Sulfur dioxide (SO₂) is a colourless gas. Major sources include burning sulfur-containing fuels, such as coal and oil, for heating, electricity generation and industrial processes.

EEA: common air pollutants · WHO: air pollutants and health

Nitrogen dioxide (NO₂) comes mainly from fuel burning in vehicles, heating, power generation and industry. Gas stoves and other fuel-burning appliances can also release it indoors. It contributes to the formation of ozone and fine particles in the atmosphere.

WHO: air pollutants and health