Aerosol size distributions and aerosol volume formation for a coal-fired power plant plume

Abstract

During the summer of 1976, the plume from the Labadie power plant near St. Louis, Missouri was mapped on two days using an instrumented aircraft. The mapping consisted of measuring horizontal and vertical concentration profiles of both aerosol and gas contaminates for cross-sections of the plume. Measurements were made for plume travel times of up to 2 h and distances downwind of up to 50 km. Aerosol size distribution determinations were made in both the plume and surrounding background air mass. Characterization of these distributions was done in terms of two additive log-normal functions: one describing nuclei less than 0.03 μm in size and the second describing accumulation mode aerosol between 0.03 and 1.0 μm. On the average, results show that distribution of the nuclei volume for aerosol size less than 0.03 μm in both plume and background can be parameterized with a geometric mean size of 0.021 ± 0.005 μm and a geometric standard deviation of 1.5 ± 0.1. Total nuclei volume is found to be about 1% of total submicron aerosol volume. For aerosol larger than 0.03 μm, the geometric mean size of aerosol volume distributions in a daytime plume under uniform meteorological conditions was found to be 0.18 ± 0.02 μm. This is significantly different from the 0.23 ± 0.01 μm measured for background air. The dispersion of the distribution in this size range, measured by a geometric standard deviation of 1.92 ± 0.04, does not change significantly from in-plume to background. For a plume, measured in a morning transition period where average aerosol volume concentrations reached 87 μm 3cm −3, average volume mean geometric size for in-plume aerosol was 0.15 ± 0.01 μm vs 0.18 ± 0.01 μm in the background. Here, dispersion of the size distribution was narrower in the plume, with σ g = 1.63 ± 0.04 vs 1.86 ± 0.03 for background aerosol. Together with the integral Aitken nuclei concentration and b scat values, the aerosol size distribution measurements have been used to reconstruct the aerosol time history, up to two hours, for the various plumes investigated. Total aerosol volume flow through each cross-section of the plume has been calculated. When corrected for background levels, this flow is generally found to increase with time from levels as low as 60 cm 3s −1 to about 400 cm 3s −1. Assuming the excess volume formed is sulfuric acid in equilibrium with water vapor at the ambient r.h., we obtain an average SO 2 conversion rate of 0.7 ± 0.4% h −1 for the first 2 h of plume development.