Spatial and temporal variability of ultrafine particles, NO2, PM2.5, PM2.5 absorbance, PM10 and PMcoarse in Swiss study areas

highlights � We measured NO2 ,P M2.5 ,P M2.5 absorbance, PM10 and UFP in Switzerland using standard methodology. � We studied spatial and seasonal contrasts of these pollutants and PMcoarse across study areas. � PNC and LDSA were highly correlated with each other and with NO2 and PM2.5 absorbance. � More spatial variance occurred within than between study areas for NO2 and PMcoarse, but not for other pollutants. � The air quality standard for PM2.5 proposed by WHO was exceeded at over 90% of measurement sites. abstract Exposure to outdoor air pollutants remains an important concern in Europe, as limit values for NO2 and PM10 continue to be exceeded. Few studies have addressed the long-term spatial contrasts in PM2.5 ,P M absorbance, PMcoarse and especially ultrafine particles. This scarcity of data hampers the possibility to conduct epidemiological studies, assessing the health relevance of these markers of potentially harmful pollutants. Air pollution measurements were performed in eight geographically distinct areas of the Swiss Study on Air Pollution and Lung and Heart Diseases in Adults (SAPALDIA) in Switzerland. NO2 was measured in all eight areas at 40 sites per area, and PM2.5 ,P M2.5 absorbance, PM10 and ultrafine particles (particle number concentration (PNC) and lung deposited surface area (LDSA)) were measured in 4 of these areas, at a subset of 20 out of 40 sites. Each site was sampled three times during different seasons of the year, using the same equipment, sampling protocols and the same central facilities for analysis of samples. We assessed the spatial variability between areas and between individual sites, as well as pollution contrasts between the seasons and correlations between different pollutants. Within-area spatial contrasts (defined as the ratio between the 90 th and 10th percentile) were highest for NO2 (3.14), moderate for PMcoarse (2.19), PNC (2.00) and PM2.5 absorbance (1.94), and lowest for LDSA (1.63), PM2.5 (1.50) and PM10 (1.46). Concentrations in the larger cities were generally higher than in smaller towns and rural and alpine areas, and were higher in the winter than in the summer and