Pollution I
Project
INTRODUCTION
Pollution, contamination of the environment by man-made substances or energy that have adverse effects on living or non-living matter. This contamination of air, water, or soil materials interferes with human health, health, the quality of life, or the natural functioning of ecosystems. In simple terms, pollution can be seen as the wrong substance in the wrong place in the wrong quantities at the wrong time. This implies that harm is caused to the environment, and if the same substance is present at levels too low to cause harm, then it can be considered as contamination. contamination. Many substances that can be pollutants also occur naturally, in which case they are not classified as pollution. However, other pollutants result entirely from human activity, such as most toxic organic compounds and artificial forms of radioactivity, particularly from nuclear waste.
II
TYPES OF POLLUTION
Pollution can be categorized according to the medium in which it occurs: atmospheric pollution (see Air Pollution), freshwater and sea pollution (see Water Pollution), or land pollution ( see Solid Waste Disposal). However, transfers can occur in both directions between the atmosphere, water, and the land, with consequences for both the spread of pollution and its effects. For example, the emission of sulphur dioxide—caused by the combustion of fossil fuels such as gas, petroleum, and coal—into the air can result in the acidification of soils and lakes when it reaches the Earth’s surface (see Acid Rain). Pollution can also be classified on the basis of the type of pollutant, such as pesticides (see (see Pest Control) and other persistent toxic organic compounds, heavy metals, radioactivity, human and animal effluent, and toxic gases. The most familiar forms of pollution result from the chemical properties of the substances concerned, but the physical properties may also be important, for example ionizing radiation, noise pollution, and excessive heat. Water pollution arises from the discharge of industrial, agricultural, and human wastes into freshwaters, estuaries, and seas. This may result in the poisoning of aquatic organisms or the depletion of oxygen owing to excessive growth of micro-organisms (anthropogenic eutrophication), which makes less of the water habitable for fish. Metal pollution and toxic organic compounds are of concern for human and environmental health as a result of discharges to water, air, and the terrestrial environment. Air pollution can result in adverse effects on health, crops, natural ecosystems, materials, and visibility. The major concerns over
air pollution are acidification acidification of soils and waters with its detrimental affects on animal and plant life, and the impact of traffic-derived pollutants on health in cities (see Traffic Pollution). On a global scale air pollution probably represents the greatest problem of all, with greenhouse gases (such as carbon dioxide) resulting in global warming and synthetic chlorine compounds (chlorofluorocarbons) depleting the stratospheric ozone layer. Nuclear waste is a further modern environmental concern, which poses a problem not just for the present generation, but for future generations as the waste remains radioactive for thousands of years.
III
TRENDS IN POLLUTION POLLUTION
Trends in pollution are difficult to determine accurately, particularly on a world scale. The bestdocumented trend is the global increase in carbon dioxide at a rate of about 0.5 per cent per year. Overall, there is a trend for decreasing levels of pollutants in the developed world, but the opposite in many developing countries as they rapidly industrialize. For example, it has been predicted that sulphur dioxide emissions will fall by 63 per cent in Europe from 1990 to 2010, while they will rise in China by 118 per cent. The reductions in the developed world result largely from environmental legislation, which has led to the introduction of control measures and cleaner technology. Examples are the introduction of more advanced wastewater treatment processes, shifts to cleaner fuels, and the recycling of potential contaminants.
Air Pollution I
INTRODUCTION
Air Pollution, contamination of the atmosphere by gaseous, liquid, or solid wastes or byproducts that can endanger human health and the health and welfare of plants and animals, or can attack materials, reduce visibility, or produce undesirable odours. Among air pollutants emitted by natural sources, only the radioactive gas radon is recognized as a widespread major health threat, although gases and particles from volcanic eruptions can cause serious more localized problems. A by-product of the radioactive decay of uranium minerals in certain kinds of rock, radon seeps into the basements of homes built on these rocks, posing a risk of lung cancer to residents. Each year industrially developed countries generate billions of tons of pollutants. The most prevalent and widely dispersed air pollutants are described in the accompanying table. The level is usually given in terms of atmospheric concentrations (micrograms of pollutants per cubic metre of air) or, for gases, in terms of parts per million, that is, millilitres of gas per thousand litres of air. Many come from directly identifiable sources; sulphur dioxide, for example, comes from electric power plants burning coal or oil. Others are formed through the action of sunlight on previously emitted reactive materials (called precursors). For example,
ozone, a dangerous pollutant in smog, is produced by the interaction of hydrocarbons and nitrogen oxides under the influence of sunlight. Ozone also causes serious crop damage. On the other hand, the discovery in the 1980s that air pollutants such as fluorocarbons are causing a loss of ozone from the Earth's protective ozone layer has caused the phasing out of these materials. A further category of air pollution is heavy metals, present as particulates and arising from many industrial processes.
