The harmful pollutants released into the air by coal-fired electricity generation, such as sulphur, also dampen the greenhouse effect.

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We're conserving it - by taking off any harmful pollutants.

BBC: Rebecca Fountain in Bath

Harmful air pollutants in the United States, he adds, have fallen by 70 percent in the last two decades.

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But apples contain high levels of an antioxidant flavonoid called quercetin which is also found abundantly in onions, tea and red wine, and may be important in protecting the lungs from the harmful effects of atmospheric pollutants and cigarette smoke.

BBC: Apples 'protect the lungs'