The Sources, Health and Environmental Effects of the Common Air Pollutants
Exposure-response relationships (frequently called dose-response relationships) may be used to estimate potential impacts on people and/or the environment. The World Health Organisation (WHO) has published information on the exposure-response relationships for the most common urban air pollutants as well as Air Quality Guidelines Values.
The adverse health effects of ambient air pollution on exposed communities, demonstrated through many epidemiological studies include:
reduced lung functioning provoking asthma attacks
worsening of respiratory symptoms restricted physical activity
increased medication use
increased hospital admissions
increased emergency room visits
development of respiratory diseases premature death.
The expected health effects depend on the type of pollution, the level (pollutant concentration) and duration of exposure, and the personal susceptibility of an individual.
SO2 (Sulphur dioxide)
Sulphur dioxide is formed when fuels (mainly coal and oil products) containing sulphur is burned, and during metal smelting and other industrial processes. Vehicle fuels (petrol and diesel) contain significant levels of sulphur and hence contribute to the emission of SO2 and sulphate particulates. SO2 in the atmosphere is converted to sulphuric acid (H2SO4) and other sulphate particulates. Large scale emissions of SO2 from power stations contribute to acid rain.
Health and Environmental Effects of SO2: The major health concerns associated with exposure to high concentrations of SO2 include effects on breathing (decreased lung function), respiratory illness, alterations in pulmonary defences, and aggravation of existing cardiovascular disease. Children, the elderly, and people with asthma, cardiovascular disease or chronic lung disease (such as bronchitis or emphysema), are most susceptible to adverse health effects associated with exposure to SO2.
NOx consists of nitric oxide (NO) and nitrogen dioxide (NO2). Nitric oxide (NO) is mainly produced by combustion processes. NO is thus present in motor vehicle exhaust gases, stack emissions from stationary combustion sources such as coal, oil and diesel fired boilers, coal fired power stations and waste incinerators. The negative environmental impacts of NO are not due to direct exposure to NO but to the atmospheric transformation products of NO. About 90% of the NOx is released in the form of NO which is converted to NO2 in the atmosphere. Nitric acid plants are sources of NOx and nitrous oxide (N2O), a powerful greenhouse gas. It plays a major role in the atmospheric reactions that produce ground-level ozone (or smog) and the nitrates in fine particulate matter (PM2.5).
Health and Environmental Effects of NO2:
Nitrogen dioxide can irritate the lungs and lower resistance to respiratory infections such as influenza. The effects of short-term exposure are still unclear, but continued or frequent exposure to concentrations that are typically much higher than those normally found in the ambient air may cause increased incidence of acute respiratory illness in children. Nitrogen oxides contribute to ozone formation and can have adverse effects on both terrestrial and aquatic ecosystems. NO2 is a strong oxidizing agent that reacts in the air to form corrosive nitric acid, as well as toxic organic nitrates. Nitrogen oxides in the air contribute to acid rain and eutrophication. (Eutrophication occurs when a body of water suffers an increase in nutrients that leads to a reduction in the oxygen in the water, producing an environment that is destructive to fish and other animal life.)
Ground-level ozone (the primary constituent of smog) is the most complex, difficult to control, and pervasive of the six principal air pollutants. Unlike other pollutants, ozone is not emitted directly into the air by specific sources. Ozone is created by sunlight acting on NOx and VOC in the air. There are thousands of types of sources of these gases. Some of the common sources include petrol vapour, chemical solvents, combustion products of fuels, and consumer products. As noted earlier, emissions of NOx and VOC from motor vehicles and stationary sources can be carried hundreds of miles from their origins, and result in high ozone concentrations over very large regions.
Health and Environmental Effects of ozone: Scientific evidence indicates that ground-level ozone not only affects people with impaired respiratory systems (such as asthmatics), but healthy adults and children as well. Exposure to ozone for 6 to 7 hours, even at relatively low concentrations, significantly reduces lung function and induces respiratory inflammation in normal, healthy people during periods of moderate exercise. It can be accompanied by symptoms such as chest pain, coughing, nausea, and pulmonary congestion. Recent studies provide evidence of an association between elevated ozone levels and increases in hospital admissions for respiratory problems in several U.S. cities. Results from animal studies indicate that repeated exposure to high levels of ozone for several months or more can produce permanent structural damage in the lungs. Ozone damages crops and forest ecosystems.
CO (Carbon monoxide)
Carbon monoxide is a colourless, odourless, poisonous gas formed when carbon in fuels is not burned completely. It is a by-product of vehicle exhaust, which contributes about 60 percent of all CO emissions. In cities, vehicle exhaust can cause as much as 95 percent of all CO emissions. These emissions can result in high concentrations of CO, particularly in local areas with heavy traffic congestion. Other sources of CO emissions include industrial processes and fuel combustion in sources such as boilers and incinerators.
Health and Environmental Effects of CO: Carbon monoxide enters the bloodstream and reduces oxygen delivery to the body's organs and tissues. The health threat from exposure to CO is most serious for those who suffer from cardiovascular disease. Healthy individuals are also affected, but only at higher levels of exposure. Exposure to elevated CO levels is associated with visual impairment, reduced work capacity, reduced manual dexterity, poor learning ability, and difficulty in performing complex tasks.
The main source of environmental lead is emissions from cars using leaded petrol. Smelters and battery plants are major sources of lead in the air in their immediate vicinity. The highest concentrations of lead may be found in the vicinity of nonferrous smelters and other stationary sources of lead emissions.
Other air pollutants
Dioxins and furans (two Persistent Organic Pollutants (POPs)) are two groups of extremely harmful substances emitted from waste incinerators that are not equipped with the most sophisticated operational and emission control systems. This is one of the main reasons for communities? opposition to the use of incineration as a means of „disposal? of solid waste. (Other reasons are - incineration discourages recycling and reuse of the „waste? materials, and is wasteful of energy and other natural resources.) Particulate matter containing heavy metals (principally Pb) or persistent organic compounds (such as dioxins) contaminate soil and crops.
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