Measurements of gas-to-particle conversion in the plumes from five coal-fired electric power plants

Abstract

Airborne measurements of particles and trace gases have been obtained in the plumes from five coal-fired electric power plants situated in the West and Midwest of the United States. From these data, gas-to-particle (g-to-p) conversion rates are estimated from changes in total particle volume, changes in the ratio of the mass of particulate sulfur to the total mass of sulfur (particulate sulfur measured by two techniques), and from particle nucleation ∗ ∗ By nucleation we mean the formation of a particle of detectable size. Thus, our nucleation rate may or may not be the same as the rate of formation of molecular clusters from the gas phase. rates. The g-to-p conversion rates ranged from 0 to 5.7% ± 2.0% of SO 2 h −1 for travel times of 10–162 min. The data suggest differences between plants in the partitioning of g-to-p conversion products between condensation onto existing particles and the nucleation of new particles. The relationship between panicle surface area and the formation rate of particle volume at large reaction times in the plumes was similar to that found in smog chamber studies. Finally, the SO 2-to-particulate sulfate conversion rate was found to correlate well (correlation coefficient — 0.9) with a parameter indicative of the reaction of SO2 in the plumes with ambient OH radicals.