Air Pollution: Urban, Industrial, and Transborder

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Author: Susan Aldridge
Editors: Brenda Wilmoth Lerner and K. Lee Lerner
Date: 2016
Worldmark Global Health and Medicine Issues
Publisher: Gale, a Cengage Company
Document Type: Excerpt; Topic overview
Pages: 7
Content Level: (Level 5)
Lexile Measure: 1320L

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Air Pollution: Urban, Industrial, and Transborder


Air pollution is the contamination of air with substances known as pollutants that are harmful to the health of humans, animals, or plants, or which damage property. Air pollutants are either gases, liquids, or solids, and they come from a variety of sources, including industrial processes, transport, and domestic stoves.

According to the World Health Organization (WHO), air pollution was linked to around 7 million deaths around the world in 2012, mainly in low- and middle-income countries. Of these, around 4.3 million died as a result of exposure to indoor air pollution and 3.7 from outdoor air pollution. (Some deaths were linked to exposure to both indoor and outdoor pollution.) This means that air pollution is now considered to be the leading environmental health risk. In developed countries, air pollution levels have fallen in recent years because of strong environmental legislation and the adoption of cleaner energy technologies. The main problems arise in emerging economies, like China and India, where growth in industry and traffic have been allowed to emit unprecedented levels of air pollution. The other major issue is exposure to indoor air pollution from solid fuel stoves used for cooking and heating, which causes half of all deaths from pneumonia among children under the age of five.

The nature of air pollution varies with time and place, and it does not recognize national boundaries. The main gaseous pollutants are sulfur dioxide, nitrogen oxides, carbon monoxide, and hydrocarbons. Sulfur dioxide comes from burning fossil fuels, which have up to 7 percent sulfur content. Most sulfur dioxide comes from coal-fueled energy generation. If inhaled, sulfur dioxide causes, or exacerbates, respiratory disease. It also combines with moisture in the air to form sulfuric acid, or acid rain, which then deposits on surfaces. Such acid deposition damages buildings and works of art. Acid rain also affects water and soil, which damages fish and plants.

Nitrogen oxides is an umbrella term for a mixture of pollutants formed by the combustion of fossil fuels and emitted by vehicles, power stations, and industrial processes. They are formed when the combustion process oxidizes both atmospheric nitrogen and nitrogen present in the fuel itself. Initially, nitric oxide, which is harmless, is emitted, but that is soon oxidized in air to a number of secondary pollutants, including nitrogen dioxide and ground level ozone. Both have a negative impact on lung health.

Motor vehicles are also the main source of the two other major gaseous air pollutants. Carbon monoxide is a colorless, odorless gas formed through the incomplete combustion of fossil fuels. Exposure is dangerous to health because carbon monoxide binds to hemoglobin, which normally transports oxygen throughout the body. Reduced oxygenation exacerbates heart disease, and a reduced oxygen supply to the brain may be fatal. Meanwhile, hydrocarbons are also formed by incomplete fossil fuel combustion. Several hydrocarbons, such as benzene and formaldehyde, are classed as carcinogens. Hydrocarbons also contribute to the formation of ground level ozone by combining with nitrogen oxides in the presence of sunlight. Ozone is a major component of photochemical smog, a toxic combination of pollutants that contributes to poor air quality in cities like Los Angeles, California, where climatic condition and geographic location favor its formation. The smog causes coughing, chest pain, eye irritation, asthma, and bronchitis.

Particulate matter (PM) is the other significant type of air pollution and refers to a mixture of solid particles and liquid droplets present in the atmosphere. Such mixtures are known as aerosols and are composed of materials from many different sources. Major components of PM are sulfate, nitrates, ammonia, sodium chloride, black carbon, and water. Particles that come from combustion of fossil fuels are called smoke or soot and may have a particularly complex composition.

PM pollution is generally classified, and regulated, according to particle size. PM10s, also known as coarse particles, are those whose sizes range from 10 to 2.5 microns, while PM2.5s, also known as fine particles, Page 2  |  Top of Articlerange in size from 2.5 to 0.1 microns. The third category, ultrafine particles, are below 0.1 microns in size.

