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Preprints
https://doi.org/10.5194/acp-2020-201
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-201
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  29 Apr 2020

29 Apr 2020

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A revised version of this preprint is currently under review for the journal ACP.

Spatiotemporal variation and trends of equivalent black carbon in the Helsinki metropolitan area in Finland

Krista Luoma1, Jarkko V. Niemi2, Aku Helin3, Minna Aurela3, Hilkka Timonen3, Aki Virkkula3, Topi Rönkkö4, Anu Kousa2, Pak Lun Fung1, Tareq Hussein1,5, and Tuukka Petäjä1 Krista Luoma et al.
  • 1Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, P.O. Box 68, 00014 Helsinki, Finland
  • 2Helsinki Region Environmental Services Authority, P.O. Box 100, 00066 Helsinki, Finland
  • 3Atmospheric Composition Research, Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, Finland
  • 4Aerosol PhysicsLaboratory, Faculty of Engineering and Natural Sciences, Tampere University, P.O. Box 692, 33014 Tampere, Finland
  • 5Department of Physics, The University of Jordan, 11942 Amman, Jordan

Abstract. In this study, we present results of 12 years of black carbon (BC) measurements at 14 different measurement sites around the Helsinki metropolitan area (HMA) and at one background site outside the HMA. The main local sources of BC in the HMA are traffic, and residential wood combustion in fireplaces and sauna stoves. All the BC measurements were conducted optically and therefore we refer to the measured BC as equivalent BC (eBC). Measurement stations were located at different types of environments that represented traffic environment (six sites), detached housing area (five sites), urban background (two sites), and regional background (two sites). The measurements of eBC were conducted during 2007–2018; however, the time period and the length of the time series varied from site to site. As expected, the largest annual mean eBC concentrations were measured at the traffic sites (0.67–2.64 μg m−3) and the lowest at the regional background sites (0.16–0.29 μg m−3). The annual mean eBC concentrations at the detached housing sites varied in the range of 0.64–0.80 μg m−3 and the annual mean eBC concentrations at the urban background sites varied in the range of 0.42–0.68 μg m−3. The clearest seasonal variation was observed at the detached housing sites, where the residential wood combustion increased the eBC concentrations during the cold season. Traffic rates and wood burning influenced the diurnal and weekly variations of eBC concentration in different types of environments. The dependency was not so clear for the other air pollutants, which were here NOx and mass of particles smaller than 2.5 μm (PM2.5). At four sites, which had at least four-year-long time series available, we observed that the eBC concentrations had statistically significant decreasing trends, which varied in the range of −10.4–−5.9 % yr−1. Compared to the trends determined at the urban and regional background sites, the absolute trends decreased the fastest at the traffic sites and especially during the morning rush hour. The relative long-term trends of eBC and NOx were similar to each other, and their concentrations decreased more rapidly than the concentration of PM2.5. The results indicate that especially the emissions from traffic have decreased in the HMA during the last decade. This shows that air pollution control, new emission standards and newer fleet of vehicles really have an effect in the air quality.

Krista Luoma et al.

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Krista Luoma et al.

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Short summary
This study collated black carbon measurements from 15 different sites located in southern Finland. Sites were classified as traffic, detached housing area, urban background, and regional background sites. The seasonal, weekly and diurnal variations of the black carbon concentration were associated with local emissions from traffic and residential wood burning. Decreasing trends for the black carbon concentration were observed and the trends were connected to decreases in traffic emissions.
This study collated black carbon measurements from 15 different sites located in southern...
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