Air pollution is a broad term applied to all physical (particulate matter), chemical, and biological agents that modify the natural characteristics of the atmosphere.
Some definitions also consider physical perturbations such as noise pollution, heat, radiation or light pollution as air pollution. Definitions commonly include the term harmful as a requisite to consider a change to the atmosphere as pollution.
Air Pollutants are classified as either Primary or Secondary. A primary air pollutant is one that is emitted directly to the air from a given source. Carbon monoxide is an example of a primary air pollutant because it is produced as a byproduct of combustion.
A secondary air pollutant is formed in the atmosphere through chemical reactions involving primary air pollutants. The formation of ozone in photochemical smog is an example of a secondary air pollutant.
DEATHS: It is estimated that three million people may die of air pollution each year worldwide. 2.8 million of the 3 million mortalities may be due to indoor air pollution. 90% of the 3 million estimated deaths are in developing nations. 70,000 die each year in the U.S. (Some estimates are as low as 50,000 or as high as 100,000). Deaths from air pollution are compared to deaths from second hand smoke and chemical weapons. In the U.S, more people die from air pollution than from car accidents. They die specifically from agitated asthma, bronchitis, emphysema, lung and heart diseases, and other respiratory allergies. The EPA estimates that a proposed set of changes in diesel fuel technology (Tier 2) could result in 12,000 fewer premature mortalities, 15,000 fewer heart attacks, 6,000 fewer emergency room visits by children with asthma, and 8,900 fewer respiratory-related hospital admissions each year in the US.
The worst short-term civilian event from pollution in India was the 1984 Bhopal Disaster. Leaked industrial vapors killed more than 2,000 people outright and injured anywhere from 150,000 to 600,000 others, some 6,000 of whom would later die from their injuries. The worst single incident of air pollution to occur in the United States of America occurred in Donora, Pennsylvania in late October, 1948, when 20 people died and over 7,000 were injured. The United Kingdom suffered its worst air pollution event when the December 4th Great Smog of 1952 formed over London. In six days more than 4,000 died, and 8,000 more died within the following months. An accidental leak of anthrax spores from a biological warfare laboratory in the former USSR in 1979 near Sverdlovsk is believed to have been the cause of hundreds of civilian deaths.
Intentional air pollution in combat is called chemical warfare. Poison gas as a chemical weapon was principally used during World War I, and resulted in an estimated 91,198 deaths and 1,205,655 injuries. Various treaties have sought to ban its further use. Non-lethal chemical weapons, such as tear gas and pepper spray, are widely used.
POLLUTION SOURCES: Anthropogenic Sources related to burning different kinds of fuel - human activity
· Combustion-fired power plants.
· Vehicles with internal combustion engines.
· Devices powered by Two-stroke cycle engines.
· Stoves and incinerators, especially coal ones.
· Wood fires, which usually burn inefficiently.
· Farmers burning their crop waste.
Other Anthropogenic Sources
· Aerosol sprays and refrigeration, which once depended on Freon and other chlorofluorocarbons.
· Arsenic and chlorine found in drinking water and inhaled in bathroom showers.
· Dust and chemicals from farming, especially of erodible land, see Dust Bowl.
· Fumes from paint, varnish, and other solvents.
· Industrial activity in general.
· Military actions, including the use and testing of nuclear bombs, poison gases, and germ warfare.
· Oil refining.
· Rocketry, which produces many tons of exotic emissions quickly and which deposits some of them directly into the tenuous upper atmosphere.
· Waste deposition in landfills, which generate methane.
· Dust from natural sources, usually large areas of land with little or no vegetation.
· Methane, emitted by the digestion of animals, usually cattle.
· Pine trees, which emit volatile organic compounds (VOCs) and oxygen.
· Radon gas from earth minerals.
· Smoke and carbon monoxide from wildfires.
· Volcanic activity, which produce sulfur, chlorine, and ash particulates.
CONTAMINANTS: Contaminants of air can be divided in particulates and gases.
Particulates are small, solid particles, classified by their sizes. Atmospheric particles are usually measured as TSP, PM10 or PM2.5. TSP stands for Total Suspended Particulates. The PM10 fraction consists of particles with an aerodynamic diameter of less than 10 micrometres; these are more dangerous to humans than TSP, because they can be breathed deep into the respiratory tract and reach the lungs. PM2.5 particles are even more dangerous because they can pass through the upper airway filtering and into the alveoli, where they can cross the lung/blood stream barrier and transport into the blood. Increasing attention is now focusing on the health impacts of even smaller particles- the so-called 'nanoparticles'. Smaller particles tend to be more toxic than larger particles and can stay airborne as an 'aerosol' for longer than larger particles, which settle out more quickly.
