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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/amt-2020-192
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2020-192
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  25 Jun 2020

25 Jun 2020

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This preprint is currently under review for the journal AMT.

Comparison of co–located rBC and EC mass concentration measurements during field campaigns at several European sites

Rosaria E. Pileci1, Robin L. Modini1, Michele Bertò1, Jinfeng Yuan1, Joel C. Corbin1,a, Angela Marinoni2, Bas J. Henzing3, Marcel M. Moerman3, Jean P. Putaud4, Gerald Spindler5, Birgit Wehner5, Thomas Müller5, Thomas Tuch5, Arianna Trentini6, Marco Zanatta7, Urs Baltensperger1, and Martin Gysel-Beer1 Rosaria E. Pileci et al.
  • 1Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen PSI, Switzerland
  • 2CNR–ISAC—Italian National Research Council, Institute of Atmospheric Science and Climate, via Gobetti 101, 40129 Bologna, Italy
  • 3Netherlands Organisation for Applied Scientific Research (TNO), Princetonlaan 6, 3584 Utrecht, the Netherlands
  • 4European Commission, Joint Research Centre (JRC), Ispra, Italy
  • 5Leibniz Institute for Tropospheric Research (TROPOS), Permoserstrasse 15, 04318, Leipzig,Germany
  • 6Regional Agencyfor Prevention, Environment and Energy, Emilia–Romagna, 40122, Bologna, Italy
  • 7Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
  • anow at: Metrology Research Centre, National ResearchCouncil Canada, 1200 Montreal Road, Ottawa K1A 0R6, Canada

Abstract. The mass concentration of black carbon (BC) particles in the atmosphere has traditionally been quantified with two methods: as elemental carbon (EC) concentrations measured by thermal-optical analysis and as equivalent black carbon (eBC) concentrations when BC mass is derived from particle light absorption coefficient measurements. Over the last decade, ambient measurements of refractory black carbon (rBC) mass concentrations based on laser-induced incandescence (LII) have become more common, mostly due to the development of the Single-Particle Soot Photometer (SP2) instrument. In this work, EC and rBC mass concentration measurements from field campaigns across several background European sites (Paris, Bologna, Cabauw and Melpitz) have been collated and examined to identify the similarities and differences between BC mass concentrations measured by the two techniques. All EC concentration measurements in PM2.5 were performed with the EUSAAR-2 thermal-optical protocol. All rBC concentration measurements were performed with SP2s calibrated with the same calibration material as recommended in the literature. The median ratio between observed rBC and EC mass concentrations was 0.92, when considering all data points from all five campaigns, and the corresponding geometric standard deviation (GSD) was 1.5. The minimal and maximal observed values of median rBC to EC mass concentration ratios on single campaign level were 0.53 and 1.29, respectively. This shows that substantial systematic bias between these two quantities occurred during some campaigns, which also contributes to the large overall GSD. On single campaign level, the relative spread of individual rBC to EC mass concentration ratios was typically between a factor of 1.2 and 1.3 (1 GSD), which indicates fairly good precision of both methods.

Despite considerable variability of BC properties and sources across the whole data set, it was not possible to clearly assign reasons for discrepancies to one or the other method, both known to have their own specific limitations and uncertainties. However, differences in the particle size range covered by these two methods were identified as one likely reason for discrepancies. In particular, rBC to EC mass concentration ratios were found to be systematically less than unity, despite applying a correction for small BC cores that remain undetected by the SP2. This was observed when the rBC mass size distribution was shifted towards smaller modal diameter, which occurred during traffic emission dominated episodes.

Overall, the high correlation between rBC and EC mass concentrations indicates that both methods essentially quantify the same property of atmospheric aerosols, whereas systematic differences in measured absolute values by up to a factor of 2 can occur. This finding for the level of agreement between two current state-of-the-art techniques has important implications for studies based on BC mass concentration measurements, for example for the interpretation of uncertainties of inferred BC mass absorption coefficient values, which are required for modelling the radiative forcing of BC. Homogeneity between BC mass determination techniques is very important also towards a routine BC mass measurement for air quality or human health regulations.

Rosaria E. Pileci et al.

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Rosaria E. Pileci et al.

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Latest update: 04 Dec 2020
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Short summary
Black carbon, which is an important constituent of atmospheric aerosols, remains difficult to quantify due to various limitations of available methods. This study provides an extensive comparison of co-located field measurements applying two methods based on different principles. It was shown that both methods indeed quantify the same aerosol property – BC mass concentration. The level of agreement that can be expected was quantified and some reasons for discrepancy were identified.
Black carbon, which is an important constituent of atmospheric aerosols, remains difficult to...
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