II
METEOROLOGY AND HEALTH EFFECTS
Pollutant concentration is reduced by atmospheric mixing, which depends on such weather conditions as temperature, wind speed, and the movement of high and low pressure systems and their interaction with the local topography, for example, mountains and valleys. Normally, temperature temperature decreases with altitude. But when a colder layer of air settles under a warm layer, producing a temperature or thermal inversion, atmospheric mixing is retarded and pollutants may accumulate near the ground. Inversions can become sustained under a stationary highpressure system coupled with low wind speeds. Periods of only three days of poor atmospheric mixing can lead to high concentrations of hazardous materials in high-pollution areas and, under severe conditions, can result in injury and even death. An inversion over Donora, Pennsylvania, in 1948 caused respiratory illness in over 6,000 people and led to the deaths of 20. Severe pollution in London took 3,500 to 4,000 lives in 1952 and another 700 in 1962. Release of methyl isocyanate into the air during a temperature temperature inversion caused the disaster at Bhopal, India, in December 1984, with at least 3,300 deaths and more than 20,000 illnesses. The effects of long-term exposure to low concentrations are not well defined; however, those most at risk are the very young, the elderly, smokers, workers whose jobs expose them to toxic materials, and people with heart or lung disease. Other adverse effects of air pollution are injury to livestock and crops. Often, the first noticeable effects of pollution are aesthetic and may not necessarily be dangerous. These include visibility reduction due to tiny particles suspended in air, or bad odours, such as the rotten egg smell produced by hydrogen sulphide emanating from pulp and paper mills.
III
SOURCES SOURCES AND CONTROL
The combustion of coal, oil, and petrol accounts for much of the airborne pollutants. About 60 per cent of the sulphur dioxide and 20 per cent of the nitrogen oxides emitted into the atmosphere in the United Kingdom are produced by fossil-fuel-fired electric power plants. About 70 per cent of the carbon monoxide and 50 per cent of the nitrogen oxides come from burning petrol and diesel in cars and lorries. Other major pollution sources include iron and steel mills; smelters; municipal incinerators; oil refineries; cement plants; and nitric and sulphuric acid plants.
Potential pollutants may exist in the materials entering a chemical or combustion process process (such as sulphur in coal), or they may be produced as a result of the process itself. Carbon monoxide, for example, is a typical product of internal-combustion engines. Methods for controlling air pollution include removing the hazardous material before it is used, removing the pollutant after it is formed, or altering the process so that the pollutant is not formed or occurs only at very low levels. Car exhaust pollutants can be controlled by burning the fuel as completely as possible, by recirculating fumes from fuel tank, carburettor, and crankcase, and by changing the engine exhaust to harmless substances in catalytic converters. Industrially emitted particulates may be trapped in cyclones, electrostatic precipitators, and filters. Pollutant gases can be collected in liquids or on solids, or incinerated into harmless substances.
IV
LARGE-SCALE EFFECTS
The tall smokestacks used by industries and utilities do not remove pollutants but simply boost them higher into the atmosphere, thereby reducing their concentration at the site. These pollutants may then be transported over large distances and produce adverse effects in areas far from the site of the original emission. Sulphur dioxide and nitrogen oxide emissions from Britain and other industrialized countries of Western and Central Europe have caused acid rain in Norway and Sweden. The pH level, or relative acidity, of many freshwater lakes has been altered so dramatically by acid rain that entire fish populations have been destroyed. Sulphur dioxide emissions and the subsequent formation of sulphuric acid can also be responsible for the attack on limestone and marble at large distances from from the source. There are also claims
that acid rain has caused widespread damage to forests in Europe, but the precise role is unclear and earlier predictions of large-scale forest death are unfounded.
The worldwide increase in the burning of coal and oil since the late 1940s has led to everincreasing concentrations of carbon dioxide. The resulting “greenhouse effect”, which allows solar energy to enter the atmosphere but reduces the reemission of infrared radiation from the Earth, may well lead to a warming trend that might affect the global climate and lead to a partial melting of the polar ice-caps. Possibly an increase in cloud cover or absorption of excess carbon dioxide by the oceans (in the so-called carbon cycle) would check the greenhouse effect before it reached the stage of polar melting. Nevertheless, many research reports released during the 1990s have indicated that the greenhouse effect is definitely under way and that the nations of the world should be taking immediate steps to deal with it. In June 1999 a massive cloud of air pollution, roughly the size of the United States, was discovered 1 km to 3 km ( mi to 2 mi) above above the Indian Ocean. Ocean. The thick brown haze haze included soot, sulphates, sulphates, nitrates, mineral dust, and significant amounts of gases such as carbon monoxide and sulphur dioxide. Scientists believe it was created by human activities, especially the burning of fossil fuels, and could have a significant impact on the regional and global climate, as well as plant and animal life.
V
ACTION BY GOVERNMENTS
Various countries have set standards in legislation in the form of concentration levels that are believed to be low enough to protect public health. Source emission standards are also specified to limit the discharge of pollutants into the air so that air-quality standards will be achieved. However, the nature of the problem requires the implementation of international
environmental treaties, and to this end 49 countries agreed in March 1985 on a United Nations convention to protect the ozone layer. This “Montreal Protocol”, which was renegotiated in 1990 and 1992, called for the phaseout of certain chlorocarbons and fluorocarbons by the end of the century and provides aid to developing countries in making this transition. In addition, several international protocols have been aimed specifically at reducing the incidence of acid rain. In December 1999 the Montreal Protocol announced that almost all production and consumption of virgin ozone depleting substances had been phased out in the developed world. Similar control measures were introduced for developing countries in July 1999, and it was anticipated that all developing countries would be able to meet their freeze targets and subsequent obligations under the protocol. Concern over trans-boundary air pollution, including acid rain, in Europe has led to the United Nations Economic Commission for Europe (UNECE) developing air quality guidelines, called Critical Loads and Levels, which represent thresholds below which it is believed that damage will not occur to different ecological systems. Critical Loads are based on the amount of acidity that an ecosystem can tolerate being deposited indefinitely. Critical Levels are concentrations of ozone, sulphur dioxide, and nitrogen oxides over different averaging times and applicable to different categories of vegetation. Massive cuts are being made in emissions in Europe in order to move towards these thresholds. thresholds. In contrast, in many developing countries, pollutant concentrations are rising very rapidly due to increased industrialization and motor traffic; concern in such places is primarily with impacts on human health in cities. The World Health Organization has published air quality guidelines designed to protect health. Air Pollutants Sources of major air pollutants include individual actions, such as driving a car, and industrial activities, such as manufacturing products or generating electricity. The World Health Organization (WHO) is one of a number of bodies which publish recommended limits for human exposure to pollutants. Note: 1 cubic metre (1m3) is equal to 35.3 cu ft; 1 milligram (1 mg) is equal to 0.00004 oz; 1 microgram (1µg) is equal to 0.00000004 oz.
