Temporally resolved UFP measurements and effect of dispersion conditions on particle concentration levels in a residential area affected by wood-smoke pollution from domestic heating during the winter months

Abstract. The monitoring of ultrafine particle concentrations in ambient air is gaining relevance within the revision of the EU Ambient Air Quality Directive. A prominent source of ultrafine particles (UFP) are combustion processes (e.g. within the scope of wood-fired domestic heating) where the particle emission is typically led unfiltered into the environment contributing significantly to local air pollution. In this study, ultrafine particle concentrations were measured in a residential area affected by wood-smoke pollution during the winter months (Nov. 20, 2024–Mar. 30, 2025) using a diffusion charge based UFP-monitor (AQ Guard Smart 2000 from Palas®). The measurements show a diurnal trend, where concentrations are significantly increased (e.g. >10 000 cm-3) above the background level (approx. 5 000 cm-3) during the morning (approx. 08:00 AM) and evening hours (approx. 07:00 PM–10:00 PM), whereby the source is wood-smoke from the surrounding neighbourhood. The dispersion conditions significantly affect the measured concentrations, as only in case of low (or zero) wind speeds, increased UFP concentrations are obtained demonstrating the relevance of local sources (wood-stove operation) on air quality. In the context of “good practice statements” offered by the World Health Organization's Air Quality guidelines, the maximum daily 1-hour mean concentration of 20 000 cm-3 is exceeded on approx. 33.6 % of days during the measurement period. This significant peak exposure on smaller timescales requires monitoring on a high temporal resolution, as longer averaging periods (e.g. daily or annual mean concentrations) do not reflect temporal peak concentrations that can be especially dangerous for high-risk groups. There is no direct link between legally relevant particulate matter (e.g. PM2.5) and ultrafine particle concentrations, as the size distribution of the wood-smoke emission is in the nanometer region and does not significantly contribute to mass-based particulate matter concentrations.