Characterising seasonal variations and spatial distribution of ambient PM10 and PM2.5 concentrations based on long-term Swiss monitoring data

Collocated parallel measurements of PM2.5 and PM10 were conducted at 7 sites in Switzerland since January 1998, constituting now one of the longest comparative data sets for PM2.5 and PM10 in Europe. The range of the long-term mean concentrations of PM2.5 was between 7.9 μg/m3 at Chaumont and 24.4 μg/m3 in Lugano. For the sites within the Swiss plateau this range narrows from 15.1 μg/m3 at the rural site of Payerne to 20.8 μg/m3 at the directly traffic exposed site of Bern. The long-term averages of the PM2.5/PM10 ratios of the daily values vary only from 0.75 to 0.76, with the exception of the traffic exposed site of Bern (0.59). The correlation between the daily values of PM2.5 and PM10 at all sites is generally high. For PM10, as well as for PM2.5 the highest concentrations are normally observed during wintertime. An exception is Chaumont (1140-m a.s.l.), which is often positioned above the inversion layer during wintertime and, therefore, has the lowest concentration during wintertime. A minimum of the PM2.5/PM10 ratio is often found during spring, probably due to the influence of relatively coarse biogenic particles. Though the sites have quite different exposition characteristics, the correlation of the daily values of PM2.5 and PM10 between the different sites of the Swiss plateau is very high, indicating a dominant influence of regional meteorology over local events and sources. The findings imply that from the point of view of an efficient use of financial and personal resources, the number of collocated PM2.5 measurements at PM10 sites in a monitoring network can be kept quite limited. The saved resources could rather be used to investigate other particle related parameters providing substantial new information (e.g. on particle sources, formation and effects) like PM1, particle number concentrations, morphology or chemical composition.