National Geographic defines pollution as the introduction of harmful materials into the environment.
Pollution is caused by a lot of things such as car and truck exhaust, fumes, factories, dust, pollen, mold spores, ect...
Pollution isn't only in the air, but also in the water and in the ground.
Pollution is one of the biggest problems nowadays,...

A carbon footprint is a measure which expresses how much greenhouse gas an activity, a product or a service produce.The gases which we have to include when we calculate the carbon footprint have been defined by the international protocol of Kyoto (enacted on 16th February 2005). They are:

Thermal pollution is an anomaly in water temperatures recorded within an ecosystem.

Radioactive pollution is the release of radioactive substances or high-energy particles into the air, water and soil, causing serious problems for the environment and the health of living organisms.

Air pollution is the introduction of chemical and gaseous substances into the air that change the structure and the natural composition of the earth's atmosphere.

Water pollution is the contamination of lakes, seas, rivers, aquifers etc. by inputs of substances that alter their quality and condition.