La pollution de l’air extérieur et ses effets sur la santé

• Particles cause respiratory and cardiovascular disorders. They are associated with increased mortality from cancer, respiratory disease, and cardiovascular disease. • Since October 2013, ambient air particles have been classified as a carcinogen by the International Agency for Research on Cancer (IARC).

The most vulnerable populations are pregnant women, newborns, children, older adults, and anyone with cardiovascular or respiratory disease, diabetes, or obesity.

• The presence of particles in the respiratory tract depends on their size: • the largest particles with a diameter greater than 5 micrometers are retained in the nasal region; • the finest particles, less than 1 micrometer, can reach the lungs and persist there.

Once in the air, nitrogen monoxide becomes nitrogen dioxide, a gas that irritates the bronchi and promotes asthma attacks and lung infections. Asthmatic people and young children are more sensitive to this pollutant.

These pollutants are emitted by humans through heating, vehicle engines, industrial processes, and nitrogen fertilizers. They are also emitted by natural elements such as volcanoes, lightning, and dry soils.

Ozone is a gas essential to terrestrial life present in the upper atmosphere to protect against the sun's ultraviolet rays. In the lower layers of the atmosphere, ozone is conversely a harmful air pollutant for human health.

Ozone can penetrate deep into the respiratory tract. Exposure to ozone most often causes dry cough and respiratory discomfort.

In the long term, this pollutant has cardiovascular effects. It can lead to asthma development and increases respiratory mortality.

Ozone also has harmful effects on vegetation, notably reduced crop yields for certain crops, and on some materials.

Benzene is one of the most harmful gases; it belongs to the family of "volatile organic compounds." Strong or regular exposure can cause critical effects on blood cells. Benzene has been classified as a carcinogen since 1987.

More broadly, the family of "volatile organic compounds," such as benzene, contributes to the formation of pollutants harmful to health, such as fine particles, through reaction with sunlight. This explains fine particle pollution that sometimes occurs during very sunny weather.

Sulfur dioxide is a pollutant that irritates the respiratory tract, eyes, and skin. It can cause coughing and asthma. Children and people with existing chronic respiratory problems are particularly sensitive.

• Sulfur dioxide causes acid pollution by combining with other pollutants such as nitrogen oxide. • This acid pollution can alter the chemical balance of watercourses, lakes, soils, or forests by falling with rain or wind.

This family comprises about one hundred molecules. Many of these molecules are present in the atmosphere in gaseous and particulate form. Benzo[a]pyrene is one of the best known. It is classified as a definite carcinogen. Others are also classified as probable or possible carcinogens.

Currently, their effects on human health are only partially known. Available data show that some can cause irritation, reduced respiratory capacity, and cancer development, particularly affecting the liver, blood, and reproductive system.

In ambient air, heavy metals are present in particulate and gaseous form. Heavy metals can be inhaled directly or ingested when the food chain is contaminated (through soils, water, or food).

In humans, they can affect the nervous system, kidneys, liver, or lungs. Some heavy metals, such as cadmium, arsenic, nickel, and chromium, are carcinogenic.

Carbon monoxide is a colorless, odorless, and highly toxic gas. It poses a particular danger to health indoors.

Its level in the air is increased by poor ventilation, for example in traffic jams in tunnels, with idling engines in parking lots, in homes, or by poor exhaust evacuation. Carbon monoxide can cause mild symptoms such as dizziness or headaches, but also cardiovascular or neurological problems and can even lead to comas or death in the most severe cases.

This gas contributes to acidification of the air, soils, and watercourses, and to ozone formation in the lower layers of the atmosphere.

Ammonia is an irritating gas with a pungent odor; it burns the eyes and lungs. It is toxic when inhaled at high levels, and even fatal at very high doses.

It causes excessive algae and plant growth and acidifies water and soils. It is also a gas that can form fine particles by combining with other substances, which will impact the environment and health.