INTRODUCTION The composition of unpolluted air is unknown unknown to us. Humans have lived lived on the planet thousands of years and influenced the composition of the air through their many activities before it was possible to measure the constituents of the air. Air is a complex mixture made up of many chemical components. The primary components of air are nitrogen (N2), oxygen (O2), and water water vapor (H2O). About 99 percent percent of air, is nitrogen (78%) and oxygen (21%). The remaining remaining 1 percent includes trace quantities of substances substances such such as carbon dioxide (CO2), methane (CH4), hydrogen (H2), argon (Ar) and helium (He). In theory, the air has always been polluted to some degree. Natural phenomena such as volcanoes, wind storms, the decomposition of plants and animals, and even the aerosols emitted by the ocean "pollute" the air. However, the pollutants we usually refer to when we talk about air pollution are those generated as a result of human activity. An air pollutant can be considered as a substance in the air that, in high enough concentrations, produces a detrimental environmental effect. These effects can be either health effects or welfare effects. A pollutant can affect the health of humans, as well as the health of plants and animals. Pollutants can also affect non-living materials such as paints, metals, and fabrics. An environmental effect is defined as a measurable or perceivable detrimental change resulting from contact with an air pollutant. Human activities have had a detrimental effect on the makeup of air. Activities such as driving cars and trucks, burning of coal, oil and other fossil fuels, and manufacturing chemicals have changed the composition of air by introducing many pollutants. There are hundreds of pollutants in the ambient air. Ambient air is the air to which the general public has access, i.e. any unconfined portion of the atmosphere. The two basic physical forms of air pollutants are particulate matter and gases. Particulate matter includes small solid and liquid particles such as dust, smoke, sand, pollen, mist, and fly ash. Gases include substances such as carbon monoxide (CO), sulfur dioxide (SO2), nitrogen oxides (NO2), and volatile organic compounds. Pollutants can also be classified as either primary pollutants or secondary pollutants. A primary pollutant is one that is emitted into the atmosphere directly from the source of the pollutant and retains the same chemical form. An example of a primary pollutant is the ash produced by the burning of solid waste. A secondary pollutant is one that is formed by atmospheric reactions of precursor or primary emissions. Secondary pollutants undergo a chemical change once they reach the atmosphere. An example of a secondary pollutant is ozone created from organic vapors given off at a gasoline station. The organic vapors react with sunlight in the atmosphere to produce the ozone, the primary component of smog. Control of secondary pollutants is generally more problematic than that of primary pollutants, because mitigation of secondary pollutants requires the identification of the precursor compounds and their sources as well as an understanding of the specific chemical reactions that result in the formation of the secondary pollutants.
The Environmental Protection Agency (EPA) has further classified ambient air pollutants for regulatory purposes as hazardous air pollutants (HAPs) and criteria pollutants. Criteria pollutants are pollutants that have been identified as being both common and detrimental to human welfare and are found over all the United States (ubiquitous pollutants). EPA currently designates six pollutants as criteria pollutants. These criteria pollutants are: carbon monoxide (CO), sulfur oxides (SOx), nitrogen oxides (NOx), ozone (O3), lead (Pb), and particulate matter (PM). On the other hand, EPA refers to chemicals that cause serious health and environmental hazards as hazardous air pollutants (HAPs) or air toxics. Hazardous air pollutants are those pollutants that are known or suspected to cause cancer or other serious health effects, such as reproductive effects or birth defects, or adverse environmental effects. Units 5 and 6 of this module discuss in more details the criteria pollutants and the hazardous air pollutants. The air we breathe An active person inhales 10,000-20,000 litres of air each day - about 7-14 litres per minute, although a person taking strenuous physical exercise (e.g. jogging) may inhale up to 50 litres of air per minute. A 3 year old child at rest inhales twice as much air per unit body weight than an adult; thus as their airways are narrower, and their lungs still developing, problems as a result of breathing in pollutants are likely to be more serious and longer lasting. Air composition
Air is a mixture of gases in the lower atmosphere. Dry air at sea level is composed in volume of nitrogen (78.08%), oxygen (20.95%), argon (0.93%), carbon dioxide (0.03%), together with very small amounts of other gases. Water vapour is found in variable concentrations.
The Environmental Protection Agency (EPA) has further classified ambient air pollutants for regulatory purposes as hazardous air pollutants (HAPs) and criteria pollutants. Criteria pollutants are pollutants that have been identified as being both common and detrimental to human welfare and are found over all the United States (ubiquitous pollutants). EPA currently designates six pollutants as criteria pollutants. These criteria pollutants are: carbon monoxide (CO), sulfur oxides (SOx), nitrogen oxides (NOx), ozone (O3), lead (Pb), and particulate matter (PM). On the other hand, EPA refers to chemicals that cause serious health and environmental hazards as hazardous air pollutants (HAPs) or air toxics. Hazardous air pollutants are those pollutants that are known or suspected to cause cancer or other serious health effects, such as reproductive effects or birth defects, or adverse environmental effects. Units 5 and 6 of this module discuss in more details the criteria pollutants and the hazardous air pollutants. The air we breathe An active person inhales 10,000-20,000 litres of air each day - about 7-14 litres per minute, although a person taking strenuous physical exercise (e.g. jogging) may inhale up to 50 litres of air per minute. A 3 year old child at rest inhales twice as much air per unit body weight than an adult; thus as their airways are narrower, and their lungs still developing, problems as a result of breathing in pollutants are likely to be more serious and longer lasting. Air composition
Air is a mixture of gases in the lower atmosphere. Dry air at sea level is composed in volume of nitrogen (78.08%), oxygen (20.95%), argon (0.93%), carbon dioxide (0.03%), together with very small amounts of other gases. Water vapour is found in variable concentrations.
SOURCE OF AIR POLLUTION Power Generation
Siting fossil fuel power stations in mainly rural areas and distributing the pollution produced more evenly via tall chimneys has resulted in improved urban air quality, though they still remain a major source of pollution, mainly sulphur dioxide and nitrogen oxides. Better dispersion of pollutants emitted by tall chimneys leads to better dilution in the air and thus lower local concentrations of pollutants. This has however led to pollution being dispersed more widely and to transboundary air pollution. Stricter operating practices and the use of modern abatement techniques have resulted in a considerable reduction in the amount of pollutants emitted from power stations; high concentrations do however occur in many eastern European countries, particularly from older power stations and from the use of high sulphur lignite or brown coal. Exceptional concentrations may also occur on a very local basis if a plume of smoke from, for example, an industrial chimney falls to the ground due to local atmospheric conditions. conditions. The countries of the European Union and those which are a party to the UNECE Convention on the Long Range Transport of Air Pollution, Second Sulphur Protocol, are committed to major reductions in sulphur dioxide emissions. Power generation is, however, likely to remain an important source of pollution for some time to come, particularly as some countries are reconsidering their programmes of nuclear power generation.
