Airborne measurements in the plumes from three prescribed burns of conifer slash showed the number concentration-size spectra to be biomodal with peaks at about 0.1 and about 0.5 micrometer. The mass distribution was sharply peaked at about 0.3 micrometer where over 80% of the mass of the particles in the plume resided. Most of the particles in the plumes were of primary rather than secondary origin. The burns emitted particulate mass into the atmosphere at rates of 0.1-15/kgs during the active burning phase. The average density of the particles ranged from 0.75 to 1.34 g/cc. Estimates of particle emission factors for the burns ranged from 0.2 to 2% higher values being associated with higher fuel consumption rates. The burns were prolific sources of cloud condensation nuclei (CCN), producing about 10 to the 10th power - 10 to the 11th power CCN per gram of wood consumed. The CCN resulted in anomalously high concentrations of water droplets greater than 10 micrometer diameter in the cumulus clouds produced by the burns. Ozone concentrations near the tops of the plumes reached values as high as 44 ppb above ambient values, the higher values generally being associated with high u.v. intensities. Peak concentrations of NO2 and NO in the plumes were about 60 ppb; the ratio of NOx/NO ranged from 1 to 3 SO2 was not found in the plumes.