Air pollution can cause a variety of illnesses in humans, including asthma, lung cancer, heart disease and even reproductive and developmental disorders. It can also compromise the immune system by overworking the respiratory system and the body's natural defenses. Air pollution also contributes to global warming, increasing worldwide temperatures, raising sea levels and damaging agricultural yields.
According to the World Health Organization, air pollution accounts for as many as seven million premature deaths worldwide each year. This includes not only outdoor air pollution from vehicles, industrial sources and power generation, but also indoor air pollution from burning fuel for cooking or heat. Most of these deaths occur in the developing world, in countries where environmental regulations are less strict and the populations lack access to cleaner energy options.
Another way in which air pollution can be dangerous is when it contains particulates and volatile organic compounds. These particles can represent threats in many different ways, ranging from chemical effects on the body to low-level radiation, depending on the source. Breathing in these particles in smog can pose a significant health risk even beyond a respiratory problem. The nitric oxide and sulfur dioxide created when fossil fuels combust can also contribute to smog and acid rain.