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Environmental effects of pollutants from coal combustion. 2, The Colstrip, MT Power Plant
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1981
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Description:Aerosol samples from the plume of the Colstrip, MT, power plant were analyzed for the presence of sulfates and nitrates with the transmission electron microscope using the BaCl2 and Nitron tests. Almost all particles of r < 0.3 pm that were collected 8 km (5 mi) or more downwind from the plant were found to contain sulfate and many were exclusively sulfate, without a mineral nucleus. Many of the particles of r > 1 pm have an adsorbed layer of sulfate. There are few nitrate-containing particles of r < 0.3 pm; most nitrate-containing particles are found to have r > 0.5 pm. The explanation is that N02, formed from the oxidation of NO, is itself readily oxidized to HN03 by OH in the vapor phase or by H20 in solution droplets. The HN03, or its mineral salt, is very hygroscopic and readily absorbs H20 from the atmosphere, thus forming large particles. In plume samples collected ~ 1.6 km (1 mi) downwind and analyzed with the scanning electron microscope with energy dispersive X-ray analysis, two-thirds of the particles of r > 0.1 pm were spherical. Almost all of the spherical particles contained both Si and Ca, with about half containing S. Particle flux measurements showed that the formation rate of particles in the plume is ~ 1016 s 1, with variation depending upon solar energy input and temperature, in addition to the emission rate of S02. This formation rate is satisfied with a conversion rate of S02 to sulfate of ~ 1 percent per hour. Most of the new volume formation shows up quickly in the accumulation mode, apparently through the mechanisms of gas deposition on existing aerosols, or by rapid growth of nuclei mode particles through coagulation. On the order of 90 percent of the new volume (at least regarding particles of r < 0.25 pm) is in the accumulation mode particles, modal radius about 0.06 pm. The modal radius increases with increasing reaction time, while the number of particles per unit volume decreases because of dilution and coagulation. Plume profile measurements provided width (y) and thickness (z) dimensions that could be compared to the estimations obtained from numerical plume models. The predicted width was usually less than measured, whereas the predicted thickness was much larger than measured. The differences between predicted and measured vertical dimensions are partly the consequence of the strong dependence of vertical extent on atmospheric stability. Tracking of the plume of the Col strip power plant plume with the aircraft provided some examples of plume trajectories that were apparently influenced by the underlying terrain by being diverted by as much as 20° from the wind direction at plume altitude, or by being ducted along a valley. Ice nuclei measurements on plume samples, as done with the filter and the acoustic counter methods are in conflict, with the former method indicating no difference in ice nucleus concentrations between plume and ambient atmosphere, and the latter showing an increase of an order of magnitude, or more, in the plume. The difference in response between the two methods may be due to the deactivation of the deposition and condensation-followed-by-freezing modes of nucleation by the surface adsorption of soluble sulfates. The Hay Coulee field site was apparently exposed to the power plant plume for a total of about 30 h during 340 h of observation from 20 August to 3 September 1977. Plume exposures were characterized by wide variations of plume constituent concentrations, varying from near background to maximum values within minutes. For 21 different plume exposure periods, the maximum condensation nuclei concentrations were 12.2 ± 9.8 x 103 cm 3 (mean and 1 sigma standard deviation).
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