A doctor helps a little boy with an inhaler for his asthma. According to the U.S. Environmental Protection Agency, asthma can be caused or triggered by some types of air pollution. A doctor helps a little boy with an inhaler for his asthma. According to the U.S. Environmental Protection Agency, asthma can be caused or triggered by some types of air pollution. © Levent Konuk/ © Levent Konuk/

PM comes from industrial processes, vehicle exhausts, friction between tires and roads, and many other kinds of human activity. Particles larger than 10 microns tend to settle rapidly, but smaller ones remain airborne and may be inhaled. The distance they can penetrate into the respiratory system depends upon their size. Ultrafine particles can get into the bloodstream from the alveoli of the lungs. PM pollution has been shown to cause a number of health problems, including respiratory disease, heart disease, and lung cancer. Exposure to high levels of PM is linked to overall increases in rates of hospital admission and mortality, both daily and over time. More people are affected by PM than by any other form of pollution, according to the WHO.

Air pollution can be reduced and its impact on human health minimized by a combination of new technologies, environmental legislation and behavioral change. In the United States, the Clean Air Act was introduced in 1970 in response to concern about visible smog in many cities. It sets standards of levels of the main pollutants described above, plus lead. To achieve these standards, technologies such as catalytic converters are mandatory. Since pollution is not confined within national boundaries, legislation on a multinational and global basis is also essential. Thus the European Commission has many policies designed to combat the ill effects of air pollution. Its clean air policy package, adopted in 2013, contains measures to ensure that existing targets are met in the short term and that new air quality objectives are met by 2030. This will be done by encouraging research and innovation and promoting international cooperation on transborder air pollution.

Air quality standards vary greatly around the world. While developed countries are now seeing the fruits of environmental legislation put into place many years ago, rapid urbanization is taking its toll on developing nations, particularly India and China. In recognition of the fact that air pollution is a global health issue, the United Nations Environmental Programme and WHO have put in place many partnerships and programs aimed at improving both outdoor and indoor air quality.

Historical Background

The idea that “bad” air causes disease is an old one, found in early Indian, Chinese, and Roman writings. The miasmatic theory of disease held that cholera, the Black Page 3  |  Top of ArticleDeath, and other infectious diseases arose from breathing in noxious particles in polluted air. Indeed, the word miasma comes from the Greek word for pollution. The miasmatic theory was used to explain the spread of cholera through London and Paris in the mid-19th century, even though work on the germ theory of disease was quite advanced by this stage.

Miasma was said to be a mixture of vapor from rotting vegetation, polluted waterways, and human waste, all exacerbated by overcrowding. The diseases attributed to miasma were not the ones known today to result from air pollution. They were infectious diseases, and the miasmatic theory was eventually overtaken by the germ theory of disease. The legacy of the miasmatic theory was that it laid the basis for better sanitation from the 19th century onward, because it was recognized that there was a genuine link between foul smells and disease. However, the idea that “bad air” itself can be harmful to health, as the result of particulates from air pollution, has proven to be true.

The Industrial Revolution

With the exception of the smog that often appears over some Asian cities, most pollution today is invisible. In the past, coal smoke was the first notable form of air pollution. As early as 1273, when coal was first introduced into London, its residents were banned from burning “dirty coal.” The use of coal, both as a domestic fuel and power both factories and the railways, then rose dramatically during the Industrial Revolution.

Chimneys emitting black smoke were a common sight, and people breathing it in suffered from many health problems. Therefore, governments started to make moves to bring the emissions under control. For instance, the U.S. city governments of Chicago, Illinois, and Cincinnati, Ohio, brought in regulation to regulate emissions from factories and locomotives in the late 1800s. However, these measures could not, seemingly, keep pace with the rate of industrial development, with coal as its engine. Exposure to coal smoke continued to be a major cause of respiratory problems until the 1960s.