Important pollutant gases include:
· Carbon monoxide, which is primarily emitted from combustion process, particularly from petrol vehicle exhausts due to incomplete combustion; the highest concentrations are generally found at roadside locations. Inhalation of high levels of carbon monoxide can cause headaches, fatigue and respiratory problems. According to the EPA (as presented in the 2002 World Almanac), 97,441 thousand short tons of carbon monoxide were released in the United States during the year 1999, 75,151 of those caused by transportation related exhaust.
· Chlorofluorocarbons, which destroy the stratospheric ozone layer.
· Lead and heavy Metals
· Nitrogen oxides, or NOx. Emissions are primarily in the form of NO, which is oxidised by ozone (O3) from nitric oxide to NO2. Nitrogen dioxide (NO2) is the primary concern for effects on health, and is the species for which WHO health-based standards are expressed. The various oxides of nitrogen can also react with hydrocarbons in the atmosphere to contribute to photochemical smog. NOx can also affect ecologically sensitive sites through deposition, causing acidification and eutrophication. In The U.S., 25,393 short tons of Nitrogen Oxide were released during 1999 .
· Sulfur oxides, which causes acid rain is caused from the burning of fuel containing sulfur, mostly at power plants, and during metal smelting and other industrial processes. In the U.S., 12.46 tons of sulfur dioxide were released in 1999 , however there has been a 33 percent decrease in emissions between 1983 and 2002, due largely to state restrictions.
· Tropospheric ozone, which is ozone in the lower part of the atmosphere. Ozone (O3) is a secondary pollutant, formed through photochemical reactions involving NOx and hydrocarbons; it is an irritant gas. In the stratosphere it helps to reduce the amount of ultraviolet radiation from the sun that reaches earth.
· Volatile organic compounds: gasoline, solvents, cleaning solutions.
CONTROL DEVICES: The following items are commonly used as pollution control devices by industry or transportation devices. They can either destroy contaminants or remove them from an exhaust stream before it is emitted to the atmosphere.
· Electrostatic precipitator
· Air filter
· Cyclone (industry)
· Selective catalytic reduction
· Catalytic converter
· Flue gas desulfurization
· Exhaust gas recirculation
· Gas flare
INDOOR AIR POLLUTION: The lack of ventilation indoors concentrates air pollution where people are most exposed to them. Background pollution comes from such mundane sources as shower water mist containing arsenic or manganese, both of which are damaging to inhale. The arsenic can be trapped with a shower nozzle filter. Radon gas, a carcinogen, is exuded from the earth and trapped inside houses. Researchers have found that radon gas is responsible for over 1,800 deaths annually in the United Kingdom. These natural radon emissions can be blocked by a layer of aluminum foil under the carpet (according to the U.S. Department of Air Quality Management).
Building materials including carpeting and plywood emit formaldehyde gas. Paint and solvents give off volatile organic compounds (VOCs) as they dry. Lead paint can degenerate into dust and be inhaled. Asbestos insulation was commonly used in many application and can be carcinogenic in the lungs. Intentional air pollution is introduced with the use of air fresheners, incense, and other scented items. Controlled wood fires in stoves and fireplaces can add significant amounts of smoke particulates into the air, inside and out. Clothing emits perchloroethylene for days after dry cleaning.
Deaths are often caused by using pesticides and other chemical sprays indoors without proper ventilation, and many homes have been destroyed by accidental pesticide explosions. Second-hand tobacco smoke is now recognized as an indoor air pollutant which accounts for an estimated 3,000 lung cancer deaths annually in the US. Carbon monoxide poisoning is a quick and silent killer, often caused by faulty vents and chimneys, or by the burning charcoal indoors. 56,000 Americans died from CO in the period 1979-1988. Chronic carbon monoxide poisoning can result even from poorly adjusted pilot lights. Smoke inhalation is a common cause of death in victims of house fires. Traps are built into all domestic plumbing to keep deadly sewer gas, hydrogen sulfide, out of interiors.
Biological sources of air pollution can also be found indoors, and include gases, particulates, allergens, and microbes. Pets produce dander, bed mites deposit shells and microscopic droppings, inhabitants emit methane, mold can form in walls and generate spores, air conditioning systems can incubate Legionnaires disease, toilets can emit feces-tainted mists, and houseplants and surrounding gardens can produce pollen, dust, and mold spores.