Generation of secondary pollutants in a power plant plume: A model study

Abstract

A plume model is developed where chemistry and meteorology of the boundary layer interact with a power plant plume which is given a spatial resolution in the cross wind direction. Ozone bulges are formed after 2 1 2 –3 h or more, with excess ozone 10–20 % above ambient levels in fair weather during summer for a plume comparable to the St. Louis Labadie power plant plume. The chemical activity peaks first on the plume fringes, later close to the central axis. Hydroxyl exceeds 13 × 10 6 molecules cm −3 within the plume after a few hours and the corresponding SO 2 to sulphate conversion rate ranges between 1 and 5%h −1. Nitric acid formation exceeds sulphuric acid formation during developed stages of the plume. Ambient emissions of nitrogen oxides and hydrocarbons representative for heavily populated areas tend to reduce the relative size of the ozone bulge compared to cases with lower emissions, and medium size power plants give rise to more excess ozone than larger plants. The ozone bulge disappears when the solar radiation is substantially reduced. The fate of the HSO x radicals and its involvement in odd hydrogen regeneration is essential in the understanding of the plume chemistry.