Measurements and modelling of reactions of nitrogen oxides in power-plant plumes at night

Abstract

Formation of NO 2, HNO 3, NO 3 − and SO 4 − in power-plant plumes at night has been studied on the basis of aircraft measurements and modelling. At night the plume could not easily be detected; it stayed very narrow and could be located either belor or above the nocturnal inversion layer. To facilitate detection of the plume at night, an electric field meter was installed in an aircraft through which the plume could be detected remotely. If the plume is located above the inversion layer at night, O 3-concentrations needed for the oxidation reaction with NO can be rather high and NO 2 can be formed. However, in this case the plume will not reach the ground and will not cause NO 2-concentrations at ground level. If on the other hand the plume is below the inversion in the mixing layer, O 3-concentrations will be low and oxidation of NO will therefore be slow, and not much NO 2 is formed in the mixing layer. The plume measurement have been compared with results of a reactive plume model which is based on a numerical solution of the diffusion equation in which chemical reactions have been added. Measurements and model calculations of the oxidation rate of NO are in good agreement. Supplementary calculations with the diffusion model regarding the formation of HNO 3 in power-plant plumes at night indicate that the only little—if any—HNO 3 is formed, which is in agreement with the measurements.