POLLUTA POLLUTANT NT MAJOR SOURCES SOURCES COMMENTS/WHO COMMENTS/WHO GUIDELINES GUIDELINES
Carbo Ca rbon n mon monox oxide ide (CO (CO))
Motorr-v Moto -vehi ehicle cle ex exha haust ust;; some some industrial processes
Health guidelines: 10 mg/m3 (10 ppm) over 8 hr; 30 mg/m3 over 1 hr (30 ppm)
Sulphur dioxide (SO2)
Heat and power generation facilities that use oil or coal containing sulphur; sulphuric acid plants; smelters
Health guidelines: 125 µg/m -3 (0.044 ppm) over 24 hr; 500 µg/m3 over 10 min (0.175 ppm)
PM10 parti particula culate te matter matter
Motor-ve Motor -vehicl hicle e exhaust; exhaust; indust industrial rial processes; refuse incineration; heat and power generation; reaction of pollution gases in the atmosphere
Health guideline: 70 µg/m3 over 24 hr; composed of carbon, nitrates, sulphates, and many metals including lead, copper, iron, and zinc
Lead (Pb)
Motor-vehicle exhaust; lead smelters; battery plants
Health guideline: 0.5 µg/m-3 over a year
Nitrogen oxides (NO, NO2) Motor-vehicle Motor-vehicle exhaust exhaust;; heat and Health guideline: 40-50 µg -3 (0.02-0.08 ppm) power generation; nitric acid; over 1 year; 200 µg/m3 over 1 hr (0.11 ppm) explosives; fertilizer plants for NO2; react with hydrocarbons and sunlight to form photochemical oxidants
Photochemical oxidants Formed in the atmosphere by (primarily ozone [O3]; also reaction of nitrogen oxides, peroxyacetyl nitrate [PAN] hydrocarbons, and sunlight and aldehydes)
Health guideline: 120 µg/m -3 (0.006 ppm) over 8 hr; 100-120 µg/m3 over 3 hr (0.05-0.06 ppm)
Non-methane hydrocarbons (includes ethane, ethylene, propane, butanes, pentanes, acetylene)
Motor-vehicle emissions; solvent React with nitrogen oxides and sunlight to form evaporation; industrial photochemical oxidants processes; solid waste disposal; fuel combustion
Carbon dioxide (CO 2)
All combustion sources
Possibly injurious to health at concentrations greater than 5,000 ppm over 2-8 hr; atmospheric levels have increased from about 280 ppm a century ago to over 350 ppm at present; this trend is contributing to the greenhouse effect
Note: 1 cubic metre (1 m3) is equal to 35.3 cu ft; 1 milligram (1 mg) is equal to 0.00004 oz; 1 microgram (1 µg) is equal to 0.00000004 oz; while ppm is parts per million.
Noise Pollution I
INTRODUCTION
Noise Pollution, adverse effects of noise in our living and working environment. Noise is, by definition, unwanted sound. It may be annoying, it may interfere with speech communication, leisure, or relaxation, and, at very high levels which may occur at work or during certain noisy leisure activities, it may result in hearing loss by causing damage to the hair-cells in the cochlea in the inner ear. Rather than leading to significant adverse physiological responses, however, noise is more often a major problem in terms of quality of human life in specific localities.
II
REACTIONS TO NOISE
“Annoyance” tends to be used to describe the general feeling of aggravation or vexation caused by noise nuisance. nuisance. It is the end of the noise/disturbance/annoyance chain. General long-term annoyance is the most convenient and relevant measure of the impact of noise on the community. It takes account of all the adverse effects of noise such as disturbance. Studies have been carried out to examine the relationship between exposure to noise from specific sources (the noise dose) and the annoyance caused (the response). Even though there is a wide variation in the annoyance reactions of individuals, the information can be used to define the “average” dose-response relationship, or the percentage of the population likely to display a specific degree of annoyance to a defined level of noise. When the noise is at a sufficiently high level the opinions may be clear-cut; the noise is the main factor in determining annoyance. At lower levels of noise, the general attitudes of the community as a whole, or of individual members of the community, towards the noise source, may assume greater importance. The degree of annoyance may be influenced by the length of time to which a community or an individual has been exposed to noise, and by the time of occurrence.
A
Sleep Disturbance
Research has shown that many factors affect sleep quality. About 20 per cent of the population have sleeping difficulties which are totally unrelated to noise. Age, sex, attitudes, and health factors override the impact of noise-induced sleep disturbance. Background noise levels, habituation, bedroom location, time of night, and the character of any intruding noise also influence sleep quality. Bearing this in mind, it is unrealistic and often impractical to set noise limits to ensure that sleep will not be affected in any way.