Other Industry and waste disposal
Although fossil fuel power plants are the major source of industrial air pollution in many countries, all industry and many businesses, large and small, can be significant local sources of a wide range of air pollutants. The use of both regulatory and planning controls will help to minimise their effect on local air quality. All waste has the potential to affect the environment adversely by contaminating the air, soil or water. Poorly managed waste disposal sites (landfill or incineration) can also pose a danger to public health, through all these routes. Landfill and incineration are the two most common methods of waste disposal. If not properly managed landfill sites can cause a number of problems; these include the production of potentially explosive levels of methane gas (65%), dangerous levels of carbon dioxide (35%), plus trace concentrations of a range of organic gases and vapours. Landfill sites also have the potential to cause major odour when badly managed. Uncontrolled or poorly managed burning of waste (incineration) can result in the production of poisonous chemicals such as hydrochloric acid, dioxins, furans and heavy metals. Hydrochloric acid contributes locally to acid rain and is given off by the burning of plastics. If organic matter and plastics are burnt at low temperatures, dioxins and furans may be emitted. Modern, properly operated incinerators produce fumes which respect the strictest existing legislation. Road Transport
Air pollution from motor vehicles has, in many countries, replaced coal smoke as the major cause for concern; and the continuing growth in vehicle use means that efforts to reduce emissions from individual vehicles are in danger of being overtaken by increases in the volume of traffic. In much of eastern Europe the continued use of rather old cars, which are unable to meet modern pollution control requirements, means that efforts to control pollution from this source are going to be increasingly difficult. The air pollutants produced as a result of the use of motor vehicles present a two-stage problem: primary and secondary pollutants. Primary pollutants produced by petrolpowered vehicles include carbon monoxide, nitric oxide, benzene, particulate matter and lead. Much of the lead emitted by vehicles burning leaded petrol emerges as particles. Diesel engines burn fuel in excess of air and so produce little carbon monoxide but, instead large quantities of carbon dioxide, (see table). Secondary pollutants produced as a result of the use of petrol-engined vehicles include nitrogen dioxide and ozone. MEASURES TO REDUCE AUTOMOBILE CONTRIBUTION TO POLLUTION
Measures for inclusion in a Local Transport Strategy • • •
•
•
•
•
Adequate and affordable public transport; Provision of safe cycling and pedestrian routes; Regular emissions testing of private and public transport vehicles; Encouraging local business to use car pooling or car sharing schemes; Encouraging less use of motor cars during weather conditions likely to lead to an episode of pollution. Encouraging better fuel quality Better planning of the built environment aimed at reduced mobility and improved access to shops, jobs, etc.
In those countries which have required the removal of lead from petrol, concentrations of lead in air from this source have been reduced to a level at which they are no longer a problem. Lead-free petrol has also made the use of "catalytic converters" possible. Catalysts substantially reduce emissions of hydrocarbons, NOx and carbon monoxide; they do however increase emissions of carbon dioxide, an important greenhouse gas, and
have no effect on emissions of particles. Since 1993 all new petrol-engined cars in the European Union have to be fitted with catalytic converters. Prior to the introduction of cars fitted with catalytic converters, diesel-powered vehicles were considered "cleaner" than petrol-powered cars. EU legislation requires that they meet the same limits for hydrocarbons, NOx and CO as petrol-driven cars. Diesel fuel contains no lead but is a considerable source of particulate matter, PAHs and SO2. The introduction of lower sulphur diesel fuels throughout the EU will reduce emissions from this source In many countries, there has been a policy of progressively tightening emission standards for cars and lorries in line with EU directives and UNECE standards. However, much more will need to be done to ensure that reductions in vehicle emissions are not offset by the rapid increase in vehicle ownership and use. This is an area in which action by local authorities can make a significant impact on local air quality and indeed benefit the local community in terms both of their health and of local amenities. Each local authority will need to consider how it can best tackle the problem, bearing in mind the resources available and other priorities for cutting pollution. Improved public transport, park and ride schemes, traffic restrictions, planning guidelines and encouragement to cycle and walk are some of the measures that local authorities can take. Requiring vehicle owners to maintain their vehicles regularly will ensure that fuel is burnt efficiently and economically, and will therefore be less polluting; and fuel consumption is more efficient at lower speeds (60 - 90 km/h).
Average emission factors of different fuels Emission factor
Environmental third class diesel
Environmental first class diesel
Ethanol
Regulated pollutants: Carbon monoxide, g/km
3.3
1.9
0.25
Hydrocarbons, g/km
1.3
0.72
0.13
NOX, g/km
13.2
9.7
9.5
Particulates, mg/km
510
200
53
Carbon dioxide, kg/km
1.2
1.1
1.2
Formaldehyde, mg/km
70
29
18
Unregulated pollutants:
Acetaldehyde, mg/km
19
20
72
220
39
6.0
Sum, particle-bound PAH (> 3 aromatic rings) mg/km
Domestic Sources
Before about 1960, the domestic use of coal was the major source of particles. Concentrations of airborne particles in many European cities frequently exceeded 1000 µg/m3 and annual average concentrations of several hundred µg/m3 were commonplace. Today, annual average concentrations in most European cities have fallen to less than 30 µg/m3. In eastern Europe much higher concentrations still occur as, to a lesser extent, they do in southern European cities such as Athens. Brown coal (lignite) is a key source of particles in many parts of eastern Europe. Coal varies in composition and calorific value from mine to mine. Lignite is probably the poorest quality in terms of calorific value and generates most pollutants when used for domestic heating. Lignite contains 67% carbon (compared with the 95% in anthracite, which is another type of coal) and burns easily, though inefficiently, on an open fire. Special devices with carefully controlled air supplies are needed to burn anthracite but combustion is efficient and far less black smoke is produced. Conversion of open fires to stoves suitable for burning anthracite (or other smokeless fuel) should be considered by any local authority where coal smoke is a problem. The greater efficiency of controlled anthracite burning leads to a saving in overall fuel costs, though an initial investment in the necessary equipment must be made. Conversion to stoves which ensure complete combustion are also a possibility as are district heating schemes, using combined heat and power plants. The greater use of renewable energy
(wind, solar, tidal, wave, etc.) and enhanced energy efficiency measures in homes and offices also helps improve air quality. Other important domestic sources of air pollution are: •
•
Gas and paraffin heaters, stoves and cookers produce carbon monoxide. If ventilation is inadequate or appliances poorly maintained, CO may accumulate in dangerous concentrations. Nitrogen dioxide is also generated and concentrations in kitchens will usually exceed those outdoors when cookers are in use. Ventilators can help reduce this pollution; Bonfires, garden incinerators and barbecues can be a significant local smoke and odour nuisance. Burning garden waste produces smoke, especially if it is damp and smouldering rather than dry and blazing. The smoke contains CO and other noxious and irritating compounds. Problems may be caused for asthmatics, bronchitis sufferers or those with heart conditions. Even if the immediate health risk is small, bonfires add to the general background level of air pollution.
