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Discussion papers | Copyright
https://doi.org/10.5194/acp-2018-587
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 14 Jun 2018

Research article | 14 Jun 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

High–Arctic aircraft measurements characterising black carbon vertical variability in spring and summer

Hannes Schulz1, Heiko Bozem2, Marco Zanatta1, W. Richard Leaitch3, Andreas B. Herber1, Julia Burkart4,a, Megan D. Willis4, Peter M. Hoor2, Jonathan P. D. Abbatt4, and Rüdiger Gerdes1,5 Hannes Schulz et al.
  • 1AlfredWegener Institute, Helmholtz Center for Polar and Marine Research, Bremerhaven, Germany
  • 2Institute of Atmospheric Physics, Johannes Gutenberg-University, Mainz, Germany
  • 3Environment and Climate Change Canada, Toronto, Ontario, Canada
  • 4Department of Chemistry, University of Toronto, Ontario, Canada
  • 5Physics & Earth Sciences, Jacobs University, Bremen, Germany
  • anow at: Aerosol Physics and Environmental Physics, University of Vienna, Austria

Abstract. The vertical distribution of black carbon (BC) particles in the Arctic atmosphere is one of the key parameters controlling its radiative forcing. Hence, this work investigates the presence and properties of BC over the high Canadian Arctic. Airborne campaigns were performed as part of the NETCARE project and provided insights into the variability of the vertical distributions of BC particles in summer 2014 and spring 2015. The observation periods covered evolutions of cyclonic disturbances to the polar dome that caused and changed transport of air pollution into the High–Arctic, as otherwise the airmass boundary largely impedes entrainment of pollution from lower latitudes. A total of 48 vertical profiles of refractory BC (rBC) mass concentration and particle size, extending from 0.1 to 5.5km altitude, were obtained with a Single–Particle Soot Photometer (SP2).

Generally, the rBC mass concentration decreased from spring to summer by a factor 10. Such depletion was associated with a decrease of the mean rBC particle diameter, from approximately 200nm to 130nm at low altitude. Due to the very low number fraction, rBC particles did not substantially contribute to the total aerosol population in summer.

Profiles analysed with potential temperature as vertical coordinate revealed characteristic variability patterns due to different balances of supply and removal of rBC in specific levels of the stable atmosphere. Kinematic back–trajectories were used to investigate transport pathways into these levels. The lower polar dome was influenced by low–level transport from sources within the cold central and marginal Arctic. During the spring campaign, a cold air outbreak over eastern Europe additionally caused northward transport of air from a corridor over western Russia to Central Asia that was affected by emissions from gas flaring, industrial activity and wildfires. This caused rBC concentrations between about 500 to 1800m altitude to gradually increase from 32 to 49ngm−3. The temporal development of transport to the level above, at around 2500m, caused the initially low concentration to increase from <15ngm−3 to 150ngm−3. Despite the higher concentrations in the upper level, significantly less rBC reached the High–Arctic relative to co–emitted CO. A shift in rBC mass–mean diameter, from above 200nm in the low–level transport dominated lower polar dome to <190nm at higher levels, indicates that rBC got affected by wet removal when lifting processes were involved during transport. The summer polar dome had limited exchange with the mid–latitudes. Air pollution was supplied from sources within the marginal Arctic as well as by long–range transport, but in both cases rBC was largely depleted in absolute and relative concentrations. Near the surface, rBC concentrations were <2ngm−3, while concentrations increased to <10ngm−3 towards the upper boundary of the polar dome. The mass–mean particle diameter of 132nm was smaller than in spring. The shape of the summer mean mass–size distribution, however, resembled the spring distribution from higher levels, which was depleted of particles >300nm due to nucleation scavenging.

Our work provides vertical, spatial and seasonal information of rBC characteristics in the High–Arctic polar dome, offering a more extensive dataset for evaluation of chemical transport models and for radiative forcing assessments than obtained before by any other aircraft campaign.

Hannes Schulz et al.
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Aircraft vertical profiles of black carbon (BC) aerosol from the coldest regions of the Arctic have shown systematic variability in different levels of the stably stratified polar dome. Moreover, a different balance of supply by transport (from gas flaring and wildfires) and wet removal of BC near the surface and at higher levels was apparent from changes in particle size and mixing ratios with CO during spring and summer. Summer concentrations were a factor 10 lower due to stronger wet removal.
Aircraft vertical profiles of black carbon (BC) aerosol from the coldest regions of the Arctic...
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