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No. 385: The Particle Project 2019

Nøjgaard, J. K., Massling, A., Ellermann, T., 2020. The Particle Project 2019. Aarhus University, DCE – Danish Centre for Environment and Energy, 22 pp. Scientific Report from DCE – Danish Centre for Environment and Energy No. 385. http://dce2.au.dk/pub/SR385.pdf  

Summary

The Particle Project 2019 reports series of particle size distributions and Elemental Carbon (EC) in fine particles with diameter smaller than 2.5 µm (PM2.5) in urban background. These measurements are carried out as a supplement to the Danish air quality monitoring program under NOVANA. Trends in Urban background (HCØ) are compared to rural location (RISØ), suburban location (HVID) and urban curbside (HCAB). Furthermore, trends of measurements with high temporal resolution of PM2.5 and atmospheric particles with diameter smaller than 10 µm (PM10) in rural and urban locations are compared.

 

Regional and long-range transported aerosols and precursors hereof contribute to the particle number concentration in the submicrometer size range. The highest relative contribution from long-range transported particles is found at rural background locations and smaller relative contributions at other locations that are more influenced by local sources. For these reasons, long-range transported particles make up a smaller relative fraction at the suburban site (HVID) and urban background site (HCØ) and an even smaller fraction at the urban curbside station (HCAB), where highest particle number concentrations are measured due the significant contributions from local traffic. A trend of decreasing concentrations is observed at all stations when considering time periods of the order of a decade. From 2018 to 2019, particle number concentrations decreased at all stations. Decreasing trends from 2017-2018-2019 were found for HCAB and HVID, whereas a less consistent trend characterized RISØ and HCØ, where concentrations in 2018 exceeded those in 2017 and 2019. These changes were observed for both a fraction of the ultrafine particles (41 - 110 nm in this study) and for particles in the range 110 – 478/550 nm. It should be noted that 2018 was an unusually dry year. The summer precipitation was thus about 40% lower than the similar summer precipitation in 2017 and 2019.

 

With respect to high temporal resolution measurements of particulate mass, both PM2.5 and PM10 decreased at the urban curbside (HCAB) between 2017 and 2018 and further between 2018 and 2019. Likewise, the PM10 concentrations were observed to decrease between 2017 and 2018 and further between 2018 and 2019 at curbside in the second largest Danish city Aarhus as well as at rural site RISØ. The PM10 particle mass at HCAB (27 µg/m3) is in 2019 doubled of what is found at the rural location RISØ (13 µg/m3). Analyses of PM data with high temporal resolution is used to determine contribution from long-range transport and to analyze weekly variation, which is the result of the variation in traffic at the Copenhagen curbside.

 

The annual mean EC concentration at HCØ in 2019 was 0.32 µg/m3, which was 22% higher than at the rural site RISØ (0.26 µg/m3). The annual mean EC concentration at the suburban location HVID was 43% higher than the rural site. Thus, ambient PM2.5 contained more EC at the suburban site than in Copenhagen urban background. EC averaged 1.0 µg/m3 at urban curbside HCAB corresponding to an increment of about a factor of 4 from the rural site RISØ. EC changed 3-6% at RISØ, HCØ and HVID from 2017 to 2019, whereas EC decreased by 13% at HCAB during the same time period.