What is air pollution?
Coming mainly from the 3 million vehicles that pass through Paris every day, it is made up of many pollutants and quantiﬁed by the following few regulated indicators:
Nitrogen dioxide (NO2)
In Paris, two thirds of the nitrogen dioxide content comes from road emissions and is still twice as high as the regulations in the vicinity of traffic and slightly above the public health objectives for ambient air. In total, about 3.5 million people in Ile-de-France are exposed to air that exceeds the quality objective for this pollutant, mainly in Paris and the inner suburbs.
It also contributes to the mechanism that leads to the formation of ozone, a secondary tropospheric pollutant.
Although at high altitudes the ozone layer is vital for filtering ultraviolet rays, at ground level ozone is harmful to human health and the environment and contributes to the greenhouse effect.
Ozone is a secondary pollutant resulting from the chemical transformation, under the action of the sun, of primary pollutants emitted by road traffic, in particular NO2, and hydrocarbons (petrol vapours, glues, solvents, paints, etc.) both for industrial and domestic use.
Levels have almost doubled in fifteen years in the Parisian agglomeration, and ozone is the main cause of pollution peaks in summer.
Fine dust (PM 10 and PM2.5)
These airborne particles, with an average diameter of less than 10 and 2.5 micrometres, are toxic because they enter deep into the respiratory system. They can carry allergenic, irritating and carcinogenic compounds and cause asthma and cardiovascular disease. They are emitted partly by diesel vehicles, most of which do not have a particle filter, but also by the abrasion of tyres, brakes and road surfaces, as well as by incinerators, heating, air conditioning and factories. They are also produced by chemical reactions of gases with each other, resuspended in the air and then transported over long distances. Dust levels are highest in the vicinity of traffic.
What are the consequences of pollution?
On the population
Everyone is a victim of local pollution. It is harmful to health, especially for fragile or sensitive populations, such as children, the elderly and the sick. Every year in Europe, 400,000 people die prematurely because of particulate matter levels.
Daily pollution levels have a greater impact on health than one-off pollution peaks. The impact of chronic particulate pollution is comparable to that of passive smoking. Nevertheless, during pollution peaks, admissions to emergency departments for respiratory problems increase.
On the environment
Pollution modiﬁes ecosystems: tree growth slows down, sensitive species regress or even disappear.
Pollution degrades the city: houses and monuments are blackened by particles and degraded by acid chemical reactions.
Pollution changes the climate: the composition of the atmosphere is modified and some pollutants contribute to global warming.