The goal of the project is to obtain new data to quantify the potential ice nucleation activity and variability of biomass burning aerosols from fresh smoke plumes. Such data are critical additions, as laboratory studies cannot mimic the lofting of soil (and possibly biological) particles accompanying a large-scale fire, and higher fire temperatures from large-scale burns may impact the chemical composition of the smoke particles. Data will be collected primarily from prescribed burns in coordination with U.S. Forest Service collaborators, with a focus on the variation of ice nuclei (IN) with characteristics of the plumes, including total number and mass concentrations, as a function of temperature and processing relative humidity. One focus will be to determine if IN number concentrations relate to the total number concentrations of particles with equivalent diameters larger than 0.5 ?�m in the same manner as we have observed at many locations not heavily influenced by biomass burning. They also will explore further the relation between IN and aerosol chemical composition. To this end, chemical composition of the total aerosol will be determined, and the elemental composition of the ice nucleating fraction will be examined in the context of the total aerosol measurements. Measurements will be conducted both at the source and downwind of the burns to explore transformations of biomass burning IN due to atmospheric processing. A suite of biomass burning markers from the chemical composition measurements will be used to confirm that they are, in fact, sampling the plume. To explore the impact of atmospheric processing in a more controlled manner, they also will test the ice nucleating ability of artificially ‘aged’ smoke particles by coating biomass burning particles sampled at the burn source with sulfate and secondary organic aerosol generated from oxidizing ambient Volatile Organic Compounds (VOC) in the plume. Finally, they will attempt to sample smoke from regional wildfires of opportunity, when possible, using a mobile laboratory facility.