On the relative contributions of NO 2 and particles to the color of smoke plumes

Abstract

This paper studies the relative influences of NO 2 absorption and particle scattering on plume appearance. Theoretical results are summarized in compact nomograms which permit the direct comparison of absorption and scattering effects. These show the strong variation of scattering effects with viewing angle and particle size. Available data from several coal and oil-fired power plants in the southwestern U.S. are collated and evaluated in the light of the theory. From the limited data base, it is concluded that particle scattering: (a) controls plume-horizon contrast under most conditions at the older coal-fired plants; (b) is an important near-stack plume colorant at oil-fired plants; (c) may be a significant plume colorant at coal-fired plants equipped with wet scrubbers and (d) does not contribute to brown plume color at coal-fired plants equipped with electrostatic precipitators. Throughout the paper, all results and data are expressed in forms which are invariant under plume dilution, so that fundamental optical relationships are not obscured by the large variations encountered in atmospheric transport and dispersion.