Characterization of atmospheric PM_2.5 sources at a Central European urban background site

For the purposes of this work, a first in Poland, full-year collection of daily PM_2.5 (particulate matter with aerodynamic diameter smaller than 2.5 μm) samples was chemically analyzed to determine the contents of elemental and organic carbon, water-soluble inorganic ions and 21 minor and trace elements in PM in an urban background site in Warsaw. Annual mean PM_2.5 concentration reached 18.8 μg/m³, with the lowest levels in summer (11.5 μg/m³ on average) and the highest in winter (27.5 μg/m³), with several episodes reaching over 80 μg/m³. Strong seasonal differences were observed mainly for the contents of nitrate and secondary organic carbon (SOC), while sulphate showed the least variability. Secondary species constituted on average 45% of PM_2.5 mass, suggesting large influence of regional and long-range transport of pollutants. Source apportionment with the use of positive matrix factorization (PMF) method, supported by the analysis of enrichment factors, led to identification of six main sources of PM_2.5 origin: residential combustion (fresh & aged aerosol) (46% of PM_2.5 mass), traffic exhaust (21%) and non-exhaust (10%) emissions, mineral dust/construction works (12%), high-temperature processes (8%) and steel processing (3%). Including primary organic carbon (POC) and SOC as two separate constituents helped to distinguish between the primary and secondary sources of the aerosol. The identification of sources was also supported by investigating their yearly and weekly profiles, as well as the correlation of PM constituents with meteorological conditions, which are one of the main drivers of heat generation activities. We found that the most distinctive markers of PM sources in Warsaw are SOC, Cl^- and As for residential combustion, NH₄⁺, Sb and POC for road transport, Ca and Mg for construction works and SO₄^2- for long-range transport of PM.