| 02 Oct 2025
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.
Competing interests: Frederik Weis and Sebastian Kohler are currently employed by Palas GmbH and worked on the development of the AQ Guard Smart 2000 measurement device
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
This manuscript presents the results of UFP measurements taken on a balcony in a residential area near Karlsruhe. A high-resolution data set is available for the winter months of 2024/25. The UFP data is compared with wind data from the same location. The influence of wind speed on the dispersion of UFP is examined in detail, and the observed concentrations are compared with the new WHO recommendations. Source apportionment is performed by comparing the UFP data with the BC concentrations and taking into account the concentration as a function of time. The conclusion is that wood stoves are the main source. This conclusion is likely, but the influence of traffic cannot be completely ruled out. An analysis of the BC filter samples for a wood combustion tracer could be helpful.
Since most ambient air data currently available is for mass (PM10, PM2.5), UFP data is valuable. Nevertheless, the authors could perhaps state more clearly what is really new about their results.
The manuscript is mostly clearly written and easy to read.
Here are a few comments that point out minor errors or will hopefully help the reader:
2.2: A reference with further information on the UFP monitor would be helpful
Line 164: Is the inlet sample actually dried (if so, how) or only heated?
Fig. 2: Wind speed ranges specified for the wind rose: 1.5 m/s-2 km/h Always use m/s or km/h, explain the scale from 0% to 25% shown in the wind rose.
Fig. 3: Instead of simply specifying the concentrations for three colors, a more detailed scale would be helpful. In the second half of December, concentrations tend to be low. Can this be explained (e.g., by higher temperatures, more wind)?
Fig. 4, right: It is surprising that on days when the 1-hour average exceeded 20,000cm-3, the 15-minute average never exceeded 20,000cm-3.
Line 235: “So not only are the major sources likely not active during the lunch hours, pollutant dispersion has positive impacts on the particle concentration level.” How can a distinction be made between low activity and dispersion by wind?
Fig. 5: same comment as for Fig. 3
Fig. 6 and 7: midnight is either 12 PM or 0 AM