Agriculture
Agricultural practices can also be a significant source of nuisance, contributing both to local levels of air pollution and causing odour problems. The main sources of pollution are the burning of agricultural waste, or of crops in the field and large intensive livestock units. Depending on soil type and fertilisation, the nitrogen in the dung and urine of grazing cattle contributes 20-40% of nitrous oxide emissions from agricultural land; methane is also emitted by cattle and other ruminants; nitrous oxide and methane are of course both greenhouse gases.
ELEMENTS OF AIR POLLUTION The Great Smog of 1952 Early in December 1952, a cold fog descended upon London. Because of the cold, Londoners began to burn more coal than usual. The resulting air pollution was trapped by the inversion layer formed by the dense mass of cold air. Concentrations of pollutants, coal smoke in particular, built up dramatically. The problem was made worse by use of low-quality, high-sulphur coal for home heating in London in order to permit export of higher-quality coal, because of the country's tenuous postwar economic situation. The "fog", or smog, was so thick that driving became difficult or impossible. The extreme reduction in visibility was accompanied by an increase in criminal activity as well as transportation delays and a virtual shut down of the city. During the 4 day period of fog, at least 4,000 people died as a direct result of the weather. INDOOR AIR QUALTIY Indoor air quality (IAQ) is a term referring to the stuff within and around buildings and structures, especially as it relates to the health and comfort of building occupants. IAQ can be affected by microbial contaminants (mold, bacteria), gases (including carbon monoxide, radon, volatile organic compounds), particulates, or any mass or energy stressor that can induce adverse health conditions. Indoor air is becoming an increasingly more concerning health hazard than outdoor air. Using ventilation to dilute contaminants, filtration, and source control are the primary methods for improving indoor air quality in most buildings. Determination of IAQ involves the collection of air samples, monitoring human exposure to pollutants, collection of samples on building surfaces and computer modelling of air flow inside buildings.
Carbon Dioxide (CO2) Air pollution and global warming, as most scientists agree, seem to go hand in hand. The main component of this is the greenhouse gas, carbon dioxide. Carbon Dioxide is a necessary gas for our survival. They call it a greenhouse gas because it makes the Earth habitable by blocking some of the sun's radiation from exiting the atmosphere. Without carbon dioxide, the whole planet would be covered in ice. Just like anything else in life, too much of a good thing can be a problem and that is what scientists have been warning us for years. Carbon dioxide levels have now risen to 31% of pre-industrial revolution
days and the gas emitted from 100-200 years ago may still be in our atmosphere today. A constant warming cycle can start melting polar ice caps and cause flooding. Ozone (O3) Ozone is the primary ingredient in smog and forms when hydrocarbons and nitrous oxides react with sunlight. Not all ozone is bad, in fact, like carbon dioxide, it is quite beneficial in the upper atmosphere as it keeps harmful ultra-violet light out, a major cause of skin cancer. It becomes a problem when it hovers in the lower atmosphere where it can enter the lungs. Ozone inhalation can produce coughing, choking, and reduced lung capacity. It can also worsen chronic respiratory diseases such as asthma and compromise the body's ability to fight off respiratory infections. Recovery from short-term exposure to ozone can occur, but longer exposure may make recovery less certain. Although ozone is not directly related to anything we may use, it does form when nitrous oxides and volatile organic compounds react with sunlight. Nitrogen Oxide (Nox)
Nitrogen oxides form when fuels are burned at high temperatures. Your car and power plants that burn coal, oil, and natural gas are the major producers. These pollutants can cause lung irritation and inhibit the body's ability to fight off diseases such as influenza and pneumonia. They also help to form ozone and particulate matter. Nitrogen dioxide is decomposed by sunlight into nitrogen monoxide and atomic oxygen, which in-turn combines immediately with oxygen to form ozone (03). The more sunlight available, the faster the reaction goes. Therefore, during summer in areas with high traffic, concentrations will increase. Carbon Monoxide (CO) An odorless, colorless gas, inhalation of carbon monoxide blocks the blood's ability to carry oxygen. Due to its chemical structure, it can easily attach to hemoglobin, the oxygen carrying pigment in red blood cells. With CO in our bodies, our organs are essentially poisoned as oxygen fails to reach them. Higher levels of poisoning result in dizziness, mental confusion, severe headaches, nausea, and fainting on mild exertion. Particulate Matters Miniscule pieces of soot, pollen, and metals are what give smog a cloudy color. The smaller the pieces of soot, the more damaging they can be. These particles can penetrate deep into the lungs and eventually be absorbed into the bloodstream where they can remain for long periods of time. Exposure to particulate matter can cause asthma attacks, wheezing, and coughing. Research has also shown that exposure to low concentrations of
particulate matter can lead to premature death with the elderly and people with preexisting heart disease at greatest risk. Sulphur Oxide (SO3) A by-product of burning diesel gas, sulfur dioxide can adversely affect young children and asthmatics. The sulfur dioxide content in the air is directly proportional to the sulfur content in the fuel. The gas is a colorless, toxic gas that gives off a characteristic bad odor. The oxidation of sulfur dioxide turns into sulfur trioxide, which is a starting point for sulfuric acid, the major component of acid rain. Hazardous Pollutants Also known as toxic air pollutants or air toxics are pollutants that can cause cancer and other serious health effects such as birth defects. An example of an air pollutant found in gasoline is benzene, toluene, and xylenes. Volatile Organic Chemicals (VOC) VOC's have properties of being a gas at room temperatures. Often 10 times higher concentrations indoors than outdoors, these air pollutants can have short and long term effects. These products all contain VOC's: • • • • • • • • • •
Paints Lacquers Paint strippers Cleaning supplies Pesticides Building materials Office equipment Glues and adhesives Permanent markers Photographic solutions
Many of the cleaning agents also contain organic solvents. Eye, nose, and mouth irritation, headaches, dizziness, fatigue, allergic skin reactions can all be symptoms of inhalation of these chemicals. If you do use these chemicals, make sure there is plenty of ventilation and put the caps back on tight when done. Gas can still leak out of the containers after closing them so if you have old chemicals and don't use them, then discard them properly. Paint strippers, adhesive removers, and aerosol spray paints all contain the solvent methylene chloride, which the body can convert to carbon monoxide, so use extreme care when using these chemicals.
