Modeling of fine and ultrafine particulate matter in Poland using WRF-Chem

Air pollution caused by particulate matter (PM) remains one of the major environmental challenges in Europe, with fine and ultrafine particles (UFP) posing a particularly serious risk to human health and the climate system. Owing to their small size, UFP can penetrate deep into the respiratory tract and enter the bloodstream, thereby contributing to cardiovascular and pulmonary diseases. In addition, ultrafine aerosols play an important role in atmospheric chemistry and radiative processes. In Central and Eastern Europe, wintertime residential heating based on coal, peat, and wood combustion is a dominant source of elevated PM concentrations and is frequently associated with severe air pollution episodes.While PM2.5 and PM10 have been extensively studied, much less attention has been paid to ultrafine particles. In particular, their spatial variability, their contribution to total particulate matter, and their representation in chemistry–transport models remain insufficiently constrained, especially during the winter heating season. As a result, model evaluation beyond standard mass-based PM metrics is still limited.In this study the WRF-Chem model is used to simulate fine and ultrafine particle pollution over Poland for the period from 10 December 2024 to 3 January 2025, during which several high PM2.5 concentration events linked to residential heating emissions were observed. The simulations employ the MOZART–MOSAIC chemistry and aerosol scheme, which allows for an explicit representation of aerosol size distributions and microphysical processes relevant for combustion-related particles.Model output is evaluated using ground-based observations from the ACTRIS research infrastructure, including size-resolved aerosol measurements, as well as routine PM2.5 observations from the Polish national air quality monitoring network (GIOŚ). The evaluation is based on spatial and temporal collocation of modeled and observed data and focuses on model performance during the winter pollution episode.The results provide insight into the ability of WRF-Chem to reproduce wintertime PM2.5 episodes driven by residential heating emissions and into the role of ultrafine particles in shaping total PM concentrations.This work was supported by the European Union’s programme “Support to Advanced Learning and Training (EU4Belarus- SALTII)”.