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.
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.
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.
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.
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, 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.
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 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.
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.
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.
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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