III
DESCRIBING NOISE
The level of environmental noise is normally measured with a Sound Level Meter using the Aweighted decibel scale (dB(A)). The decibel (dB) is the scale which is used to describe the sound-pressure level of the sound. It is the logarithm of the ratio of the measured sound pressure (which is what the eardrum detects) relative to a reference value, which is a very small sound pressure which automatically acquires the value 0dB. For every ten-fold increase in sound pressure, the sound-pressure level increases by 20dB. The term “A-weighting” means that the signal is filtered in a way that approximates to the frequency sensitivity of the human ear. However, the level of noise originating from a source is not the only consideration affecting its impact; duration is also important. Sometimes the noise is intermittent intermittent (for example, aircraft aircraft or train noise), while sometimes it is more or less continuous (such as motorway or factory noise). So, where separate noise events are clearly distinguishable, the important factors are the maximum level and duration of each event and the number of events in a given period, while continuous noise is averaged in some way over the exposure duration. Different methods have been devised to describe the varying temporal characteristics of different sources, but the most widely used descriptive standard for environmental noise is the Equivalent Continuous Noise Level (LAeq). LAeq describes the noise (in dB(A)) in terms of the A-weighted acoustical energy of the noise averaged over a specific time period, and is defined as the level of continuous noise that would have the same acoustical energy as the actual noise over the same time period. However, equal values of L Aeq for different sources do not necessarily elicit the same community reaction. The different characteristics of the noise, both temporal and spectral, are factors which play an important role in determining response, which cannot be adequately described by a measure of the noise alone. These differences are normally taken into account when defining standards and in noise guidelines such as the UK Planning Policy Guidance PPG 24.
IV
NOISE STANDARDS
It is possible to estimate the proportion of the population exposed to specific environmental noise levels. Taken together with information from studies of dose-response relationships, it is then possible to identify the impact of noise on the community as a whole, in terms of the proportion of the population likely to be adversely affected by noise. This information is essential when planners, lawyers, technical experts, and economists have to define noise targets and goals. The targets, taking costs and benefits into account, may range from “ideal long-term” to “practicably achievable in the shorter term”. These targets, in turn, influence noise emission (source noise level) and immission (environmental noise exposure) standards and legislation, such as the United Kingdom Environmental Protection Act 1990.
For example, a report published by Stockholm University for the World Health Organization in 1995 has concluded that noise levels outside dwellings should not exceed 55dB(A) to protect the majority of people from being seriously annoyed, and that 50dB(A) should be considered the maximum desirable. These levels can be considered as ideal targets, but because of technical, financial, and practical considerations, exposure levels higher than these will remain commonplace in the developed world for some time to come, and noise-exposure standards will be set at higher levels, although efforts will continue to be made to reduce them. International noise-emission standards are designed to control the noise emitted by specific machines, such as aircraft, cars, or industrial equipment. Environmental noise exposure standards and legislation are, on the other hand, normally devised by national or local authorities to provide an acceptable noise environment for their specific conditions. Noise immission levels depend not only on the noise emitted by particular sources, but also the distance from the source, and the use of noise attenuation measures such as noise barriers or double glazing which may be required to meet national or local noise immission standards. In order to ensure that noise levels can be predicted to an acceptable degree of accuracy and in a consistent manner, most countries have published official methods for calculating noise exposure for road traffic, aircraft, railways, and other types of noise source.
V
NOISE IN THE COMMUNITY
The main sources of noise pollution in the community are transport sources such as aircraft taking off and landing, road traffic, and railways; fixed industrial and commercial installations; construction activities; and (increasingly) leisure activities. Noise from neighbours (stereo systems, late-night comings and goings, children, barking dogs) now causes more reported complaints than any other source, but quantifying the offending noise level is often a part of this type of problem, which is more a question of considerate behaviour than noise limits. The noise level is also dependent on the building’s construction and the attenuation it provides between dwellings.
A
Road Traffic
Road traffic noise is the most widespread noise source in developed countries. A study carried out for the European Commission by the French institution INRETS in 1994 estimated that some 200 million people in the European Union (60 per cent of the population) were exposed to levels of road traffic noise exceeding 55dB(A), and some 132 million (39 per cent) to 60dB(A). In order to reduce exposure, noise emission limits have been defined for all new vehicle types. The limits have been progressively lowered lowered over the years, so that the noise emitted by new vehicles at the beginning beginning of the 21st century was some 8 to 10 dB lower than 25 years before. Most of this effort has reduced the noise from car engines and ancillary equipment so much that tyre noise, even on urban roads, is becoming the dominant source, and “quiet” road surfaces are now being used for some new roads, and quieter tyre designs
being considered. However, despite these efforts, the report predicted that traffic-noise exposure levels would increase, particularly in the quieter areas, for the subsequent 10 to 20 years because of the growth in the number of vehicles.
B
Railways
Although railways railways are generally seen as the safest, most economical, and most environmentally friendly of all conventional transport systems, many countries are now reappraising the cost of new railways in terms of environmental impact. This has been particularly true with high-speed railways. The latest high-speed trains have been designed to be no noisier than the older and slower conventional trains, but careful planning of new routes and provision of noise abatement procedures are still needed to meet environmental standards. However, trains create a less extensive noise burden than road traffic, so that, overall, the noise environment may improve.
