Ice nuclei emissions from biomass burning

Biomass burning is a significant source of carbonaceous aerosol in many regions of the world. When present, biomass burning particles may affect the microphysical properties of clouds through their ability to function as cloud condensation nuclei or ice nuclei. We report on measurements of the ice nucleation ability of biomass burning particles performed on laboratory-generated aerosols at the second Fire Lab at Missoula Experiment. During the experiment we generated smoke through controlled burns of 21 biomass fuels from the United States and Asia. Using a Colorado State University continuous flow diffusion chamber, we measured the condensation/immersion freezing potential at temperatures relevant to cold cumulus clouds (-30 degrees C). Smokes from 9 of the 21 fuels acted as ice nuclei at fractions of 1: 10,000 to 1: 100 particles in at least one burn of each fuel; emissions from the remaining fuels were below the ice nuclei detection limit for all burns of each fuel. Using a bottom-up emission model, we estimate that smokes that emit ice nuclei fractions exceeding 1: 10,000 particles can perturb ice nuclei concentrations on a regional scale.