Analysis of one year's OC/EC data at a Prague suburban site with 2-h time resolution

The behaviour of elemental and organic carbon (EC and OC) in the atmospheric aerosol fraction PM2.5 was measured at a Prague urban background site in the Czech Republic. The measurements were performed by a semi-online field OC/EC analyzer with a two-hour resolution that sufficiently showed the diurnal variability of OC/EC. The seasonal, daily and diurnal behaviour of the EC and OC were studied using an analysis of the collected data. The results of a one-year campaign (Sep 2009-Aug 2010) provide various seasonal patterns of the EC and OC concentrations characteristic for a suburban site in Central Europe. Different sources of carbonaceous aerosols during the various seasons were identified. The winter main sources were probably traffic (mainly EC) and residential heating (both EC and OC). On the other hand, the main EC source in summer is traffic, while the major OC source may be secondary organic aerosols. Winter concentrations were significantly higher than in other seasons. The reason is a combination of stronger air pollution sources in conjunction with poor mixing of the boundary layer. Daily changes of the boundary layer influence the diurnal variations of both EC and OC, too. Afternoon OC concentrations were lower than those at night owing to better daytime atmospheric mixing. The EC late night minima were only slightly lower than the afternoon minima despite much higher traffic in the afternoon. Higher EC concentrations were observed during morning rush hours during all the seasons.