how+do+human+activities+contribute+to+it+08


 * Carbon monoxide (CO) ** is produced by the incomplete burning of carbon-based fuels, including gasoline, oil, and wood. It is also produced from incomplete combustion of natural and synthetic products, such as cigarette smoke. It can build up in high concentrations in enclosed areas such as garages, poorly ventilated tunnels, and even along roadsides in heavy traffic.


 * Carbon dioxide (CO2) ** is the principal greenhouse gas emitted as a result of human activity (e.g. burning coal, oil, and natural gas).


 * Chlorofluorocarbons (CFCs) ** are chemicals used in great quantities in industry, for refrigeration and air conditioning, and in consumer products.


 * Hazardous air pollutants (HAPs) ** are released by sources such as chemical plants, dry cleaners, printing plants, and motor vehicles including cars, trucks, buses, planes.


 * Lead ** has been phased out of gasoline, which has considerably reduced the contamination of air by lead. However, lead can still be inhaled or ingested from other sources. The sources for lead include paint (for houses and cars), smelters, manufacture of lead batteries, fishing lures, certain parts of bullets, some ceramic ware, mini blinds, water pipes, and a few hair dye products.


 * Ozone (O3) ** is a gas that is a variety of oxygen. Ground-level ozone comes from the breakdown (oxidation) of volatile organic compounds found in solvents. It is also a product of reactions between chemicals that are produced by burning coal, gasoline, other fuels, and chemicals found in paints and hair sprays. Oxidation occurs readily during hot weather. Vehicles and industries are major sources of ground-level ozone.


 * Nitrogen oxides (NOx) ** are produced from burning fuels, including gasoline and coal. Aerosols of acids from NOx reduce visibility.


 * Particulate matter ** is produced by many sources, including burning of diesel fuels by trucks and buses, fossil fuels, mixing and application of fertilizers and pesticides, road construction, industrial processes such as steel making, mining, agricultural burning, and operation of fireplaces and woodstoves.

** Sulphur **** dioxide (SO2) ** is a gas produced by burning coal, most notably in power plants. Some industrial processes, such as production of paper and smelting of metals, produce sulphur dioxide.


 * Volatile organic compounds (VOCs) ** are released from burning fuel, such as gasoline, wood, coal, natural gas and from solvents, paints, glues, and other products used at home or work. Vehicle emissions are an important source of VOCs.

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