The World Health Organization (WHO) says 3 million people are killed worldwide by outdoor air pollution annually from vehicles and industrial emissions, and 1.6 million indoors through using solid fuel. Most are in poor countries. One study says 7-20% of cancers are attributable to poor air and pollution in homes and workplaces.
Wikipedia discusses air pollution
Research published in 2005 suggests that 310,000 Europeans die from air pollution annually. Direct causes of air pollution related deaths include aggravated asthma, bronchitis, emphysema, lung and heart diseases, and respiratory allergies.
Combustion-fired power plants (coal-fired power plants contribute 40% of world's sulphur and mercury).
A PDF by the World Health Organization on air pollution
A color PDF report on environmental causes of different diseases. 1.5 million deaths per year from respiratory infections attributable to the environment.