C
Aircraft
Concern about aircraft noise grew rapidly after World War II and, by the mid-1960s, it had reached such a level that aviation authorities and manufacturers realized that noise from the early jet engines needed to be controlled and reduced in order to create a more acceptable environment. The predominant source of noise from both jet and propeller-driven aircraft is the power plant itself. The pressures from environmental lobbies have driven authorities to establish legislation to control aircraft noise by certification and the manufacturers have made great strides to reduce noise from the engines themselves. Noise levels have fallen by about 20dB since the days of the early jet aircraft, which, even though they are now larger and carry more passengers, have become far more fuel-efficient and less noisy. Whereas the early jet engine was dominated by the jet noise and compressor whine, whine, the latest high-bypass high-bypass ratio engine is characterized by fan noise both to the front and rear of the engine and the relatively low level of jet noise. While much of the work which has resulted in lower noise emission levels from jet aircraft was driven by the need to comply with noise certification requirements, public concern about the noise around airports led to the introduction of noise exposure standards or limits which are generally based on LAeq. Noise exposure contours, normally computer generated, are used to give an indication of the likely noise impact at any particular location in the vicinity of an airport. Computer modelling can also be used to evaluate the impact of any changes, such as modifications to arrival or departure routes, or the replacement of older, noisier aircraft with newer, quieter ones.
However, it must always be borne in mind that noise exposure contours will never give a precise prediction of community response.
D
Industry
Most manufacturing and industrial operations create noise. In many cases this may be limited to the plant’s interior, while in others it will affect the communities in the neighbourhood. neighbourhood. Although the community noise problem was formerly restricted mainly to heavy manufacturing industry, this is not necessarily the case today, and small manufacturing or service businesses which create noise may be located close to residential properties. The introduction of improved ventilation and heating systems has resulted in the installation of powerful fans located in the walls and roofs of buildings which can, if badly positioned, lead to significant noise levels in the neighbourhood, especially at night.
E
Construction
Construction activities activities are noisy and have the potential to cause disturbance in the surrounding communities. Some sources will generate continuous steady levels (such as fans, extractors, or compressors), some will be intermittent (such as sawing or drilling), while others will be impulsive (such as piling). Environmental noise assessments take the short-term nature of most construction activities into account by allowing higher levels than would normally be considered appropriate for long-term noise exposure.
F
Social Noise
Neighbours make noise; in fact, noise from the living and social habits of our neighbours is generating more complaints than any other single source of noise. Sources include domestic equipment, stereo and TV, animals and children, do-it-yourself activities, and lawn mowers. Many of these complaints may be a consequence of poor insulation insulation between multi-occupier dwellings—which could be improved at the design stage, but not after construction. Unreasonable and antisocial behaviour causes a great deal of noise nuisance, but it is essentially a social rather than an engineering issue. The UK Noise and Statutory Nuisance Act 1993 now provides powers to authorities to seize noisy equipment such as stereo systems if the owner does not comply with an order to reduce the noise level. The growing sophistication of leisure activities over the past few years has led to an increase in noise levels in recreational areas, with an associated increased potential for nuisance to nearby residents and other visitors. Sources include power boats, microlight aircraft, motor cycles, motor racing, clay pigeon shooting, pop concerts, and model aircraft flying. Codes of practice and planning regulations are used by the activity organizers and local authorities in
order to minimize the disturbance to residents and other non-participating users of recreational areas.
G
Military Sources
Noise from military sources is generally limited to noise from military aircraft and from practice firing ranges. Low-flying aircraft cause considerable disturbance en route from air bases to exercise areas, which are usually remote and often recreational areas (such as the Lake District in England); the noise is likely to startle people as the aircraft fly at high speed and at low altitude. Military helicopters may also exercise in the vicinity of their bases. Practice firing ranges are used for rifle firing, large artillery, tanks, and sometimes by air-toground missiles. Although operations may be fairly limited, the high levels of explosive noise cause a great deal of concern about both noise and vibration in the surrounding communities. Good public relations can help to minimize the adverse impact in these communities.
H
Low-Frequency Sources
A small percentage of the population appears to be highly sensitive to certain types of lowfrequency noise, which is “sensed” rather than heard. In some instances complaints cannot be related to any identifiable source, but on occasions they can be traced to specific sources which may be some distance from the complainant. Once the source is positively identified, it is sometimes possible to reduce the offending noise quite simply. Examples of sources which can produce this type of noise include furnaces, burners, and fans, which might under certain circumstances set up low-frequency resonances within buildings, although these will normally be at low levels.
Contributed By: John G. Walker Microsoft ® Encarta ® Encyclopedia. © 1993-2004 Microsoft Corporation. All rights reserved.
Water Pollution I
INTRODUCTION
Water Pollution, contamination of water by foreign matter such as micro-organisms, chemicals, industrial or other wastes, or sewage. Such matter deteriorates the quality of the water and renders it unfit for its intended uses.
II
MAJOR POLLUTANTS POLLUTANTS
The major pollutants of water are the following: • Sewage and other oxygen-demanding wastes (largely carbonaceous organic material, the decomposition of which leads to oxygen depletion). • Infectious agents. • Plant nutrients that can stimulate the growth of aquatic plants, which then interfere with water uses and, when decaying, deplete the dissolved oxygen and produce disagreeable odours. • Exotic organic chemicals, including pesticides, various industrial products, surface-active substances in detergents, and the decomposition products of other organic compounds. • Petroleum, especially from oil spills. • Inorganic minerals and chemical compounds. • Sediments consisting of soil and mineral particles washed by storms and floodwater from croplands, unprotected soils, mine workings, roads, and bulldozed urban areas. • Radioactive substances from the wastes of uranium and thorium mining and refining, from nuclear power plants, and from the industrial, medical, and scientific use of radioactive materials.
Heat may also be considered a pollutant when increased temperatures in bodies of water result from the discharge of cooling water by factories and power plants.