The Great Smog of 1952

Also known as the Big Smoke, the Great Smog descended on London on December 5, 1952, and lasted for five days, claiming the lives of about 4,000 people. There was nothing unusual about this smoke-laden fog, for similar incidents had occurred in London in 1813, 1873, 1882, 1891, 1892, and 1948. It was brought about by exceptionally cold weather, which meant that more coal was being burned than usual and also the pollution near ground level was trapped.

Analysis of the Great Smog showed that it contained tons of smoke particles, hydrochloric acid, and—probably most dangerous to health—sulfur dioxide, which was converted in the moist air into sulfuric acid. This was a toxic cocktail for all who were forced to breathe it in as they hurried home. So high was the death toll that the government took action through the Clean Air Acts of 1956 and 1968 to ban black smoke emission and require conversion to smokeless fuel. Although there was another smog in London in 1962, which killed 750 people, nothing like the Great Smog ever happened again, thanks to legislation and the spread of central heating, which has now largely replaced the coal fire in developed nations.

Impacts and Issues

In 2012, the WHO estimated that air pollution accounted for 12.5 percent (7 million) of all deaths globally, making air pollution the greatest single environmental health risk in the world. More deaths were attributed to indoor pollution (4.3 million) than outdoor (3.7 million), however there is overlap, as many people are exposed to both sources of pollution. Data collected by the WHO show a strong link between air pollution exposure and cardiovascular disease (e.g., heart disease and stroke) and cancer. It also has been linked to lung disease.

Estimates of exposure gathered by the WHO show that it is the low- and middle-income countries in the WHO regions of South-East Asia and the Western Pacific with the highest air pollution-linked mortality rates, with 3.3 million deaths linked to indoor air pollution and 2.6 million linked to outdoor air pollution, representing around 80 percent of all air pollution-related deaths.

Outdoor Air Pollution

Outdoor air pollution, also known as ambient or urban air pollution, arises from many different sources. Industrial processes may emit mixtures of toxic gases and particles whose nature depends upon the type of operation involved. Transport still largely relies upon gasoline and diesel, both of which emit polluting gases and particles when they are burned in an engine. As cities and countries develop, the volume of both industrial production and traffic tend to increase. Thus, development tends to go hand in hand with increased pollution, as has been the case in some countries in Southeast Asia and China.

Not all outdoor air pollution occurs in cities. It may be assumed that the air in the countryside must be cleaner than that in the city, but this is not always so. There have also been problems, particularly in developing countries, with burning agricultural wastes, deliberate setting of forest fires to clear land, and agro forestry activities such as charcoal production. The issue is compounded because there is less monitoring of pollution in rural areas.

An analysis of the 2012 WHO data shows that 40 percent of outdoor air pollution-related deaths arise from heart disease and 40 percent from stroke. The rest are from chronic obstructive pulmonary disease (11 percent), lung cancer (6 percent), and acute lower respiratory infection in children (3 percent). In 2013, WHO's Page 4  |  Top of ArticleInternational Agency for Research on Cancer stated that outdoor air pollution is carcinogenic to humans, with PM exposure being particularly linked to increased cancer incidence, particularly cancer of the lung.

Severe air pollution on February 25, 2014, in Beijing, China. Air quality index levels were classed as “Beyond Index” (PM2.5 of over 500 micrograms per cubic meter). Severe air pollution on February 25, 2014, in Beijing, China. Air quality index levels were classed as “Beyond Index” (PM2.5 of over 500 micrograms per cubic meter). © Hung Chung Chih/ © Hung Chung Chih/

Action on Outdoor Air Pollution

Controlling outdoor air pollution is a complex challenge requiring action on the part of governments at city, national, and international levels. Responsible management of industrial waste and the adoption of processes based upon “green” chemistry and clean/alternative energy are essential to control industrial emissions. Agricultural processes should also be regulated to minimize emissions.

