Air quality and meteorology
From one day to the next, ambient air pollution can vary enormously (concentrations 5 to 20 times higher than average). These variations are explained by the variability of atmospheric emissions but also by the complexity of meteorological phenomena which control the dispersion of pollutants or, on the contrary, their accumulation.
- The wind and the rain promote the dispersion, mixing and leaching of pollutants. Luckily, the Paris metropolitan area is located in the plain and generally benefits from a rainy and windy oceanic climate (predominant westerly winds).
- In winter, persistent anticyclonic situations (high atmospheric pressure, calm weather and clear skies) causes so-called emergency situations.temperature inversion. Indeed, anticyclones associated with weak winds contribute to the formation of a lid of warm air above the city, called a temperature inversion. It prevents the dispersion of pollutants and promotes the stagnation and accumulation of essentially primary pollutants, such as nitrogen oxides and particles, emitted above the agglomeration.
- In summer, anticyclonic situations and more particularly heatwave periods are accompanied by ozone peaks. Under the action of the sun's UV rays and in cases of high heat, nitrogen oxides (NOx) and volatile organic compounds (VOCs) promote and accelerate the formation of ozone (O3). Ozone is thus called a “summer” pollutant. These concentrations are correlated with sunshine and high temperatures.