Benzene C6H6 Benzene is a known human carcinogen, so keep exposure to that at a minimum. Benzene is found in tobacco smoke, stored fuels, and paint supplies. Discard paint supplies and fuels that are not used. Formaldehyde CH20 Did you just have new carpet installed in your home or just finished an insulation project? If the answer is yes, then formaldehyde gas may be leaking from them. A major source of formaldehyde is building materials. Carpets, insulation foam, and particleboard all contain formaldehyde. Mobile homes and new homes with pressed-wood materials can contain significant amounts of formaldehyde. Headaches, dizziness, nausea, and other eye, respiratory, and skin irritations are all common symptoms. Environmental experts disagree as to what is a safe limit of formaldehyde for the general public. Radon Indoor radon is the second leading cause of lung cancer in the United States and the leading cause among non-smokers. Radon is a colorless, odorless, and tasteless natural radioactive gas released from the earth. This air pollutant enters the environment through the soil, through uranium and phosphate mines, and through coal combustion. Because it is a heavy gas, it tends to collect in basements, entering through spaces in the soil or fill material around a home's foundation. Detectors are available that will measure the amount of radon in your home. Perchloroethylene This chemical is used most widely in dry cleaning. When your clothes come back from the dry cleaners, make sure there is no chemical smell emanating from them. If you do smell something, do not accept them until they have dried completely. At higher concentrations, perchloroethylene can range from dizziness and headaches to excessive sweating and unconsciousness.
HEALTH EFFECTS The World Health Organization states that 2.4 million people die each year from causes directly attributable to air pollution, with 1.5 million of these deaths attributable to indoor air pollution. "Epidemiological studies suggest that more than 500,000 Americans die each year from cardiopulmonary disease linked to breathing fine particle air pollution . A study by the University of Birmingham has shown a strong correlation between pneumonia related
deaths and air pollution from motor vehicles. Worldwide more deaths per year are linked to air pollution than to automobile accidents. Published in 2005 suggests that 310,000 Europeans die from air pollution annually. Direct causes of air pollution related deaths include aggravated asthma, bronchitis, emphysema, lung and heart diseases, and respiratory allergies. The US EPA estimates that a proposed set of changes in diesel engine 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 United States
The worst short term civilian pollution crisis in India was the 1984 Bhopal Disaster . Leaked industrial vapors from the Union Carbide factory, belonging to Union Carbide, Inc., U.S.A., 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 United Kingdom suffered its worst air pollution event when the December 4 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. 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 health effects caused by air pollutants may range from subtle biochemical and physiological changes to difficulty in breathing, wheezing, coughing and aggravation of existing respiratory and cardiac conditions. These effects can result in increased medication use, increased doctor or emergency room visits, more hospital admissions and premature death. The human health effects of poor air quality are far reaching, but principally affect the body's respiratory system and the cardiovascular system. Individual reactions to air pollutants depend on the type of pollutant a person is exposed to, the degree of exposure, the individual's health status and genetics. A new economic study of the health impacts and associated costs of air pollution in the Los Angeles Basin and San Joaquin Valley of Southern California shows that more than 3800 people die prematurely (approximately 14 years earlier than normal) each year because air pollution levels violate federal standards. The number of annual premature deaths is considerably higher than the fatalities related to auto collisions in the same area, which average fewer than 2,000 per year. Diesel exhaust (DE) is a major contributor to combustion derived particulate matter air pollution. In several human experimental studies, using a well validated exposure chamber setup, DE has been linked to acute vascular dysfunction and increased thrombus
formation. This serves as a plausible mechanistic link between the previously described association between particulate matter air pollution and increased cardiovascular morbidity and mortality. Effects on cystic fibrosis A study from 1999 to 2000 by the University of Washington showed that patients near and around particulate matter air pollution had an increased risk of pulmonary exacerbations and decrease in lung function. Patients were examined before the study for amounts of specific pollutants like Pseudomonas aeruginosa or Burkholderia cenocepacia as well as their socioeconomic standing. Participants involved in the study were located in the United States in close proximity to an Environmental Protection Agency.During the time of the study 117 deaths were associated with air pollution. A trend was noticed that patients living closer or in large metropolitan areas to be close to medical help also had higher level of pollutants found in their system because of more emissions in larger cities. With cystic fibrosis patients already being born with decreased lung function everyday pollutants such as smoke emissions from automobiles, tobacco smoke and improper use of indoor heating devices could add to the disintegration of lung function. Effects of COPD Chronic Obstructive Pulmonary Disease (COPD ) - is also known as chronic obstructive lung disease and encompasses two major disorders: emphysema and chronic bronchitis. Emphysema is a chronic disorder in which the walls and elasticity of the alveoli are damaged. Chronic bronchitis is characterized by inflammation of the cells lining the inside of bronchi, which increases the risk of infection and obstructs airflow in and out of the lung. Smoking is responsible for approximately 80% of COPD cases while other forms of air pollution may also influence the development of these diseases. Symptoms include cough, production of mucous and shortness of breath. It is important to note that no cure exists for people suffering from COPD although healthy lifestyle and appropriate medication can help. A study conducted in 1960-1961 in the wake of the Great Smog of 1952 compared 293 London residents with 477 residents of Gloucester, Peterborough, and Norwich, three towns with low reported death rates from chronic bronchitis. All subjects were male postal truck drivers aged 40 to 59. Compared to the subjects from the outlying towns, the London subjects exhibited more severe respiratory symptoms (including cough, phlegm, and dyspnea), reduced lung function and increased sputum production and purulence. The differences were more pronounced for subjects aged 50 to 59. The study controlled for age and smoking habits, so concluded that air pollution was the most likely cause of the observed differences.