Regulation of transport in order to minimize air pollution is perhaps even more difficult than the regulation of industry. In many parts of the world, gasoline is cheap, and people feel they have a right to a car as their personal means of transport. It is important to shift as soon as possible to cleaner forms of energy for transport, such as hydrogen, electricity, and biodiesel. People need to be encouraged to walk, cycle, and take public transport. To support this, investment should be made in the public transport infrastructure. Urban planning also has an important role to play, ensuring that towns and cities become more pedestrian-friendly.

Indoor Air Pollution

Indoor air pollution has received less attention than outdoor air pollution as a health issue. However, people can spend up to 90 percent of their time indoors, whether in an office or other workplace, in school, or at home. Furthermore, levels of air pollution indoors can be many times higher than they are outdoors, especially where ventilation is poor.

One particular indoor air pollution issue is exposure to fumes from solid fuel stoves. Three billion people, mostly in low- to middle-income countries, use either simple stoves or open fires that burn biomass and coal. This leads to exposures to high levels of soot particles, which can penetrate deep into the lungs. Women and young children are most at risk from these exposures, as they spend the most time around the domestic hearth.

Exposure to this so-called household air pollution leads to 4.3 million premature deaths a year, according to 2012 WHO data. These deaths come from stroke, heart disease, chronic obstructive pulmonary disease, and lung cancer. Exposure also doubles the risk for childhood pneumonia.

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At present, and for the foreseeable future, the population of China is set to pay a heavy price for its rapid economic development. The WHO Global Burden of Disease report states that 1.2 million people died in China and North Korea in 2010 as a result of air pollution. Research published in the Proceedings of the National Academy of Sciences in 2013 sounded a further alarm by noting that air pollution in recent years has led to the loss of more than 2.5 billion years of life expectancy in China. In other words, prosperity is being accompanied by a reduction of 5.5 years in life expectancy for the average Chinese citizen.

China's air pollution problems are well known. First of all, the smog that often envelops Beijing and other Chinese cities is highly visible, even from space. Late in 2013, the moderate resolution imaging spectroradiometer aboard the National Aeronautics and Space Administration satellite Terra captured a 750 mile swath of smog stretching between Beijing and Shanghai. Second, the U.S. embassy in Beijing monitors PM2.5 levels every hour and posts these online and on Twitter, so anyone in the world can become aware of air quality in the city in real time. From this information, it is evident that PM2.5 levels in the city are often far beyond the 25 micrograms per cubic meter (µg/m3) 24-hour mean set by the WHO. On occasion, they have reached 500 µg/m3 or even as high as 1,000 µg/m3.

China's growing economy relies very heavily on coal. Beginning early in the first decade of the 21st century, the country has undergone mass industrialization, with an accompanying dramatic growth in road transport, serving to compound the air pollution problem. The smog that often hangs over Chinese cities and towns resembles that which plagued London in earlier years. However, the Chinese smog likely also contains sulfur dioxide, nitrogen oxides, carbon monoxide, ground level ozone, and PM2.5s (the exact composition is not known because sources are said to be various and complicated).

The problems caused by China's smog are both immediate and long term. On several occasions, reduced visibility has caused the closure of airports in several cities. Children have also been kept away from school when PM2.5 levels have soared, out of concern for the health of those with asthma. These air pollution emergencies hit both tourism and business, with people fearing they will become ill if they visit China during an air pollution episode.

Air pollution is also exacting a severe toll on the health of the Chinese population. According to Greenpeace China, PM2.5 exposure caused nearly 10,000 premature deaths and 70,000 hospital visits or admissions in the Beijing-Tianjin-Hebei region in 2011. Meanwhile, Chinese scientists are noting a change in the pattern of lung cancer seen in Beijing in recent years. There are more cases of adenocarcinoma, which is linked to air pollution, and fewer cases of squamous cell lung cancer, which is more likely to be caused by smoking. They expect to see many more cases of adenocarcinoma in the next few years because even if there is a dramatic improvement in air quality in Beijing, lung cancer takes many years to develop; in most cases, damage to cells that will develop into a tumor has already been done. The researchers are also linking exposure to PM2.5 pollution to reduced birth weight and premature birth.

