Air pollution is the collection of minute particles and gases which pollute all outdoor areas, including outdoor workplaces, parks, and beaches.  It is found almost everywhere in nature, from lakes to seawater and from glaciers to jungles. Pollution can result from natural processes, or the combined effects of human activities—such as waste burners, smelters, coal-fired power plants, factories, cars, diesel engines, industries, and other sources. Air pollution is a serious problem for our environment and global climate.

Air pollution causes health problems such as coughing, wheezing, or chest pain. In addition, it can cause a person to breathe more slowly and use more energy in breathing than a person without air pollution. The effects of air pollution are associated with public health interventions such as clean transportation and cleaner fuels.  Air pollution is a major public health problem. It is known to be one of the top five causes of disease and premature death globally.

The environmental organization Earth Day Network defines air pollution as "any change in background concentrations of a substance that threatens human health or welfare by reducing visibility, increasing skin cancer risk, or decreasing crop production". Air pollution has been connected to higher rates of asthma and other respiratory problems, premature death, heart disease, and even leukemia. The WHO estimates that over 1 million people die each year from breathing unhealthy air or from polluted water due to industrial processes or vehicles. Air pollution is a major cause of death around the world. It affects both the short-term and long-term outcomes of cancer, heart disease, and other diseases.