III
EFFECTS OF WATER POLLUTION
Notable effects of water pollution include those involved in human health. Nitrates (the salts of nitric acid) in drinking water can cause a disease in infants that sometimes results in death. Cadmium in sludge-derived fertilizer can be absorbed by crops; if ingested in sufficient amounts, the metal can cause an acute diarrhoeal disorder and liver and kidney damage. The hazardous nature of inorganic substances such as mercury, arsenic, and lead has long been known or strongly suspected. Lakes are especially vulnerable to pollution. One problem, eutrophication, occurs when lake water becomes artificially enriched with nutrients, causing abnormal plant growth. Run-off of chemical fertilizer from cultivated fields may trigger this. The process of eutrophication can produce aesthetic problems such as bad tastes and odours and unsightly green scums of algae, as well as dense growth of rooted plants, oxygen depletion in the deeper waters and bottom sediments of lakes, and other chemical changes such as precipitation of calcium carbonate in hard waters. Another problem, of growing concern in recent years, is acid rain, which has left many lakes in northern and eastern Europe and north-eastern North America totally devoid of life.
IV
SOURCES SOURCES AND CONTROL
The major sources of water pollution can be classified as municipal, industrial, and agricultural. Municipal Municipal water pollution consists of wastewater from homes and commercial establishments. establishments. For many years, the main goal of municipal sewage disposal was simply to reduce its content of suspended solids, oxygen-demanding materials, dissolved inorganic compounds (particularly compounds of phosphorus and nitrogen), and harmful bacteria. In recent years, however, more stress has been placed on improving the means of disposal of the solid residues from municipal treatment processes. The basic methods of treating municipal wastewater fall into three stages: primary treatment, including grit removal, screening, grinding, flocculation (aggregation of the solids), and sedimentation; secondary treatment, which entails oxidation of dissolved organic matter by means of biologically active sludge, which is then filtered off; and tertiary treatment, in which advanced biological methods of nitrogen removal and chemical and physical methods such as granular filtration and activated carbon adsorption are employed. The handling and disposal of solid residues can account for 25 to 50 per cent of the capital and operational costs of a treatment plant. The characteristics of industrial wastewaters can differ markedly both within and among industries. The impact of industrial discharges depends not only on their collective characteristics, such as biochemical oxygen demand and the amount of suspended solids, but also on their content of specific inorganic and organic substances. Three options (which are not mutually exclusive) are available in controlling industrial wastewater. Control can take place at the point of generation within the plant; wastewater can be pretreated for discharge to municipal treatment treatment systems; or wastewater can be treated completely at the plant and either reused or discharged directly into receiving waters. Agriculture, including commercial livestock and poultry farming, is the source of many organic and inorganic pollutants in surface waters and groundwater. These contaminants include both sediment from the erosion of cropland and compounds of phosphorus and nitrogen that partly originate in animal wastes and commercial fertilizers. Animal wastes are high in oxygendemanding material, nitrogen, and phosphorus, and they often harbour pathogenic organisms. Wastes from commercial feeders are contained and disposed of on land; their main threat to natural waters, therefore, is via run-off and leaching. Control may involve settling basins for liquids, limited biological treatment in aerobic or anaerobic lagoons, and a variety of other methods.
V
MARINE POLLUTION
Wastes that are discharged directly into United States marine waters are estimated conservatively to exceed 45 million tonnes per year. About 80 per cent of this amount is waste produced by dredging, 10 per cent is industrial waste, and 9 per cent is sewage sludge. The presence of toxic substances, the rapid uptake of contaminants by marine organisms, heavy deposits of materials on the bottom environment near the shore, and excessive growth of
undesirable organisms—the combination of all these aspects has very serious consequences. In the United Kingdom, dumping of industrial waste in coastal waters finished at the end of 1992. Of the remaining types of waste dumped at sea, the average annual amount in the period 1981 to 1994 was estimated at 39,676,000 tonnes. Of this, sewage sludge represented 22 per cent, and dredging (mainly from ports and estuaries) 78 per cent (gravel and mud comprising 14 per cent, and sand and silt 64 per cent). The dumping of sewage sludge by the United Kingdom finished in the late 1990s.
VI
OIL SPILLS
Large-scale accidental discharges of liquid petroleum products are an important cause of pollution along shorelines. The most spectacular cases of oil pollution involve the supertankers used for its transport, but many other ships also spill oil, and offshore drilling operations contribute a large share of the pollution. One estimate is that of every million tonnes of oil shipped, one tonne is spilled. Some of the largest spills thus far recorded involve the tanker Amoco Cadiz off Cadiz off the French coast in 1978 (1.6 million barrels of crude oil) and the Ixtoc I oil well in the Gulf of Mexico in 1979 (3.3 million barrels). The spill of 240,000 barrels by the tanker Exxon Valdez in Valdez in Prince William Sound, Gulf of Alaska, in March 1989, caused within a week a 6,700-sq-km (2,600-sq-mi) slick that endangered wildlife and fisheries in the entire gulf area. On the other hand, the spill of 680,000 barrels from the Braer on Braer on the coast of the Shetland Islands in January 1993 was broken up by the wave action of exceptionally severe storms and had mostly dispersed within a few days.
The oil spills in the Persian Gulf in 1983, during the Iran-Iraq conflict, and in 1991, during the Gulf War, when up to 8 million barrels were released, resulted in enormous damage to the entire area, especially to the marine life. See also Environment; Sewage Disposal; Water Supply and Waterworks. Microsoft ® Encarta ® Encyclopedia. © 1993-2004 Microsoft Corporation. All rights reserved.