It is believed that much like cystic fibrosis, by living in a more urban environment serious health hazards become more apparent. Studies have shown that in urban areas patients suffer mucus hypersecretion, lower levels of lung function, and more self diagnosis of chronic bronchitis and emphysema. Effects on Children Cities around the world with high exposure to air pollutants have the possibility of children living within them to develop asthma, pneumonia and other lower respiratory infections as well as a low initial birth rate. Protective measures to ensure the youths' health are being taken in cities such as New Delhi, India where buses now use compressed natural gas to help eliminate the pea-soup smog. Research by the World Health Organization shows there is the greatest concentration of particulate matter particles in countries with low economic world power and high poverty and population rates. Examples of these countries include Egypt, Sudan, Mongolia, and Indonesia. The Clean Air Act was passed in 1970, however in 2002 at least 146 million Americans were living in areas that did not meet at least one of the “criteria pollutants” laid out in the 1997 National Ambient Air Quality Standards. Those pollutants included: ozone, particulate matter, sulfur dioxide, nitrogen dioxide, carbon monoxide, and lead. Because children are outdoors more and have higher minute ventilation they are more susceptible to the dangers of air pollution. Effects on Relatively Clean Areas Even in areas with relatively low levels of air pollution, public health effects can be substantial and costly. This is because effects can occur at very low levels and a large number of people can potentially breathe in such pollutants. A 2005 scientific study for the British Columbia Lung Association showed that a 1% improvement in ambient PM2.5 and ozone concentrations will produce a $29 million in annual savings in the region in 2010. This finding is based on health valuation of lethal (mortality) and sublethal (morbidity) effects. In the news, we hear about air pollution and its effect on a global scale. With our growing population becoming ever the more reliant on automobiles, chemicals, and other potentially hazardous substances, air pollutants can cause major health problems to your health. Some obvious causes of air pollution would be your car, but there are many not so obvious products that you may use everyday that are potentially damaging to your health. Human Respiratory Problems The health of our lungs and entire respiratory system is affected by the quality of the air we breathe. In addition to oxygen, this air contains other substances such as pollutants, which can be harmful. Exposure to chemicals by inhalation can negatively affect our
lungs and other organs in the body. The respiratory system is particularly sensitive to air pollutants because much of it is made up of exposed membrane. Lungs are anatomically structured to bring large quantities of air (on average, 400 million litres in a lifetime) into intimate contact with the blood system, to facilitate the delivery of oxygen. Lung tissue cells can be injured directly by air pollutants such as ozone, metals and free radicals. Ozone can damage the alveoli -- the individual air sacs in the lung where oxygen and carbon dioxide are exchanged. More specifically, airway tissues which are rich in bioactivation enzymes can transform organic pollutants into reactive metabolites and cause secondary lung injury. Lung tissue has an abundant blood supply that can carry toxic substances and their metabolites to distant organs. In response to toxic insult, lung cells also release a variety of potent chemical mediators that may critically affect the function of other organs such as those of the cardiovascular system. This response may also cause lung inflammation and impair lung function. Heart and lung illnesses and diseases are common in Canada, and there are many factors that can increase the chances of contracting them such as smoking and genetic predisposition. The role of air pollution as the underlying cause remains unclear but is the subject of considerable research. However, it is clear that air pollution, infections and allergies can exacerbate these conditions. An early diagnosis can lead to appropriate treatment and ensure a normal or close to normal quality of life. In many cases however, there is no cure and those affected may die prematurely. The following are the most prevalent diseases: Minor Lung Illnesses - the common cold is the most familiar of these, with symptoms including sore throat, stuffy or runny nose, coughing and sometimes irritation of the eyes. Lung Infections - croup, bronchitis, and pneumonia are caused by viruses or bacteria and are very common. Symptoms may include cough, fever, chills and shortness of breath. Asthma - is an increasingly common chronic disease among children and adults. It causes shortness of breath, coughing or wheezing or whistling in the chest. Asthma attacks can be triggered by a variety of factors including exercise, infection, pollen, allergies and stress. It can also be triggered by a sensitivity to non-allergic types of pollutants present in the air such as smog. Lung Cancer - is the most common cause of death due to cancer in women and men. Cigarette smoke contains various carcinogens and is responsible for most cases of this often fatal disease. The symptoms of lung cancer begin silently and then progress to chronic cough, wheezing and chest pain. Air pollution has been linked somewhat weakly to lung cancer.
Human Cardiac Problems Coronary Artery Disease - refers to the narrowing or blocking of the arteries or blood vessels that supply blood to the heart. This disease includes angina and heart attack which share similar symptoms of pain or pressure in the chest. Unlike angina, the symptoms caused by heart attack do not subside with rest and may cause permanent damage to the heart. Smoking, lack of exercise, excess weight, high cholesterol levels in the blood, family history and high blood pressure are some of the factors that may contribute to this disease. Heart Failure - is a condition in which the heart is unable to cope with its work load of pumping blood to the lungs and the rest of the body. The most common cause is severe coronary artery disease. The main symptoms are shortness of breath and swelling of the ankles and feet. Heart-Rhythm Problems - are irregular or abnormal rhythms of the heart beat. In some cases heart-rhythm problems are caused by coroneary artery disease. Symptoms of heart-rhythm problems influttering in the chest (palpitation) and feeling light-headed. Some heart-rhythm problems are life-threatening and need emergency treatment.
Pyramid of Health Effects
Air pollution can affect both the respiratory and cardiac systems. The health effects of air pollution can be seen as a pyramid, with the mildest but not common effects at the bottom of the pyramid, and the least common but more severe at the top of the pyramid. The pyramid demonstrates that as severity decreases the number of people affected increases. Respiratory-related symptoms such as chest discomfort, coughing and wheezing Population at Risk Although everyone is at risk from the health effects of air pollution, certain subpopulations are more susceptible. Individual reactions to air contaminants depend on several factors such as the type of pollutant, the degree of exposure and how much of the pollutant is present. Age and health are also important factors. The elderly and people suffering from cardio-respiratory problems such as asthma appear to be the most susceptible groups. Children and newborns are also sensitive to the health effects of air pollution since they take in more air than adults for their body weight and consequently, a higher level of pollutants. People who exercise outdoors on hot and smoggy days are also at greater risk due to their increased exposure to pollutants in the air.
Leading Causes of Hosptalisation
Respiratory and cardiovascular diseases are among the leading causes of hospitalization in Canada. In 1996-1997 there were 3.16 million hospital admissions in Canada of which cardiovascular and respiratory diseases accounted for 15% and 9%, respectively. Air pollution exacerbates the condition of people with respiratory and cardiovascular diseases and causes measurable increases in the rates of hospitalization for these diseases. We do not yet understand the role of air pollution in causing these illnesses in the Canadian population.
Leading Causes of Deaths
Cardiovascular and respiratory diseases are among the leading causes of death in Canada. In 1997, 37% and 9% of over 200 000 deaths were r elated to cardiovascular and respiratory diseases respectively.
Air pollution causes measurable increases in non-accidental mortality.
Diagramaitc Representation of the Vicious cylce of Air Pollution
Baseline gasoline composition and changes to composition
Combustion of gasoline in vehicles and subsequent changes in exhaust emissions
Changes in ambient air concentrations of pollutants
Changes in health effects
Changes in human exposure
Value of health benefits
Summary It helps to be aware of what is inside your household products and how they may be affecting your health. Environmentalists say to think globally but act locally, and the first step to following this mantra is knowledge. There are a multitude of other chemicals that contribute to air pollution. You may often use them day in and day out, perhaps even in your job. Take precaution when using them and always use them in a well-ventilated area. If you think you may have a serious problem in your home that doesn't involve an easy solution, such as radon, it would be wise to consult an environmental professional.
