Biomass Burning Smoke Influences Clouds over the Western U. S.
Abstract
Small cumulus clouds over the western United States were measured via
airborne instruments during the wildfire season in summer of 2018.
Statistics of the sampled clouds are presented and compared to smoke
aerosol properties. Cloud droplet concentrations were enhanced in
regions impacted by biomass burning smoke, at times exceeding 3,000
cm-3. Images and elemental composition of individual smoke particles and
cloud droplet residuals are presented and show that most are dominantly
organic, internally mixed with some inorganic elements. Despite their
high organic content and relatively low hygroscopicity, on average about
half of smoke aerosol particles >80 nm diameter formed
cloud droplets. This reduced cloud droplet size in small, smoke-impacted
clouds. A number of complex and competing climatic impacts may result
from wide-spread reductions in cloud droplet size due to wildfires
prevalent across the region during summer months.