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Atmospheric soot : more polluting than expected
Soot is a set of chemical compounds produced by the incomplete combustion of fossil fuels (gasoline, diesel, fuel oil, kerosene) or biomass (wood, plants). It is also associated with pollution from urban areas. When produced, the solid particles of soot are released into the atmosphere where they remain in suspension (aerosols). In this form, this pollutant acquires a specific reactivity.
Under the direct action of sunlight, the reactivity of soot particles changes, and most importantly increases. For example, under solar irradiation, nitrogen dioxide, one of the pollutants responsible for the photochemical production of ozone, reacts with soot over very long periods and efficiently produces nitrous acid (HNO2), a precursor of atmospheric free radicals that accelerate ozone formation : more soot, more light … more ozone !
Furthermore, this chemistry also induces the formation of compounds called nitro-PAHs (Polycyclic Aromatic Hydrocarbons), known to be extremely toxic to human health… These nitrogen oxide "traps" are able to remain through the night, travel over long distances using the movements of air masses, and release these oxides under the effect of daylight to produce ozone in initially unpolluted areas. Hence the impact of this photochemistry of soot is not just a local concern.
Institut de recherches sur la catalyse et l’environnement de Lyon, CNRS-Université de Lyon 1
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