Articles | Volume 16, issue 2
Atmos. Chem. Phys., 16, 715–738, 2016

Special issue: Aerosol-Cloud Coupling And Climate Interactions in the Arctic...

Atmos. Chem. Phys., 16, 715–738, 2016

Research article 21 Jan 2016

Research article | 21 Jan 2016

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

L. M. Zamora1,2, R. A. Kahn1, M. J. Cubison3, G. S. Diskin4, J. L. Jimenez3, Y. Kondo5, G. M. McFarquhar6, A. Nenes7,8,9, K. L. Thornhill4, A. Wisthaler10,11, A. Zelenyuk12, and L. D. Ziemba4 L. M. Zamora et al.
  • 1NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • 2Oak Ridge Associated Universities, Oak Ridge, TN, USA
  • 3CIRES and Dept. of Chemistry and Biochemistry, University of Colorado, Boulder, CO, USA
  • 4NASA Langley Research Center, Hampton, VA, USA
  • 5National Institute of Polar Research, Tokyo, Japan
  • 6University of Illinois at Urbana-Champaign, Urbana, IL, USA
  • 7Georgia Institute of Technology, Atlanta, GA, USA
  • 8Foundation for Research and Technology – Hellas, Patras, Greece
  • 9National Observatory of Athens, Athens, Greece
  • 10Department of Chemistry, University of Oslo, Oslo, Norway
  • 11Institute for Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Austria
  • 12Pacific Northwest National Laboratory, Richland, WA, USA

Abstract. 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 ( ∼  0.02 g m−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, 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 W m−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. 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.

Short summary
Based on extensive aircraft campaigns, we quantify how biomass burning smoke affects subarctic and Arctic liquid cloud microphysical properties. Enhanced cloud albedo may decrease short-wave radiative flux by between 2 and 4 Wm2 or more in some subarctic conditions. Smoke halved average cloud droplet diameter. In one case study, it also appeared to limit droplet formation. Numerous Arctic background Aitken particles can also interact with combustion particles, perhaps affecting their properties.
Final-revised paper