To improve the quality of air in its towns and cities, China needs to reduce its dependence on coal. If possible, the government needs to find ways of doing this without compromising the continued economic growth that its population expects. In 2013, the government released its national Airborne Pollution Action Plan. This calls for a 10 percent reduction of PM10 levels by 2017 in 338 of China's cities. In Beijing, Tianjin, and Hebei, where pollution problems are generally worse than elsewhere, PM2.5 levels must be reduced by 25 percent by 2017.

Other measures include banning heavily polluting vehicles from city streets by 2017 and extending air monitoring to all Chinese cities. Natural gas and nuclear power capacity will be increased in order to decrease dependence on coal. The proportion of coal in China's energy mix should therefore fall 3 percent by 2017. There are also local plans to improve air quality. For instance, Beijing aims to reduce it PM2.5 levels to 60 µg/m3, which may be a realistic target, but that is still higher than the WHO 24-hour mean level of 25 µg/m3.

Action on Household Air Pollution

The WHO has issued new air quality guidelines that contain recommendations on performance of solid fuel heaters and stoves. It is also working to integrate guidance and resources for clean household energy into global child health initiatives. There are a number of specific measures that could reduce household pollution. The most important is a switch from solid fuels to cleaner and more efficient fuels and technologies, including liquefied petroleum gas, biogas, producer gas, electricity, and solar power.

Where access to these clean fuels is still limited, the focus should be upon using improved stoves, which emit less smoke if they are properly designed, installed, and maintained. Improved ventilation of the cooking and living area should also be encouraged to reduce exposures to smoke. Installation of chimneys, smoke hoods, enlarged windows, and eave spaces can help get away from the dangerously confined cooking or heating space. Finally, advising users to dry their fuel before burning it and keeping young children away from smoke supports the other smoke reduction measures.

Air Quality Guidelines

The WHO first issued guidelines on selected air pollutants in 1987, updated these in 1997, and again in 2005. In the guidelines, upper limits are set for PM, ozone, nitrogen oxides, and sulfur dioxide, according to the latest scientific evidence on the effects of air pollution on health. The guidelines provide targets for various policy options aimed at improving air quality around the world. There are also, in many countries, national air Page 6  |  Top of Articlequality standards that may vary according to local conditions and capacity to make improvements.

Particulate matter pollution is measured as µg/m3 and levels for PM10 are 20 (annual mean) and 50 (24-hour mean) and for PM2.5 10 (annual mean) and 25 (24-hour mean). The upper limit for PM2.5 reflects the greater health hazard associated with the smaller particles. For ground level ozone, the upper limit is 100 µg/m3 (8-hour mean), for nitrogen oxides 40 µg/m3 (annual mean) and 700 µg/m3 (1-hour mean), and for sulfur dioxide 20 µg/m3 (24-hour mean) and 500 µg/m3 (10-minute mean). Air quality monitoring stations can be found at many locations in cities around the world, and they regularly post data on the Internet, so it is clear how well the location is performing with respect to WHO guidelines.

Future Implications

Air pollution is an inevitable consequence of human activity. It cannot be eliminated and will only grow as countries continue to develop. To mitigate the effect of both indoor and outdoor pollution on human health, it will be necessary to apply new and cleaner technologies for industry, transport, and household activities, within a strong framework on environmental legislation.

Reports in 2014 that the European Commission (EC) would consider relaxing air pollution legislation in the interest of reducing debt and creating jobs highlighted that bringing air pollution to the top of the political agenda will continue to be a challenge. The EC has proposed delegating air pollution legislation to national level, which would make it harder to deal with transborder pollution. Opponents of tough legislation argue that businesses will locate to countries where environmental law is weak or nonexistent. There is clearly still some way to go in convincing both the public and industry of the short- and long-term benefits of cleaner air.

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Ambient (Outdoor) Air Quality and Health

SOURCE “Ambient (Outdoor) Air Quality and Health,” Fact Sheet No. 313, Updated March 2014, World Health Organization (WHO). (accessed January 25, 2015).

