MARK CLARKE / SCIENCE PHOTO LIBRARY MARK CLARKE / SCIENCE PHOTO LIBRARY
Air pollution mask. Seven-year- old boy in a cycling helmet wears an anti- pollution mask. The mask over his mouth and nose is to protect him against the air pollution in a city street. The main source of air pollution in cities is from car exhausts. Cars produce poisonous gases such as nitrogen oxides, sulphur oxides, carbon monoxide and ozone. They also emit unburnt hydrocarbons, lead fumes and partially burnt, microscopic particles of soot. Face masks like the one shown here may filter out the larger particles of soot but may not provide sufficient protection against the other pollutants.
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