Elemental composition and oxidative properties of PM2.5 in Estonia in relation to origin of air masses — results from the ECRHS II in Tartu

Fine particulate matter (PM2.5) was sampled at an urban background site in Tartu, Estonia over one-year period during the ECRHS II study. The elemental composition of 71 PM2.5 samples was analyzed for different chemical elements using energy-dispersive X-ray fluorescence spectrometry (ED-XRF). The oxidative activity of 36 samples was assessed by measuring their ability to generate hydroxyl radicals in the presence of hydrogen peroxide.The origin of air masses was determined by computing 96-hour back trajectories of air masses with the HYSPLIT Model. The trajectories of air masses were divided into four sectors according to geographical patterns: “Russia,” “Eastern Europe,” “Western Europe,” and “Scandinavia.”During the study period, approximately 30% of air masses originated from “Scandinavia.” The other three sectors had slightly lower values (between 18 and 22%). In spring, summer, and winter, higher total PM levels originated from air masses from continental areas, namely “Russia” and “Eastern Europe” (18.51 ± 7.33 and 19.96 ± 9.23 µg m− 3, respectively). In autumn, the PM levels were highest in “Western Europe”. High levels of Fe, Ti, and AlCaSi (Al, Ca, and Si) were also detected in air masses from the Eurasian continent. The oxidative properties were correlated to the origin of air masses. The ⋅OH values were approximately 1.5 times higher when air masses originated from the direction of “Eastern Europe” or “Russia.”The origin of measured particles was evaluated using principal component factor analysis. When comparing the PM2.5 elemental composition with seasonal variation, factor scores, and other studies, the factors represent: (1) combustion of biomass; (2) crustal dust; (3) traffic; and (4) power plants and industrial processes associated with oil burning.The total PM2.5 is driven mainly by biomass and industrial combustion (63%) and other unidentified sources (23%). Other sources of PM, such as crustal dust and traffic, contribute a total of 13%.