II
REACTIONS TO NOISE
“Annoyance” tends to be used to describe the general feeling of aggravation or vexation caused by noise nuisance. nuisance. It is the end of the noise/disturbance/annoyance chain. General long-term annoyance is the most convenient and relevant measure of the impact of noise on the community. It takes account of all the adverse effects of noise such as disturbance. Studies have been carried out to examine the relationship between exposure to noise from specific sources (the noise dose) and the annoyance caused (the response). Even though there is a wide variation in the annoyance reactions of individuals, the information can be used to define the “average” dose-response relationship, or the percentage of the population likely to display a specific degree of annoyance to a defined level of noise. When the noise is at a sufficiently high level the opinions may be clear-cut; the noise is the main factor in determining annoyance. At lower levels of noise, the general attitudes of the community as a whole, or of individual members of the community, towards the noise source, may assume greater importance. The degree of annoyance may be influenced by the length of time to which a community or an individual has been exposed to noise, and by the time of occurrence.
A
Sleep Disturbance
Research has shown that many factors affect sleep quality. About 20 per cent of the population have sleeping difficulties which are totally unrelated to noise. Age, sex, attitudes, and health factors override the impact of noise-induced sleep disturbance. Background noise levels, habituation, bedroom location, time of night, and the character of any intruding noise also influence sleep quality. Bearing this in mind, it is unrealistic and often impractical to set noise limits to ensure that sleep will not be affected in any way.
III
DESCRIBING NOISE
The level of environmental noise is normally measured with a Sound Level Meter using the Aweighted decibel scale (dB(A)). The decibel (dB) is the scale which is used to describe the
sound-pressure level of the sound. It is the logarithm of the ratio of the measured sound pressure (which is what the eardrum detects) relative to a reference value, which is a very small sound pressure which automatically acquires the value 0dB. For every ten-fold increase in sound pressure, the sound-pressure level increases by 20dB. The term “A-weighting” means that the signal is filtered in a way that approximates to the frequency sensitivity of the human ear. However, the level of noise originating from a source is not the only consideration affecting its impact; duration is also important. Sometimes the noise is intermittent intermittent (for example, aircraft aircraft or train noise), while sometimes it is more or less continuous (such as motorway or factory noise). So, where separate noise events are clearly distinguishable, the important factors are the maximum level and duration of each event and the number of events in a given period, while continuous noise is averaged in some way over the exposure duration. Different methods have been devised to describe the varying temporal characteristics of different sources, but the most widely used descriptive standard for environmental noise is the Equivalent Continuous Noise Level (LAeq). LAeq describes the noise (in dB(A)) in terms of the A-weighted acoustical energy of the noise averaged over a specific time period, and is defined as the level of continuous noise that would have the same acoustical energy as the actual noise over the same time period. However, equal values of L Aeq for different sources do not necessarily elicit the same community reaction. The different characteristics of the noise, both temporal and spectral, are factors which play an important role in determining response, which cannot be adequately described by a measure of the noise alone. These differences are normally taken into account when defining standards and in noise guidelines such as the UK Planning Policy Guidance PPG 24.
IV
NOISE STANDARDS
It is possible to estimate the proportion of the population exposed to specific environmental noise levels. Taken together with information from studies of dose-response relationships, it is then possible to identify the impact of noise on the community as a whole, in terms of the proportion of the population likely to be adversely affected by noise. This information is essential when planners, lawyers, technical experts, and economists have to define noise targets and goals. The targets, taking costs and benefits into account, may range from “ideal long-term” to “practicably achievable in the shorter term”. These targets, in turn, influence noise emission (source noise level) and immission (environmental noise exposure) standards and legislation, such as the United Kingdom Environmental Protection Act 1990. For example, a report published by Stockholm University for the World Health Organization in 1995 has concluded that noise levels outside dwellings should not exceed 55dB(A) to protect the majority of people from being seriously annoyed, and that 50dB(A) should be considered
the maximum desirable. These levels can be considered as ideal targets, but because of technical, financial, and practical considerations, exposure levels higher than these will remain commonplace in the developed world for some time to come, and noise-exposure standards will be set at higher levels, although efforts will continue to be made to reduce them. International noise-emission standards are designed to control the noise emitted by specific machines, such as aircraft, cars, or industrial equipment. Environmental noise exposure standards and legislation are, on the other hand, normally devised by national or local authorities to provide an acceptable noise environment for their specific conditions. Noise immission levels depend not only on the noise emitted by particular sources, but also the distance from the source, and the use of noise attenuation measures such as noise barriers or double glazing which may be required to meet national or local noise immission standards. In order to ensure that noise levels can be predicted to an acceptable degree of accuracy and in a consistent manner, most countries have published official methods for calculating noise exposure for road traffic, aircraft, railways, and other types of noise source.
V
NOISE IN THE COMMUNITY
The main sources of noise pollution in the community are transport sources such as aircraft taking off and landing, road traffic, and railways; fixed industrial and commercial installations; construction activities; and (increasingly) leisure activities. Noise from neighbours (stereo systems, late-night comings and goings, children, barking dogs) now causes more reported complaints than any other source, but quantifying the offending noise level is often a part of this type of problem, which is more a question of considerate behaviour than noise limits. The noise level is also dependent on the building’s construction and the attenuation it provides between dwellings.
