Air pollution has many sources and their mix varies by place. Common categories include transport, power generation and industry, household cooking and heating with polluting fuels, and municipal and agricultural waste burning.
WHO identifies cleaner transport, energy, industry and waste management as areas for reducing outdoor air pollution. Many sources require coordinated policy and infrastructure action beyond an individual's control.
A station reading alone cannot identify a pollution source or establish the impact of a policy. Source contributions need evidence specific to the place, period and method.