Pollutants enter the air from various sources, but burning of fossil fuels contributes the most to air pollution. * Exhaust fumes from vehicles contains soot (tiny carbon particles), lead (from cars using unleaded petrol), carbon monoxide, oxides of nitrogen and hydrocarbons due to the incomplete combustion of fossil fuels. * Burning of fossil fuels in the combustion engines of vehicles and electrical power stations also releases large amount of carbon dioxide into the atmosphere. * Human activities such as open burning cause severe smog and haze. * Industrial plants and factories also pump large amount of carbon monoxide, oxides of nitrogen and sulphur dioxide into the atmosphere. * Both oxides of nitrogen and sulphur dioxide can combine with water vapour in the atmosphere to form nitric acid and sulphuric acid respectively. * Then, they fall back to the Earth as acid rain.
* Rainwater typically has a pH value or 5.6, due to the presence of dissolved carbon dioxide, which forms carbonic acid. * The pH of acid rain is, however, less then 5.0. Major primary pollutants produced by human activity include: * Sulphur oxides (SO4) – especially sulfur dioxide, a chemical compound with the formula SO2. SO2 is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide. Further oxidation of SO2, usually in the presence of a catalyst such as NO2, forms H2SO4, and thus acid rain. This is one of the causes for concern over the environmental impact of the use of these fuels as power sources. * Nitrogen oxides (NO3) – especially nitrogen dioxide are emitted from high temperature combustion, and are also produced naturally during thunderstorms by electrical discharge. Can be seen as the brown haze dome above or plume downwind of cities. Nitrogen dioxide is the chemical compound with the formula NO2. It is one of the several nitrogen oxides.
This reddish-brown toxic gas has a characteristic sharp, biting odor. NO2 is one of the most prominent air pollutants. * Carbon monoxide (CO)- is a colourless, odourless, non-irritating but very poisonous gas. It is a product by incomplete combustion of fuel such as natural gas, coal or wood. Vehicular exhaust is amajor source of carbon monoxide. * Carbon dioxide (CO2) – a colourless, odourless, non-toxic greenhouse gas also associated with ocean acidification, emitted from sources such as combustion, cement production, and respiration. It is otherwise recycled in the atmosphere in the carbon cycle. * Volatile organic compounds – VOCs are an important outdoor air pollutant. In this field they are often divided into the separate categories of methane (CH4) and non-methane (NMVOCs). Methane is an extremely efficient greenhouse gas which contributes to enhanced global warming. Other hydrocarbon VOCs are also significant greenhouse gases via their role in creating ozone and in prolonging the life of methane in the atmosphere, although the effect varies depending on local air quality.
Within the NMVOCs, the aromatic compounds benzene, toluene and xylene are suspected carcinogens and may lead to leukemia through prolonged exposure. 1,3-butadiene is another dangerous compound which is often associated with industrial uses. * Atmospheric particulate matter – Particulates, alternatively referred to as particulate matter (PM) or fine particles, are tiny particles of solid or liquid suspended in a gas. In contrast, aerosol refers to particles and the gas together. Sources of particulate matter can be manmade or natural. Some particulates occur naturally, originating from volcanoes, dust storms, forest and grassland fires, living vegetation, and sea spray. Human activities, such as the burning of fossil fuels in vehicles, power plants and various industrial processes also generate significant amounts of aerosols. Averaged over the globe, anthropogenic aerosols—those made by human activities—currently account for about 10 percent of the total amount of aerosols in our atmosphere. Increased levels of fine particles in the air are linked to health hazards such as heart disease, altered lung function and lung cancer. * Persistent free radicals connected to airborne fine particles could cause cardiopulmonary disease. * Toxic metals, such as lead, cadmium and copper.
* Chlorofluorocarbons (CFCs) – harmful to the ozone layer emitted from products currently banned from use. * Ammonia (NH3) – emitted from agricultural processes. Ammonia is a compound with the formula NH3. It is normally encountered as a gas with a characteristic pungent odor. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to foodstuffs and fertilizers. Ammonia, either directly or indirectly, is also a building block for the synthesis of many pharmaceuticals. Although in wide use, ammonia is both caustic and hazardous. * Odors — such as from garbage, sewage, and industrial processes * Radioactive pollutants – produced by nuclear explosions, nuclear events, war explosives, and natural processes such as the radioactive decay of radon.
