Where is air pollution worst?

* Major cities: Air pollution is often worst in major cities, where there is a high concentration of vehicles, factories, and other sources of pollution.

* Industrial areas: Areas with a lot of industry are also often heavily polluted, due to the emissions from factories and other industrial activities.

* Areas near highways or airports: Areas near highways or airports can also be heavily polluted, due to the emissions from vehicles.

* Low-income areas: Low-income areas are often disproportionately affected by air pollution, due to a number of factors, including a lack of access to green space, a higher concentration of polluting industries, and a lack of resources to invest in pollution control measures.

* Developing countries: Air pollution is also a major problem in many developing countries, where there are often fewer regulations on pollution and a lack of resources to invest in pollution control measures.