1. Atmospheric environment and determinants of its quality

Air is the most essential element for life, and the one we consume in the greatest quantity: on average, an adult breathes 14 kg of air every day, while consuming around 1.5 kg of food and 2 kg of water. The atmosphere also plays a major role in regulating climate and maintaining the biosphere's living conditions. However, air quality is not constant over time and space, as its composition results from complex balances between, on the one hand, the constant input of matter from natural sources or human activities and, on the other hand, the continuous elimination and recycling of this matter through various physical and chemical mechanisms (dry and wet deposition of gases and particles, transformations in the atmosphere, assimilation by vegetation and oceans, etc.). If the balance of these exchanges is disrupted –, particularly as a result of human activity –, the composition of the air...