Most Polluted Cities around the world- A list. 1. Cairo 2. Delhi 3. Calcutta 4. Tianjin 5. Chongqing 6. Lucknow 7. Kanpur 8. Jakarta 9. Shenyang 10. Zhengzhou 11.Jinan 12. Lanzhou 13. Beijing 14. Taiyuan 15. Chengdu 16. Ahmadabad 17. Anshan 18.Wuhan 19. Bangkok 20. Nanchang
Dispersal of Air Pollutants Once in the environment, air pollutants may be dispersed via air, water, soil, living organisms and food. The pathways of dispersion vary greatly, depending upon both the emission source and the pollutant concerned. Rates and patterns of dispersion also depend to a large extent upon environmental conditions. Pollution dispersal in the air is affected by many factors: •
•
• •
meteorological conditions (especially wind speed, wind direction and atmospheric stability), the emission height (e.g. ground level sources such as road traffic or high level sources such as tall chimneys), local and regional geographical features, the source (e.g. fixed point, such as a chimney, or a diffuse number of sources such as cars and solvents).
During dispersion pollutants undergo a wide array of changes and transfers. Dilution occurs owing to mixing into the air. Separation or accumulation of pollutants occurs on the basis of physical characteristics of the pollutant. Chemical reactions occur, breaking down the original pollutant or converting it into new compounds. Some pollutants can also be removed from the transporting medium through deposition, for example, by settling out under the effects of gravity, by rainwash or by interception (scavenging) by plants and other obstructions. Many pollutants therefore show extremely complex dispersion patterns, especially in environments such as cities and towns where there are a large number of emission sources and major variations in environmental conditions. This complexity means that it is often very difficult to model or measure pollutant patterns and trends, and thus to predict levels of human exposure. Temporal variations in pollution levels are important. In many cases long-term trends exist, reflecting underlying changes in the rates of emission (e.g. as a result of technical or economic changes, or due to policy intervention). Superimposed upon these there may be annual variations, reflecting year-to-year differences in climate or source activity. Many pollutants also show marked seasonal, weekly and daily patterns, owing to cycles of activity and short-term climatic and other effects. Major, short-term pollution episodes may also occur as a result of sudden, accidental releases. Therefore measurements of exposure will vary according to when, where and for how long air monitoring is carried out. AIR POLLUTION LAWS IN INDIA 1948 – The Factories Act and Amendment in 1987 was the first to express concern for the working environment of the workers. The amendment of 1987 has sharpened its environmental focus and expanded its application to hazardous processes. 1981 - The Air (Prevention and Control of Pollution) Act provides for the control and abatement of air pollution. It entrusts the power of enforcing this act to the CPCB . 1982 - The Air (Prevention and Control of Pollution) Rules defines the procedures of the meetings of the Boards and the powers entrusted to them. 1982 - The Atomic Energy Act deals with the radioactive waste. 1987 - The Air (Prevention and Control of Pollution) Amendment Act empowers the central and state pollution control boards to meet with grave emergencies of air pollution. 1988 - The Motor Vehicles Act states that all hazardous waste is to be properly packaged, labelled, and transported.
GREENHOUSE GASSES Greenhouse gases are gases in an atmosphere that absorb and emit radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The main greenhouse gases in the Earth's atmosphere are water vapor , carbon dioxide, methane, nitrous oxide, and ozone. In our solar system, the atmospheres of Venus, Mars and Titan also contain gases that cause greenhouse effects. Greenhouse gases greatly affect the temperature of the Earth; without them, Earth's surface would be on average about 33 °C colder than at present. Human activities since the start of the industrial era around 1750 have increased the levels of greenhouse gases in the atmosphere. GREENHOUSE EFFECT ON EARTH”S ATMOSPHERE. In order, Earth's most abundant greenhouse gases are: • • • • • •
water vapor carbon dioxide methane nitrous oxide ozone chlorofluorocarbons
The contribution to the greenhouse effect by a gas is affected by both the characteristics of the gas and its abundance. For example, on a molecule-for-molecule basis methane is about eight times stronger greenhouse gas than carbon dioxide, but it is present in much smaller concentrations so that its total contribution is smaller. When these gases are ranked by their contribution to the greenhouse effect, the most important are. • • • •
water vapor, which contributes 36–72% carbon dioxide, which contributes 9–26% methane, which contributes 4–9% ozone, which contributes 3–7%
It is not possible to state that a certain gas causes an exact percentage of the greenhouse effect. This is because some of the gases absorb and emit radiation at the same frequencies as others, so that the total greenhouse effect is not simply the sum of the influence of each gas. The higher ends of the ranges quoted are for each gas alone; the lower ends account for overlaps with the other gases. The major non-gas contributor to the Earth's greenhouse effect, clouds, also absorb and emit infrared radiation and thus have an effect on radiative properties of the greenhouse gases.
In addition to the main greenhouse gases listed above, other greenhouse gases include sulfur hexafluoride, hydrofluorocarbons and perfluorocarbons. Some greenhouse gases are not often listed. For example, nitrogen trifluoride has a high global warming potential but is only present in very small quantities.
Atmospheric absorption and scattering at different electromagnetic wavelengths. The largest absorption band of carbon dioxide is in the infrared. Scientists who have elaborated on Arrhenius's theory of global warming are concerned that increasing concentrations of greenhouse gases in the atmosphere are causing an unprecedented rise in global temperatures, with potentially harmful consequences for the environment and human health. Although contributing to many other physical and chemical reactions, the major atmospheric constituents, nitrogen (N2), oxygen (O2), and argon (Ar), are not greenhouse gases. This is because molecules containing two atoms of the same element such as N2 and O2 and monatomic molecules such as Ar have no net change in their dipole moment when they vibrate and hence are almost totally unaffected by infrared light. Although molecules containing two atoms of different elements such as carbon monoxide (CO) or hydrogen chloride (HCl) absorb IR, these molecules are shortlived in the atmosphere owing to their reactivity and solubility. As a consequence they do not contribute significantly to the greenhouse effect and are not often included when discussing greenhouse gases. Late 19th century scientists experimentally discovered that N 2 and O2 did not absorb infrared radiation (called, at that time, "dark radiation") and that water as a vapour and in cloud form, CO2 and many other gases did absorb such radiation. It was recognized in the early 20th century that the greenhouse gases in the atmosphere caused the Earth's overall temperature to be higher than it would be without them. TYPES OF GREEHOUSE GASSES Since about 1750 human activity has increased the concentration of carbon dioxide and other greenhouse gases. Measured atmospheric concentrations of carbon dioxide are currently 100 ppmv higher than pre-industrial levels. Natural sources of carbon dioxide are more than 20 times greater than sources due to human activity, but over periods
longer than a few years natural sources are closely balanced by natural sinks such as weathering of continental rocks and photosynthesis of carbon compounds by plants and marine plankton. As a result of this balance, the atmospheric concentration of carbon dioxide remained between 260 and 280 parts per million for the 10,000 years between the end of the last glacial maximum and the start of the industrial era. It is likely that anthropogenic warming, such as that due to elevated greenhouse gas levels, has had a discernible influence on many physical and biological systems. Warming is projected to affect various issues such as freshwater resources, industry, food and health. The main sources of greenhouse gases due to human activity are: •
•
•
•
burning of fossil fuels and deforestation leading to higher carbon dioxide concentrations. Land use change (mainly deforestation in the tropics) account for up to one third of total anthropogenic CO2 emissions. livestock enteric fermentation and manure management, paddy rice farming, land use and wetland changes, pipeline losses, and covered vented landfill emissions leading to higher methane atmospheric concentrations. Many of the newer style fully vented septic systems that enhance and target the fermentation process also are sources of atmospheric methane. use of chlorofluorocarbons (CFCs) in refrigeration systems, and use of CFCs and halons in fire suppression systems and manufacturing processes. agricultural activities, including the use of fertilizers, that lead to higher nitrous oxide (N2O) concentrations.
