Assessment of air pollution origin based on year-long parallel measurement of PM and PM at two suburban sites in Prague, Czech Republic.

From 2nd April 2008 to 28th March 2009, a total 248 daily samples of the PM and PM were collected every sixth day parallel at two suburban sites (Libuš and Suchdol) located at the two opposite sides (south and north, respectively) of Prague, Czech Republic. The PM samples were analyzed for ions by ion chromatography (IC), organic and elemental carbon (OC and EC) by OC/EC analyzer and PM samples also for 56 elements by inductively coupled plasma-mass spectrometry (ICP-MS). The average annual PM and PM was 24.4 ± 13.0 μg m and 26.7 ± 15.1 μg m, respectively, in Prague-Libuš, and 25.1 ± 22.1 μg m and 27.1 ± 23.2 μg m, respectively, in Prague-Suchdol. Since the species forming large part of the aerosol mass were strongly correlated (Spearman's rank correlation coefficient r > 0.80), the variability of PM and PM concentration was mainly driven by the local meteorology or regional and/or long range transport. PM mass closure was calculated based on analytical results with the average percentage of recalculated mass of 77 ± 19% in Prague-Libuš and 86 ± 16% in Prague-Suchdol. The most abundant groups in PM at both sites during the four seasons were OM (Prague-Libuš 34% and Prague-Suchdol 37%) and SIA (Prague-Libuš 30% and Prague-Suchdol 34%). The Positive Matrix Factorization (PMF) was applied to the chemical composition of PM from both sites (124 samples) together to determine its sources. The nine factors were assigned as: mixed factor secondary sulphate and biomass burning, secondary sulphate, traffic, secondary nitrate, road dust, residential heating, aged sea salt, industry and mixed factor road salt along with aged sea salt. According to the polar plots and ventilation index (VI) east/west classification analysis the sources were separated based on origin to four categories local, urban agglomeration, regional and long range transport (LRT). The mixed source secondary sulphate and biomass burning, residential heating and industry were common sources of local origin at both sites. Prague-Suchdol was influenced by traffic related pollution from the urban agglomeration more than Prague-Libuš where the traffic and road dust/salt were of local origin. The regional pollution by secondary sulphates and nitrate was also relevant at both sites along with long range transport of sea salt from North Atlantic Ocean, Norwegian Sea and North Sea. The contribution of the local sources to PM was significant mainly at Prague-Libuš site. However, the sources of regional origin were also important and influence of urban agglomeration pollution to PM is not negligible as well.