12 May 2023
 | 12 May 2023

Increase in precipitation scavenging contributes to long-term reductions of black carbon in the Arctic

Dominic Heslin-Rees, Peter Tunved, Johan Ström, Roxana Cremer, Paul Zieger, Ilona Riipinen, Annica Ekman, Konstantinos Eleftheriadis, and Radovan Krejci

Abstract. Black carbon (BC), the most efficient atmospheric aerosol for absorbing light in the visible spectrum, exerts a warming effect on a region undergoing unprecedented climatic changes. Here, BC is studied indirectly using filter-based methods to ascertain aerosol light absorption parameters. We investigated long-term changes using a harmonised 21-year data set of light absorption measurements, in conjunction with air mass source analysis. The measurements were performed at Zeppelin Observatory (ZEP), Svalbard, from 2002 to 2022. We report a statistically significant (s.s.) decreasing long-term trend for the light absorption coefficient, measured at the site for the entirety of the data set. However, the last 7 years, 2016–2022, showed a slightly increasing s.s. trend for the haze season. In addition, we observed an increasing trend in the single scattering albedo from 2002 to 2022. Five distinct source regions were identified; the trends involving air masses from the five regions showed decreasing absorption coefficients, except for the air masses influenced by emissions from Eurasia. We show that the changes in the occurrences of each transport pathway cannot explain the reductions in the absorption coefficient observed at the Zeppelin station; an increase in contributions of air masses from more marine regions, with lower absorption coefficients, is compensated by the influence from high-emission regions. Along with aerosol optical properties, we also show an increasing trend in accumulated surface precipitation experienced by air masses en route to the Zeppelin Observatory. We argue that rainfall, as a sink of aerosol, plays a role in the long-term trends in the absorption coefficient, explaining approximately a quarter of the overall trend. A decreasing trend in the scavenging ratio further suggests an increase in the aerosol removal processes. We note that there is an increasing potential influence from active forest fires, particularly in the last few summers (i.e. 2015–2022). Active fires have been shown to have a significant impact on the mean seasonal absorption coefficient especially during northern hemispheric summer. However, no noticeable alteration in annual long-term trends can be observed.

Dominic Heslin-Rees et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-940', Anonymous Referee #1, 19 Jun 2023
    • AC1: 'Reply on RC1', Dominic Heslin-Rees, 25 Sep 2023
  • RC2: 'Comment on egusphere-2023-940', Anonymous Referee #2, 27 Jun 2023
    • AC2: 'Reply on RC2', Dominic Heslin-Rees, 26 Sep 2023

Dominic Heslin-Rees et al.

Dominic Heslin-Rees et al.


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Short summary
Light-absorbing atmospheric particles (e.g. black carbon (BC)) exert a warming effect on the Arctic climate. We show that the amount of particle light absorption decreased from 2002 to 2022. We conclude that in addition to reductions in emissions of BC, wet removal plays a role in the long-term reduction of BC in the Arctic, given the increase in surface precipitation experienced by air masses arriving at the site. The potential impact of biomass-burning events is shown to have increased.