Wildfire and the atmosphere: Modelling the chemical and dynamic interactions at the regional scale

• Published in: Atmospheric environment (1994) Vol. 51; pp. 234 - 249
• Main Authors: Strada, S., Mari, C., Filippi, J.-B., Bosseur, F.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-05-2012; Elsevier
• Subjects: aerosols; air; air quality; anthropogenic activities; Applied sciences; atmospheric chemistry; Atmospheric pollution; burning; coasts; emissions; emissions factor; energy; Exact sciences and technology; Fire spread; forest fires; heat transfer; Injection height; Mediterranean region; moderate resolution imaging spectroradiometer; Off-line coupled model; ozone; ozone depletion; photolysis; pollutants; Pollutants physicochemistry study: properties, effects, reactions, transport and distribution; Pollution; smoke; Smoke plume pollutants; vegetation; water vapor; wind; France; Mediterranean Basin; Fire spread; Smoke plume pollutants; Mediterranean region; Off-line coupled model; Injection height; Pollutant behavior; Regional scope; Air quality; Impact study; Plume; Aerosols; Air pollution; Vegetation fire; Atmospheric dispersion; Forest fire; Concentration distribution
• ISSN: 1352-2310; 1873-2844
• DOI: 10.1016/j.atmosenv.2012.01.023

Forest fires release significant amounts of trace gases and aerosols into the atmosphere. Depending on meteorological conditions, fire emissions can efficiently reduce air quality and visibility, even far away from emission sources. In 2005, an arson forest fire burned nearly 700 ha near Lançon-de-Provence, southeast France. This paper explores the impact of this Mediterranean fire on the atmospheric dynamics and chemistry downwind of the burning region. The fire smoke plume was observed by the MODIS-AQUA instrument several kilometres downwind of the burning area out of the Mediterranean coast. Signatures of the fire plume on air pollutants were measured at surface stations in southeastern France by the air quality network AtmoPACA. Ground-based measurements revealed unusually high concentrations of aerosols and a well marked depletion of ozone concentrations on the day of the fire. The Lançon-de-Provence fire propagation was successfully simulated by the semi-physical fire spread model ForeFire. ForeFire provided the burnt area at high temporal and spatial resolutions. The burnt areas were scaled to compute the fire heat and water vapour fluxes in the three-dimensional meso-scale non-hydrostatic meteorological model MesoNH. The simulated fire plume kept confined in the boundary layer with high values of turbulent kinetic energy. The plume was advected several kilometres downwind of the ignition area by the Mistral winds in accordance with the MODIS and AtmoPACA observations. The vertical plume development was found to be more sensitive to the sensible heat flux than to the fire released moisture. The burnt area information is also used to compute emissions of a fire aerosol-like tracer and gaseous pollutants, using emission factors for Mediterranean vegetation. The coupled model simulated high concentrations of the fire aerosol-like tracer downwind of the burning zone at the right timing compared to ground-based measurements. A chemical reaction mechanism was coupled on-line to the MesoNH model to account for gaseous chemistry evolution in the fire plume. High levels of ozone precursors (NOx, CO) were simulated in the smoke plume which led to the depletion of ozone levels above and downwind of the burning zone. This depletion of ozone was indeed observed at ground-based stations but with a higher impact than simulated. The difference may be explained by the simplified design of the model with no anthropogenic sources and no interaction of the smoke aerosols with the photolysis rates. Ozone production was modelled tens of kilometres downwind of the ignition zone out of the coast.
► We investigate the impact on gaseous air pollutants downwind of a Mediterranean wildfire. ► We use the “off-line” coupling between an atmospheric model and a fire spread model. ► The plume rise is more sensitive to the sensible heat flux released by the fire. ► High concentrations in ozone precursors are simulated close and downwind of the fire. ► The depletion of ozone is reproduced in the smoke plume near and downwind of the fire.