Air pollution is the presence of particles and gases in the atmosphere that can be harmful to humans, other living beings, and the environment. These particles and gases come from a variety of human and natural sources. Human sources include carbon emissions from factories, vehicle exhaust and planes, cigarette smoke, and even aerosol cans. Natural sources include pollen from plants, mold, wildfires, or ash from an erupting volcano (source).
The most common air pollutants are Carbon Monoxide, Particulate Matter, Ozone, Nitrogen Dioxide, and Sulphur dioxide. They mainly originate from fossil fuels, power plants, and cars (source). When these pollutants reach a certain concentration, they become a severe risk factor for humans – causing several health complications such as asthma, respiratory infections, heart disease, lung cancer, congenital disabilities, and in extreme cases, death. It is said that air pollution kills an estimated seven million people worldwide every year (source).
Air pollution is also detrimental to the natural environment. When pollutants suspended in the air eventually fall back to the ground, they contaminate soil and water, consequently killing plants, small trees and reducing crop yields. Haze, for example, is a type of visible air pollution that reduces the strength of solar rays and affects a plant’s ability to reproduce and photosynthesize (source).
Air pollution is often thought only to occur outside. However, many types of indoor air pollutants affect human health. Household pollutants, from burning substances like kerosene, wood, and coal to cook or heat a home, are one of the leading causes of diseases and premature death in developing countries (source).
Today, 9 out of 10 people breathe air that exceeds guideline limits set by the World Health Organization (WHO), with low- and middle-income countries suffering from the highest exposures (source). According to the WHO, the world's most polluted cities include Karachi, Pakistan; New Delhi, India; Beijing, China; Lima, Peru; and Cairo, Egypt.
There are several ways to fight air pollution: air quality standards, a carbon tax on carbon dioxide emissions, lowering our dependency on coal and transitioning to renewables, carbon capture technology, incentive programs to encourage people to transition to more fuel-efficient or electric vehicles, and more. Since the Clean Air Act of 1970, for example, aggregate national emissions of the most common pollutants dropped an average of 73% (source).