Influence of meteorological conditions and seasonality on PM1 and organic aerosol sources at a rural background site

Abstract

Organic aerosols (OA) are a main component of PM_2.5 (20–90%), which contains thousands of compounds. Thus, the formation processes and sources of OA remain poorly understood. In this study, the seasonal and diurnal variabilities of submicron PM chemical composition (both inorganic and organic aerosols) and OA sources were characterized by aerosol mass spectrometry (AMS) and an aethalometer at a rural background site in the Czech Republic (National Atmospheric Observatory Košetice – NAOK) from January to October 2019. The effects of meteorological conditions and local, regional, and long-range atmospheric transport influences in Central Europe were also studied. The overall average submicron PM concentration was 9.26 ± 5.88 μg m⁻³. Using positive matrix factorization (PMF) analysis, we identified four OA factors for summer and five for all other seasons. Three factors were associated with primary sources of OA (POA): hydrocarbon-like OA (HOA), biomass-burning OA (BBOA), and OA from coal burning (CCOA, absent in summer), the CCOA factor enabling a better description of the residential heating effect on the background station in Central Europe. Two remaining factors represented oxygenated OA (OOA) sources: less oxidized OOA (LO-OOA) and more oxidized OOA (MO-OOA).Higher pollution episodes of submicron PM and all OA sources were predominantly associated with continental air masses. The effect of dispersion conditions, as assessed by the ventilation index (VI) and not yet been studied at a rural background site, proved to be a critical factor. The extension of the number of primary factors to include CCOA in PMF analysis, together with the reflection of the influence of seasonality, air mass origin and changes in meteorology, especially dispersion conditions, has elucidated the origin and fate of OA in the atmosphere at this type of European background stations.