INTRODUCTION The primary source that follows is taken from a fact sheet compiled by the World Health Organization. It presents the background and key points of the air pollution issue from a global perspective.

Key facts
  • Air pollution is a major environmental risk to health. By reducing air pollution levels, countries can reduce the burden of disease from stroke, heart disease, lung cancer, and both chronic and acute respiratory diseases, including asthma.
  • The lower the levels of air pollution, the better the cardiovascular and respiratory health of the population will be, both long- and short-term.
  • The “WHO Air quality guidelines” provide an assessment of health effects of air pollution and thresholds for health-harmful pollution levels.
  • Ambient (outdoor air pollution) in both cities and rural areas was estimated to cause 3.7 million premature deaths worldwide in 2012.
  • Some 88% of those premature deaths occurred in low-and middle-income countries, and the greatest number in the WHO Western Pacific and South-East Asia regions.
  • Policies and investments supporting cleaner transport, energy-efficient housing, power generation, industry and better municipal waste management would reduce key sources of urban outdoor air pollution.
  • Reducing outdoor emissions from household coal and biomass energy systems, agricultural waste incineration, forest fires and certain agro-forestry activities (e.g. charcoal production) would reduce key rural and peri-urban air pollution sources in developing regions.
  • Reducing outdoor air pollution also reduces emissions of CO and short-lived climate pollutants such as black carbon particles and methane, thus contributing to the near- and long-term mitigation of climate change.
  • In addition to outdoor air pollution, indoor smoke is a serious health risk for some 3 billion people who cook and heat their homes with biomass fuels and coal.

Outdoor air pollution is a major environmental health problem affecting everyone in developed and developing countries alike.

WHO estimates that some 80% of outdoor air pollution-related premature deaths were due to ischaemic heart disease and strokes, while 14% of deaths were due to chronic obstructive pulmonary disease or acute lower respiratory infections; and 6% of deaths were due to lung cancer.

Some deaths may be attributed to more than one risk factor at the same time. For example, both smoking and ambient air pollution affect lung cancer. Some lung cancer deaths could have been averted by improving ambient air quality, or by reducing tobacco smoking.

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A 2013 assessment by WHO's International Agency for Research on Cancer (IARC) concluded that outdoor air pollution is carcinogenic to humans, with the particulate matter component of air pollution most closely associated with increased cancer incidence, especially cancer of the lung. An association also has been observed between outdoor air pollution and increase in cancer of the urinary tract/bladder.

Ambient (outdoor air pollution) in both cities and rural areas was estimated to cause 3.7 million premature deaths worldwide per year in 2012; this mortality is due to exposure to small particulate matter of 10 microns or less in diameter (PM10), which cause cardiovascular and respiratory disease, and cancers.…

The latest burden estimates reflect the very significant role air pollution plays in cardiovascular illness and premature deaths—much more so than was previously understood by scientists.



Godish, Thad, Wayne Davis, and Joshua Fu. Air Quality, 5th ed. Boca Raton, FL: CRC Press, 2014.

Gurjar, Bhola, and Luisa Molina. Air Pollution: Health and Environmental Impact. Boca Raton, FL: CRC Press, 2010.

Jackson, Lee. Dirty Old London: The Victorian Fight against Filth. New York: yale University Press, 2014.

Khare, Mukesh. Air Pollution—Monitoring, Modelling and Health. Rijeka, Croatia: InTech, 2012.


“Ambient (Outdoor) Air Quality and Health,” Fact Sheet No. 313. World Health Organization (WHO), March 2014. (accessed February 10, 2015).

“Burden of Disease from Air Pollution for 2012.” World Health Organization (WHO). (accessed February 10, 2015).

“The Great London Smog of 1952.” Met Office Education. (accessed February 10, 2015).

Kaiman, Jonathan. “China's Toxic Air Pollution Resembles Nuclear Winter, Say Scientists.” Guardian, February 25, 2014. (accessed February 10, 2015).

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Susan Aldridge

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Gale Document Number: GALE|CX3628100010

Disclaimer:   This information is not a tool for self-diagnosis or a substitute for professional care.