Organic aerosol sources in Krakow, Poland, before implementation of a solid fuel residential heating ban.

Krakow is a pollution hot-spot in Europe which is thought to be caused mainly by a high use of coal combustion (power plants, residential heating). Here, we quantify the impact of coal burning on air quality in the city of Krakow before the use of solid fuels for residential heating was banned within the city of Krakow. The particulate matter (PM)was collected on 126 24-hour filter samples (January to September, both PM1 and PM10, i.e., with an aerodynamic diameter smaller than 1 μm and 10 μm, respectively) and analyzed with an aerosol mass spectrometer and the sources of the organic aerosol (OA) quantified. Secondary OA (SOA) likely from residential heating was the main contributor to winter-time OA (78 % in PM1, 57 % in PM10) and was composed of equal parts of fossil and non-fossil emissions. Additionally, fresh solid fuel combustion emissions from residential heating contributed to OA during winter (coal combustion OA (CCOA): 12 %, biomass burning OA (BBOA): 3%). While BBOA contributed substantially towater-solubleOA, COOA was found to be water-insoluble and thus not identified as part of water-soluble OA. Together with the fairly low water-solubility of winter oxygenated OA (WOOA, 29 %), this leads to a low overall water-solubility of organic carbon during winter (35%). In contrast, spring and summer were characterized by more soluble organic carbon (71% in PM1, 55% in PM10) which was dominated by biogenic sources (non-fossil), i.e., fine biogenic secondary oxygenated OA (summer oxygenated OA (SOOA): 35% inPM1) and coarse primary biological OA (PBOA: 54% in PM10). Overall, here we provide information on OA's sources needed to evaluate the success of mentioned efforts to improve air quality in Krakow in future studies.