specific traffic related pollutants such as ultrafine particles and PM constituents has not been assessed. Aims:The overarching aim is to provide the estimates of individual long-term outdoor traffic-related air pollution exposures of the cohort participants. This paper focuses on the spatial and temporal variation of home outdoor particle number (PN) and lung-deposited surface area (LDSA) concentration in four study areas: Basel, Geneva, Lugano and Wald. Methods: Weekly outdoor PN and LDSA are measured at 20 residences each in four study areas in three seasons over a period of 2 years, 2011-2012. PN and LDSA are measured using a portable particle counter, miniDiSC (miniature diffusion size classifier). It is a portable diffusion charging based device and measures nanometer sized (10-300nm) particles with a time-resolution of one second. Results: Mean weekly outdoor PN levels aggregated across all seasons and sites are 11000±3700, 15400±8430 and 15700±7200 particles/cm3 in Basel, Geneva and Lugano, respectively. As expected, PN are highest in winter and lowest in summer for all study areas/sites. PN levels show a clear morning and evening rush hour in all seasons in all sites, but more prominently at street sites. PN shows reasonably moderate correlation with NO2 but poor to no correlation with other PM mass metrics in all seasons. Analysis of LDSA measurements and comparison with PN and other pollutants is currently underway. Conclusions: Our results show significant seasonal and spatial variation in home outdoor PN levels within and between study areas and document the differential impact of traffic on PN levels in all study areas.