Forest fire impact on air quality: the Lançon-De-Provence 2005 case

International audienceForest fires release significant amounts of gases and aerosols into the atmosphere. Depending on meteorological conditions, fire emissions can efficiently spoil air quality and visibility far away from the source. The aim of this study is to evaluate the fire impact on air quality downwind of the burning region in the Mediterranean zone. Wildfire behaviour is simulated using a semi-physical model, ForeFire, based on an analytical resolution of the rate of spread. ForeFire provides the burnt area at high temporal and spatial resolutions; in the mesoscale non-hydrostatic meteorological model Meso-NH fire forcings, as heating and water vapor fluxes, are computed scaling them to the burnt area data given by ForeFire. A chemical scheme is coupled to Meso-NH to account for air quality evolution. Chemical emissions are scaled to the heating fluxes and based on emission factors for the Mediterranean vegetation. The model is used both in a 3D regional and 2D LES configurations. In 2005, an arson forest fire burned nearly 700 ha near Lançon-de-Provence, southeast France. ForeFire was successfully tested on this case study. Here, results from the coupled model, MesoNH-ForeFire, show the sensitivity of atmospheric dynamics and air quality situation to the coupling fire-atmosphere. Simulations put also on evidence how initial conditions and heat fluxes control fire emissions injection height. Finally, tracer distribution is simulated and its pattern shows that although the impact of the fire is visible several kilometres downwind of the burnt area, it remains confined within the planetary boundary layer. This behaviour is confirmed by comparing simulated aerosol particles concentrations with the air quality survey network available in southeastern France