The seven sources of CO 2 from fossil fuel combustion are (with percentage contributions for 2000–2004): Solid fuels (e.g., coal): 35% 2. Liquid fuels (e.g., gasoline, fuel oil): 36% 3. Gaseous fuels (e.g., natural gas): 20% 4. Flaring gas industrially and at wells: <1% 5. Cement production: 3% 6. Non-fuel hydrocarbons: < 1% 7. The "international bunkers" of shipping and air transport not included in national inventories: 4% 1.
The US Environmental Protection Agency (EPA) ranks the major greenhouse gas contributing end-user sectors in the following order: industrial, transportation, residential, commercial and agricultural. Major sources of an individual's greenhouse gas include home heating and cooling, electricity consumption, and transportation. Corresponding
conservation measures are improving home building insulation, installing geothermal heat pumps and compact fluorescent lamps, and choosing energy-efficient vehicles. Carbon dioxide, methane, nitrous oxide and three groups of fluorinated gases (sulfur hexafluoride, HFCs, and PFCs) are the major greenhouse gases and the subject of the Kyoto Protocol, which came into force in 2005. Although CFCs are greenhouse gases, they are regulated by the Montreal Protocol, which was motivated by CFCs' contribution to ozone depletion rather than by their contribution to global warming. Note that ozone depletion has only a minor role in greenhouse warming though the two processes often are confused in the media. On December 7, 2009, the US Environmental Protection Agency released its final findings on greenhouse gases, declaring that "greenhouse gases (GHGs) threaten the public health and welfare of the American people". The finding applied to the same "six key well-mixed greenhouse gases" named in the Kyoto Protocol: carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride. GREEENHOUS GAS EMISSIONS Measurements from Antarctic ice cores show that before industrial emissions started atmospheric CO2 levels were about 280 parts per million by volume (ppmv), and stayed between 260 and 280 during the preceding ten thousand years. Carbon dioxide concentrations in the atmosphere have gone up by approximately 35 percent since the 1900s, rising from 280 parts per million by volume to 387 parts per million in 2009. One study using evidence from stomata of fossilized leaves suggests greater variability, with carbon dioxide levels above 300 ppm during the period seven to ten thousand years ago though others have argued that these findings more likely reflect calibration or contamination problems rather than actual CO 2 variability. Because of the way air is trapped in ice (pores in the ice close off slowly to form bubbles deep within the firn) and the time period represented in each ice sample analyzed, these figures represent averages of atmospheric concentrations of up to a few centuries rather than annual or decadal levels.
Recent year-to-year increase of atmospheric CO2 Since the beginning of the Industrial Revolution, the concentrations of most of the greenhouse gases have increased. For example, the concentration of carbon dioxide has increased by about 36% to 380 ppmv, or 100 ppmv over modern pre-industrial levels. The first 50 ppmv increase took place in about 200 years, from the start of the Industrial Revolution to around 1973; however the next 50 ppmv increase took place in about 33 years, from 1973 to 2006. Recent data also shows the concentration is increasing at a higher rate. In the 1960s, the average annual increase was only 37% of what it was in 2000 through 2007. The other greenhouse gases produced from human activity show similar increases in both amount and rate of increase. Many observations are available online in a variety of Atmospheric Chemistry Observational Databases. Relevant to radiative forcing Increase (ppm) Increase (%) Radiative forcing over preover pre(W/m2) industrial (1750) industrial (1750)
Gas
Current (1998) Amount by volume
Carbon dioxide
365 ppm (383 ppm, 2007.01)
87 ppm (105 ppm, 2007.01)
31% (38%, 2007.01)
1.46 (~1.53, 2007.01)
Methane
1745 ppb
1045 ppb
67%
0.48
Nitrous oxide
314 ppb
44 ppb
16%
0.15
Relevant to both radiative forcing and ozone depletion; all of the following have no natural sources and hence zero amounts pre-industrial Gas
Current (1998) Amount by volume
Radiative forcing (W/m2)
CFC-11
268 ppt
0.07
CFC-12
533 ppt
0.17
CFC-113
84 ppt
0.03
Carbon tetrachloride
102 ppt
0.01
HCFC-22
69 ppt
0.03
RECENT RATES OF CHANGE IN EMISSIONS The sharp acceleration in CO2 emissions since 2000 to more than a 3% increase per year (more than 2 ppm per year) from 1.1% per year during the 1990s is attributable to the
lapse of formerly declining trends in carbon intensity of both developing and developed nations. Although over 3/4 of cumulative anthropogenic CO2 is still attributable to the developed world, China was responsible for most of global growth in emissions during this period. Localised plummeting emissions associated with the collapse of the Soviet Union have been followed by slow emissions growth in this region due to more efficient energy use, made necessary by the increasing proportion of it that is exported. In comparison, methane has not increased appreciably, and N2O by 0.25% y−1. The direct emissions from industry have declined due to a constant improvement in energy efficiency, but also to a high penetration of electricity. If one includes indirect emissions, related to the production of electricity, emissions from industry in Europe are roughly stabilized since 1994. Asia:
Atmospheric levels of CO2 continue to rise, partly a sign of the industrial rise of Asian economies led by China. Over the 2000-2010 interval China is expected to increase its carbon dioxide emissions by 600 Mt, largely because of the rapid construction of oldfashioned power plants in poorer internal provinces. United Kingdom:
The UK set itself a target of reducing carbon dioxide emissions by 20% from 1990 levels by 2010, but according to its own figures it will fall short of this target by almost 4%. United States;
The United States emitted 16.3% more greenhouse gas in 2005 than it did in 1990. According to a preliminary estimate by the Netherlands Environmental Assessment Agency, the largest national producer of CO 2 emissions since 2006 has been China with an estimated annual production of about 6200 megatonnes. China is followed by the United States with about 5,800 megatonnes. The per capita emission figures of China are about one quarter of those of the US population, but the per GDP emission figures of China are about four times those of the US due to the varying size of the nations population and GDP. Relative to 2005, China's fossil CO 2 emissions increased in 2006 by 8.7%, while in the USA, comparable CO2 emissions decreased in 2006 by 1.4%. The agency notes that its estimates do not include some CO2 sources of uncertain magnitude. These figures rely on national CO2 data that do not include aviation. Although these tonnages are small compared to the CO2 in the Earth's atmosphere, they are significantly larger than preindustrial levels.
