Aerosols detection for urban air pollution monitoring

International audienceIn the context of reducing the impact of atmospheric pollution on public health in cities. Previous studies have shown that optical sensors aboard satellites may be sensitive to the level of pollution because of the relation between radiances and aerosol loading and especially particulate matter (PM). The purpose of this paper is to add to this evidence by studying cloud-free satellite images and ground measurements, and then to show that urban aerosols concentrations variations can be detected and quantified by the means of satellite images. We used the radiative transfer model (6S). We simulated the reflectance at pixel level in the Landsat-TM bands. The effects and contributions of parameters (H2O content, O-3 content, albedo, aerosols and atmosphere optical thickness) are studied thanks to experimental design approach. Change in aerosol loading is the major contributor to change in reflectance. We thus demonstrate and quantify the sensitivity of reflectance to PM. We find that channel TM4 (similar to 815 nm) of Landsat is the appropriate band. However, when taking into account the gain of the sensor, we recommend TM1. On TMl image, a difference of 71 DN (digital number) represents a variation of 120 mu g/m(3). The minimal concentration variation detectable is around 2.6 mu g/m(3). Results from observations (ground measurements and DN on satellites images) are in good agreement with simulations. In particular, an empirical model that converts DN into [PM] confirms simulations