Secondary pollutants include:
* Particulate matter formed from gaseous primary pollutants and compounds in photochemical smog. Smog is a kind of air pollution; the word “smog” is a portmanteau of smoke and fog. Classic smog results from large amounts of coal burning in an area caused by a mixture of smoke and sulfur dioxide. Modern smog does not usually come from coal but from vehicular and industrial emissions that are acted on in the atmosphere by ultraviolet light from the sun to form secondary pollutants that also combine with the primary emissions to form photochemical smog. * Ground level ozone (O3) formed from NO3 and VOCs. Ozone (O3) is a key constituent of the troposphere. It is also an important constituent of certain regions of the stratosphere commonly known as the Ozone layer. Photochemical and chemical reactions involving it drive many of the chemical processes that occur in the atmosphere by day and by night. At abnormally high concentrations brought about by human activities (largely the combustion of fossil fuel), it is a pollutant, and a constituent of smog. * Peroxyacetyl nitrate (PAN) – similarly formed from NO3 and VOCs. Minor air pollutants include:
* A large number of minor hazardous air pollutants. Some of these are regulated in USA under the Clean Air Act and in Europe under the Air Framework Directive. * A variety of persistent organic pollutants, which can attach to particulate matter. Persistent organic pollutants (POPs) are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes. Because of this, they have been observed to persist in the environment, to be capable of long-range transport, bio accumulate in human and animal tissue, bio magnify in food chains, and to have potential significant impacts on human health and the environment.
API and Health Implications (Daily Targets)
API| Air Pollution
Level| Health Implications|
0 – 50| Excellent| No health implications|
51 -100| Good| No health implications|
101-150| Slightly Polluted| Slight irritations may occur, individuals with breathing or heart problems should reduce outdoor exercise.| 151-200| Lightly Polluted| Slight irritations may occur, individuals with breathing or heart problems should reduce outdoor exercise.| 201-250| Moderately Polluted| Healthy people will be noticeably affected. People with breathing or heart problems will experience reduced endurance in activities. These individuals and elders should remain indoors and restrict activities.| 251-300| Heavily Polluted| Healthy people will be noticeably affected. People with breathing or heart problems will experience reduced endurance in activities. These individuals and elders should remain indoors and restrict activities.| 300+| Severely Polluteded| Healthy people will experience reduced endurance in activities. There may be strong irritations and symptoms and may trigger other illnesses. Elders and the sick should remain indoors and avoid exercise. Healthy individuals should avoid outdoor activities.|
* Human activities are the main reason why water pollution in most countries has reached a critical point. * Waste matter from industrial and domestic sources that is dissolved or suspended in water contributes to the deterioration of water quality. * We have discussed how run-offs fertilizers into lakes and rivers affect the freshwater ecosystems through eutrophication. * Eutrophication occurs when inorganic nutrients and organic material enter a river or a lake. * The discharge of untreated sewage into a river also has an immediate effect on the biotic and abiotic components of the water ecosystem. * The enrichment of lakes and rivers with nutrients encourages photosynthesizing organisms in the water, particularly algae, to grow rapidly, resulting in a population explosion known as algal bloom. * The density of the algae may be so high that light intensity in the water is greatly reduced. * The death of plants and algae and the subsequent decomposition of these organisms by bacteria lead to a severe depletion of oxygen in the water, causing the death of aerobic organisms.
* The rapid growth of microorganisms in water leads to the increase in biochemical oxygen demand (BOD). * BOD refers to the amount of dissolved oxygen taken up by microorganisms that decompose organic waste matter in water. * The dissolved oxygen concentration can be used as an indicator of water pollution level. * A high BOD value indicates the presence of a large number of microorganisms and this suggests a high level of pollution. * Industrial waste can include heavy metals such as lead and mercury and radioactive waste which also find their way into rivers or lakes. * Illegal dumping of waste matter and effluent from heavy industries is the main source of heavy metal pollution. * Lead can also leak out through lead pipes which are used in plumbing. * Many of these heavy metals are highly toxic, last for a long time and can accumulate in living organisms via the food chain. * Radioactive waste can cause cancer and leukaemia.
Water Quality Index Legend
WQI| POLLUTION LEVEL| CLASS|
92.8 – 100.0| Water is very clean.| Ⅰ|
76.6 – 92.8| Water is clean with minimal pollutants.| Ⅱ|
52.5 – 96.6| Water is slightly polluted.| Ⅲ|
29.7 – 52.5| Water is polluted.| Ⅳ|
〈29.7| Water is very polluted.| Ⅴ|
* Noise from cars, motorcycles, aeroplanes, construction sites, agricultural and industrial machinery can be a form a pollution. * The noise level of residential areas should not exceed 55 decibles (dB). * According to the World Health Organisation (WHO), prolonged exposure to noise levels at or above 80 dB can cause deafness. * Exccesive exposure to noise is considered a health risk because noise can contribute to the development and aggravation of stress related problems such as high blood pressure, coronary disease, ulcers, depression and headaches.