Chemical processes in a young biomass‐burning plume

Abstract

The photochemistry in young biomass‐burning plumes depends on the emissions from the fire and their mixing with the background atmosphere as well as on the actinic flux. In the present study a three‐dimensional plume model is used to investigate the photochemical evolution of a biomass‐burning plume during the first tens of minutes after the fire emissions have been released into the atmosphere. The model results represent the evolution of the plume from the Quinault prescribed fire conducted during the Smoke, Cloud, and Radiation‐C (SCAR‐C) experiment. The modeled ozone concentrations of about 70 ppb are close to observations. The main nitrogen reservoir species downwind of the fire are HNO3and peroxyacetyl nitrate, accounting for about ∼60% and ∼30% of the total nitrogen reservoir species, respectively. Photolysis of formaldehyde, which is emitted from the fire, is the primary source of radicals in the plume. Omitting the emissions of oxygenated volatile organic compounds in the modeled fire plume leads to unrealistically low ozone concentrations in the simulations. A nonabsorbing aerosol as well as the lower emission of NOxin the simulations enhance the radical concentration, the photochemical ozone formation, and the oxidation efficiency, at least at the timescales considered here. Further investigations of the atmospheric processes in young biomass‐burning plumes will increase our understanding of the interaction of transport and chemical processes not only in biomass‐burning plumes but also in other convective systems.