A
Road Traffic
Road traffic noise is the most widespread noise source in developed countries. A study carried out for the European Commission by the French institution INRETS in 1994 estimated that some 200 million people in the European Union (60 per cent of the population) were exposed to levels of road traffic noise exceeding 55dB(A), and some 132 million (39 per cent) to 60dB(A). In order to reduce exposure, noise emission limits have been defined for all new vehicle types. The limits have been progressively lowered lowered over the years, so that the noise emitted by new vehicles at the beginning beginning of the 21st century was some 8 to 10 dB lower than 25 years before. Most of this effort has reduced the noise from car engines and ancillary equipment so much that tyre noise, even on urban roads, is becoming the dominant source, and “quiet” road surfaces are now being used for some new roads, and quieter tyre designs being considered. However, despite these efforts, the report predicted that traffic-noise exposure levels would increase, particularly in the quieter areas, for the subsequent 10 to 20 years because of the growth in the number of vehicles.
B
Railways
Although railways railways are generally seen as the safest, most economical, and most environmentally friendly of all conventional transport systems, many countries are now reappraising the cost of new railways in terms of environmental impact. This has been particularly true with high-speed railways. The latest high-speed trains have been designed to be no noisier than the older and slower conventional trains, but careful planning of new routes and provision of noise abatement procedures are still needed to meet environmental standards. However, trains create a less extensive noise burden than road traffic, so that, overall, the noise environment may improve.
C
Aircraft
Concern about aircraft noise grew rapidly after World War II and, by the mid-1960s, it had reached such a level that aviation authorities and manufacturers realized that noise from the early jet engines needed to be controlled and reduced in order to create a more acceptable environment. The predominant source of noise from both jet and propeller-driven aircraft is the power plant itself. The pressures from environmental lobbies have driven authorities to establish legislation to control aircraft noise by certification and the manufacturers have made great strides to reduce noise from the engines themselves. Noise levels have fallen by about 20dB since the days of the early jet aircraft, which, even though they are now larger and carry more passengers, have become far more fuel-efficient and less noisy. Whereas the early jet engine was dominated by the jet noise and compressor whine, whine, the latest high-bypass high-bypass ratio engine is characterized by fan noise both to the front and rear of the engine and the relatively low level of jet noise. While much of the work which has resulted in lower noise emission levels from jet aircraft was driven by the need to comply with noise certification requirements, public concern about the noise around airports led to the introduction of noise exposure standards or limits which are generally based on LAeq. Noise exposure contours, normally computer generated, are used to give an indication of the likely noise impact at any particular location in the vicinity of an airport. Computer modelling can also be used to evaluate the impact of any changes, such as modifications to arrival or departure routes, or the replacement of older, noisier aircraft with newer, quieter ones. However, it must always be borne in mind that noise exposure contours will never give a precise prediction of community response.
D
Industry
Most manufacturing and industrial operations create noise. In many cases this may be limited to the plant’s interior, while in others it will affect the communities in the neighbourhood. neighbourhood. Although the community noise problem was formerly restricted mainly to heavy manufacturing industry, this is not necessarily the case today, and small manufacturing or service businesses which create noise may be located close to residential properties. The introduction of improved ventilation and heating systems has resulted in the installation of powerful fans located in the walls and roofs of buildings which can, if badly positioned, lead to significant noise levels in the neighbourhood, especially at night.
E
Construction
Construction activities activities are noisy and have the potential to cause disturbance in the surrounding communities. Some sources will generate continuous steady levels (such as fans, extractors, or compressors), some will be intermittent (such as sawing or drilling), while others will be impulsive (such as piling). Environmental noise assessments take the short-term nature of most construction activities into account by allowing higher levels than would normally be considered appropriate for long-term noise exposure.
F
Social Noise
Neighbours make noise; in fact, noise from the living and social habits of our neighbours is generating more complaints than any other single source of noise. Sources include domestic equipment, stereo and TV, animals and children, do-it-yourself activities, and lawn mowers. Many of these complaints may be a consequence of poor insulation insulation between multi-occupier dwellings—which could be improved at the design stage, but not after construction. Unreasonable and antisocial behaviour causes a great deal of noise nuisance, but it is essentially a social rather than an engineering issue. The UK Noise and Statutory Nuisance Act 1993 now provides powers to authorities to seize noisy equipment such as stereo systems if the owner does not comply with an order to reduce the noise level. The growing sophistication of leisure activities over the past few years has led to an increase in noise levels in recreational areas, with an associated increased potential for nuisance to nearby residents and other visitors. Sources include power boats, microlight aircraft, motor cycles, motor racing, clay pigeon shooting, pop concerts, and model aircraft flying. Codes of practice and planning regulations are used by the activity organizers and local authorities in order to minimize the disturbance to residents and other non-participating users of recreational areas.
G
Military Sources
Noise from military sources is generally limited to noise from military aircraft and from practice firing ranges. Low-flying aircraft cause considerable disturbance en route from air bases to exercise areas, which are usually remote and often recreational areas (such as the Lake District in England); the noise is likely to startle people as the aircraft fly at high speed and at low altitude. Military helicopters may also exercise in the vicinity of their bases. Practice firing ranges are used for rifle firing, large artillery, tanks, and sometimes by air-toground missiles. Although operations may be fairly limited, the high levels of explosive noise cause a great deal of concern about both noise and vibration in the surrounding communities. Good public relations can help to minimize the adverse impact in these communities.
H
Low-Frequency Sources
A small percentage of the population appears to be highly sensitive to certain types of lowfrequency noise, which is “sensed” rather than heard. In some instances complaints cannot be related to any identifiable source, but on occasions they can be traced to specific sources which may be some distance from the complainant. Once the source is positively identified, it is sometimes possible to reduce the offending noise quite simply. Examples of sources which can produce this type of noise include furnaces, burners, and fans, which might under certain circumstances set up low-frequency resonances within buildings, although these will normally be at low levels.
