Air

Ambient air is the mixture of gases that make up the earth's atmosphere. Its natural composition can be altered by the introduction of other gaseous, liquid or solid substances, thus giving rise to the phenomenon of air pollution.
These substances, referred to as air pollutants, can reach concentration levels that can cause harmful effects on people's health and, more generally, on the entire ecosystem. Air pollution in urban areas can have several effects: health risks mainly associated with the inhalation of gases and particles, accelerated deterioration of buildings (including monuments), and damage to vegetation and ecosystems.