Aerosol characterization at Colstrip, Montana, spring and fall, 1975

Aerosols in the Colstrip, Montana, atmosphere have been monitored prior to operation of a large coal-fired power plant to establish a baseline for future studies. This project is a part of EPA's Montana Coal-Fired Power Program. Observations showed total particle counts corresponding to a clean rural atmosphere, with typical Aitken nuclei counts of 1500 cm-3 near the surface and decreasing to less than 500 cm-3 a few hundred meters above the surface, but occasionally rising to more than 5000 cm-3. The ice nuclei count was twice as high as expected for this type of environment, and was apparently correlated with the rather high incidence of heavy metals found in aerosols collected on membrane filters. Calculations of the optical properties from these samples predict a slight cooling effect at the surface except when the ground is snow covered, when a slight warming can be expected. Airborne measurements of blackbody temperature under stable nightime conditions showed no variation with altitude, indicating the aerosols are presently generating little if any effect on surface temperatures. Acoustic sounder records show numerous occasions of temperature inversions higher than the 150 meter stacks, with some extending as high as 1000 meters and persisting all day. Optical turbidity measured in the Fall was consistent with values obtained in other rural environments in the high plains, averaging about .07. Preliminary results from the dual polarization lidar indicates that this will be a useful method for discriminating between dust and power plant effluent.