RELATIVE CO2 EMISSION FROM VARIOUS FUELS: Pounds of carbon dioxide emitted per million British thermal units of energy for various fuels. Fuel name
CO2 emitted (lbs/106 Btu)
CO2 emitted (g/10 6 J)
Automobile gasoline
156
67.07
Aviation gasoline
153
65.78
Coal (anthracite)
227
97.59
Coal (bituminous)
205
88.13
Coal (lignite)
215
92.43
Coal (subbituminous)
213
91.57
Fuel oil
161
69.22
Kerosene
159
68.36
Liquefied petroleum gas
139
59.76
Natural gas
117
50.30
Petroleum coke
225
96.73
Propane
139
59.76
Tires/ tire derived fuel
189
81.26
Wood and wood waste
195
83.83
GLOBAL WARMING INRODUCTION Global warming is the increase in the average temperature of the planet Earth's near-surface air and oceans since the mid-20th century and its projected continuation. Global surface temperature increased 0.74 ± 0.18 ° C (1.33 ± 0.32 °F) between the start and the end of the
20th century. The Intergovernmental Panel on Climate Change (IPCC) concludes that most of the observed temperature increase since the middle of the 20th century was caused by increasing concentrations of greenhouse gases resulting from human activity such as fossil fuel burning and deforestation. The IPCC also concludes that variations in natural phenomena such as solar radiation and volcanism produced most of the warming from preindustrial times to 1950 and had a small cooling effect afterward. These basic conclusions have been endorsed by more than 40 scientific societies and academies of science, including all of the national academies of science of the major industrialized countries. Climate model projections summarized in the latest IPCC report indicate that the global surface temperature is likely to rise a further 1.1 to 6.4 °C (2.0 to 11.5 °F) during the 21st
century. The uncertainty in this estimate arises from the use of models with differing sensitivity to greenhouse gas concentrations and the use of differing estimates of future greenhouse gas emissions. Some other uncertainties include how warming and related changes will vary from region to region around the globe. Most studies focus on the period up to the year 2100. However, warming is expected to continue beyond 2100 even if emissions stop, because of the large heat capacity of the oceans and the long lifetime of carbon dioxide in the atmosphere. An increase in global temperature will cause sea levels to rise and will change the amount and pattern of precipitation, probably including expansion of subtropical deserts. Warming will be strongest in the Arctic and will be associated with continuing retreat of glaciers, permafrost and sea ice. Other likely effects include increases in the intensity of extreme weather events, species extinctions, and changes in agricultural yields. Political and public debate continues regarding global warming, and what actions (if any) to take in response. The available options are mitigation to reduce further emissions; adaptation to reduce the damage caused by warming; and, more speculatively, geoengineering to reverse global warming. Most national governments have signed and ratified the Kyoto Protocol aimed at reducing greenhouse gas emissions.
TEMPERATURE CHANGES The most commonly discussed measure of global warming is the trend in globally averaged temperature near the Earth's surface. Expressed as a linear trend, this temperature rose by 0.74 °C ± 0.18 °C over the period 1906–2005. The rate of warming over the last half of that period was almost double that for the period as a whole (0.13 °C
± 0.03 °C per decade, versus 0.07 °C ± 0.02 °C per decade). The urban heat island effect is estimated to account for about 0.002 °C of warming per decade since 1900. Temperatures in the lower troposphere have increased between 0.12 and 0.22 °C (0.22 and 0.4 °F) per decade since 1979, according to satellite temperature measurements. Temperature is believed to have been relatively stable over the one or two thousand years before 1850, with regionally-varying fluctuations such as the Medieval Warm Period or the Little Ice Age. Based on estimates by NASA's Goddard Institute for Space Studies, 2005 was the warmest year since reliable, widespread instrumental measurements became available in the late 1800s, exceeding the previous record set in 1998 by a few hundredths of a degree. Estimates prepared by the World Meteorological Organization and the Climatic Research Unit concluded that 2005 was the second warmest year, behind 1998. Temperatures in 1998 were unusually warm because the strongest El Niño in the past century occurred during that year. Global temperature is subject to short-term fluctuations that overlay long term trends and can temporarily mask them. The relative stability in temperature from 1999 to 2009 is consistent with such an episode. Temperature changes vary over the globe. Since 1979, land temperatures have increased about twice as fast as ocean temperatures (0.25 °C per decade against 0.13 °C per decade). Ocean temperatures increase more slowly than land temperatures because of the larger effective heat capacity of the oceans and because the ocean loses more heat by evaporation. The Northern Hemisphere warms faster than the Southern Hemisphere because it has more land and because it has extensive areas of seasonal snow and sea-ice cover subject to ice-albedo feedback . Although more greenhouse gases are emitted in the Northern than Southern Hemisphere this does not contribute to the difference in warming because the major greenhouse gases persist long enough to mix between hemispheres. The thermal inertia of the oceans and slow responses of other indirect effects mean that climate can take centuries or longer to adjust to changes in forcing. Climate commitment studies indicate that even if greenhouse gases were stabilized at 2000 levels, a further warming of about 0.5 °C (0.9 °F) would still occur.
EXTERNAL FORCING External forcing is a term used in climate science for processes external to the climate system (though not necessarily external to Earth) that influence climate. Climate responds to several types of external forcing, such as radiative forcing due to changes in atmospheric composition (mainly greenhouse gas concentrations), changes in solar
luminosity, volcanic eruptions, and variations in Earth's orbit around the Sun. Attribution of recent climate change focuses on the first three types of forcing. Orbital cycles vary slowly over tens of thousands of years and thus are too gradual to have caused the temperature changes observed in the past century.
