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Title: Aircraft-measured indirect cloud effects from biomass burning smoke in the Arctic and subarctic

The incidence of wildfires in the Arctic and subarctic is increasing; in boreal North America, for example, the burned area is expected to increase by 200–300% over the next 50–100 years, which previous studies suggest could have a large effect on cloud microphysics, lifetime, albedo, and precipitation. However, the interactions between smoke particles and clouds remain poorly quantified due to confounding meteorological influences and remote sensing limitations. Here, we use data from several aircraft campaigns in the Arctic and subarctic to explore cloud microphysics in liquid-phase clouds influenced by biomass burning. Median cloud droplet radii in smoky clouds were ~40–60% smaller than in background clouds. Based on the relationship between cloud droplet number (Nliq) and various biomass burning tracers (BBt) across the multi-campaign data set, we calculated the magnitude of subarctic and Arctic smoke aerosol–cloud interactions (ACIs, where ACI = (1/3) × dln(Nliq)/dln(BBt)) to be ~0.16 out of a maximum possible value of 0.33 that would be obtained if all aerosols were to nucleate cloud droplets. Interestingly, in a separate subarctic case study with low liquid water content (~0.02gm–3) and very high aerosol concentrations (2000–3000 cm–3) in the most polluted clouds, the estimated ACI value was only 0.05. In this case,more » competition for water vapor by the high concentration of cloud condensation nuclei (CCN) strongly limited the formation of droplets and reduced the cloud albedo effect, which highlights the importance of cloud feedbacks across scales. Using our calculated ACI values, we estimate that the smoke-driven cloud albedo effect may decrease local summertime short-wave radiative flux by between 2 and 4 Wm–2 or more under some low and homogeneous cloud cover conditions in the subarctic, although the changes should be smaller in high surface albedo regions of the Arctic. Furthermore, we lastly explore evidence suggesting that numerous northern-latitude background Aitken particles can interact with combustion particles, perhaps impacting their properties as cloud condensation and ice nuclei.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [3] ;  [5] ;  [6] ;  [7] ;  [4] ;  [8] ;  [9] ;  [4]
  1. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States); Oak Ridge Associated Univ., Oak Ridge, TN (United States)
  2. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)
  3. Univ. of Colorado, Boulder, CO (United States)
  4. NASA Langley Research Center, Hampton, VA (United States)
  5. National Institute of Polar Research, Tokyo (Japan)
  6. Univ. of Illinois at Urbana-Champaign, Urbana, IL (United States)
  7. Georgia Inst. of Technology, Atlanta, GA (United States); National Observatory of Athens, Athens (Greece); Foundation for Research and Technology - Hellas, Patras (Greece)
  8. Univ. of Oslo, Oslo (Norway); Univ. of Innsbruck, Innsbruck (Austria)
  9. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
OSTI Identifier:
1249367
Report Number(s):
PNNL-SA--112359
Journal ID: ISSN 1680-7324
Grant/Contract Number:
NNX12AC03G; NNX15AH33A; AC0576RL01830
Type:
Accepted Manuscript
Journal Name:
Atmospheric Chemistry and Physics (Online)
Additional Journal Information:
Journal Name: Atmospheric Chemistry and Physics (Online); Journal Volume: 16; Journal Issue: 2; Journal ID: ISSN 1680-7324
Publisher:
European Geosciences Union
Research Org:
Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 09 BIOMASS FUELS