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No. 338: The Particle Project 2018

Nøjgaard, J. K., Massling, A., Ellermann, T., 2019. The Particle Project 2018. Aarhus University, DCE – Danish Centre for Environment and Energy, 18 pp. Scientific Report from DCE – Danish Centre for Environment and Energy No. 338. http://dce2.au.dk/pub/SR338.pdf

Summary

Time series of atmospheric particles smaller than 2.5 µm (PM2.5) and particles smaller than 10 µm (PM10) measured by TEOM at the rural site RISØ and curbside stations in Aarhus (AARHG) and Copenhagen (HCAB) are presented in The particle Project 2017-2018. Also covered are submicron particle size distributions are furthermore measured at RISØ, in urban background (HCØ), HCAB and at the suburban site (HVID). Finally, Elemental Carbon (EC) has been analysed in ambient PM2.5 at HCØ since September 2014 and compared to RISØ, HCAB and HVID, which was established in October 2015.

Regional and long-range transported aerosols are to a large extent expected to contribute to the particle number concentration in the submicrometer size range. On a relative base the highest contribution of such aerosols are found at rural background sites, e.g. RISØ in Denmark. Long-range transported aerosols also consequently contribute to other sites which are located with smaller distances to local sources.

For Denmark, the relative contribution of long-range transported aerosols therefore decreases when considering the suburban site at HVID, urban back-ground site HCØ and most pronounced at the urban curbside site HCAB, where highest number concentrations are measured due to a strong local traffic source. A trend of decreasing concentrations can be found at all stations when considering time periods of the order of a decade. From 2017 to 2018, particle number concentrations increased at HVID and HCAB, where anthropogenic sources influence the stations. On the other hand, particle numbers decreased in the same period at RISØ and HCØ, which are not directly influenced by local sources. These changes were observed for both ultrafine particles (41 - 110 nm in this study) and particles in the range 110 – 478/550 nm. In 2016 and 2017, higher particle number concentrations have been measured at HVID which is influenced by elevated wood stove emissions during winter-time. In 2018, particle number concentrations at HCØ exceeded those at HVID, which is probably a consequence of the low data coverage at HCØ, variations due to meteorology and within the range of measurement uncertainty.

PM2.5 measurements at HCAB in 2018 using TEOM did not change from its annual concentration in 2017 (10 µg/m3), but has decreased steadily since the onset of the time series in 2002 (17 µg/m3). On the other hand, PM10 at RISØ, AARHG and HCAB decreased 5-8% from 2017 – 2018. Over longer time series, PM10 did not change significantly. At RISØ and HCAB, where common time series have existed since 2011, the concentrations in 2018 are similar to those measured in 2011 (14 and 31 µg/m3, respectively).

EC averaged 0.29 µg/m3 at RISØ and 0.35 µg/m3 at HCØ in 2018. Higher concentrations were measured at the suburban station HVID (0.40 µg/m3) and even higher at HCAB (1.13 µg/m3. Both suburb and urban background were elevated with respect to EC compared to the rural site RISØ, i.e. 22% at HCØ and 39% and HVID in 2018. For the longest time series at RISØ, the annually averaged EC is 0.32 µg/m3 based on 9 years of measurements varying from 0.18 µg/m3 during the 3 summer months and 0.45 averaged over the 3 winter months. EC concentrations have showed an overall decreasing trend at HCAB since 2010, whereas little change has been observed at RISØ, HCØ and HVID.