Formation of NO2 in Power-Plant Plumes: Measurements and Modelling

摘要

Nitrogen oxides are air pollutants involved in both acid deposition of e.g. HNO3 and formation of photochemical oxidants, e.g. ozone and peroxy acetyl nitrate (PAN). Conventional power plants are important sources of NO. After emission, NO is oxidized by ozone into NO2 during dispersion of the flue-gas plume in the atmosphere. Modelling of the fairly rapid conversion process is hampered by the interaction of the mixing process and the chemical kinetics. The contribution concerns the formation of nitrous oxide in power plant plumes and the evaluation of field measurements by means of a gaussian-type reactive plume model. The model assumes homogeneous mixing and photostationary equilibrium in the plume. The results showed that the NO2/NOx ratio can be calculated within the limits of reliability in many cases. A box-type model which incorporates inhomogeneous mixing was used to model the measured deviations of photostationary equilibrium in the plume. Measured deviations of the equilibrium can be explained by two causes, i.e. the various time rates at which the physical processes of dispersion and mixing, and the chemical processes of molecular reactions occur, and an extra contribution of ozone in parcels of unmixed ambient air in the plume.