During summer 2003, large areas of the West Canada (Alberta and British Columbia between 50°N and 60°N and between 105°W and 130°W) have undergone very important forest fires, which were detected by Total Ozone and Mapping Spectrometer (TOMS) and MODerate resolution Imaging Spectroradiometer (MODIS). Many Stratospheric Aerosol and Gas Experiment (SAGE) III measurements obtained during this summer and over this region exhibit enhanced aerosol extinctions in the low stratosphere. SAGE III instrument measures the transmitted light through the earth limb using the solar occultation method. Inversion of transmission measurements allows retrieving vertical profiles of concentration of minor gases and vertical profiles of aerosol extinction coefficient at several wavelengths (from 384 to 1545 nm) in the stratosphere.
We have analyzed the aerosol spectral extinctions measured during correlative SAGE III events to observe the impact of these biomass burnings on the properties of stratospheric aerosols. We have inferred the aerosol microphysical properties (effective radius, number density, surface area density) assuming two different compositions corresponding to background (sulphate) and biomass burning aerosols. We have also compared the results to values obtained during unperturbed periods. It is found that a large number of aerosols was injected in the stratosphere but we cannot distinguish between both types of aerosols.