PollutionPosted by Encyclios on May 17, 2023 at 3:53 PM
Pollution is an alteration of the environment, natural or due to anthropization, by pollutants. It produces temporary discomfort, pathology or permanent damage to life in a given area, and can put the area in disequilibrium with existing natural cycles. Alteration can be of different origins, chemical or physical. Pollution is direct, when pollutants are produced by human activity; indirect, when it is due to modifications of primary pollutants that occur under particular environmental conditions.
The pollutants released into the biosphere are mostly produced by human activity in its various forms: biological (organic waste), domestic (heating and garbage), industrial (in particular the chemical, petrochemical, paper, metallurgical and energy sectors), agricultural (manure, artificial fertilizers, pesticides), and transport (especially road transport). For some substances (those called non-biodegradable) degradation may take a long time or not occur at all: these, accumulating in biogeochemical cycles and food chains, give rise to the so-called “biological magnification”; their excessive accumulation has a polluting effect when the amount released into the environment exceeds the possibility of degradation and dispersion.
Instead, inorganic substances, such as metals, hydrocarbons, asbestos, chlorofluorohydrocarbons, chlorides, oxidizing compounds, exert a toxic action on humans, animals, plants and the environment as a whole. Often the products that are released are more toxic and wider range of action of the original pollutants: so, for example, the catalytic effect of ultraviolet radiation from sunlight on nitrogen oxides and unsaturated hydrocarbons, present in emissions from refineries and motor vehicle exhaust gases, form peroxides, such as peroxyacetylnitrate and ozone, which constitute the so-called photochemical smog that has harmful effects on both humans and vegetation.Encyclios replied 3 weeks, 2 days ago 1 Member · 6 Replies
EncycliosOrganizerMay 17, 2023 at 3:54 PM
The main culprits of air pollution are vehicles with internal combustion engines, industries, thermoelectric power plants, domestic heating, waste incineration plants, especially if they do not have suitable dust abatement and smoke purification systems.
Among the main pollutants are mentioned: Smoke, soot, ash, and dust emitted from heating systems, factory chimneys, waste incineration plants, cement plants, quarries, and mines; gaseous sulfur compounds, in particular sulfur dioxide, chosen as a parameter for assessing the degree of atmospheric pollution (which comes from the combustion of fossil coal, especially of poor or mediocre quality, of coke and heavy fuel oils, from the production of sulfuric acid, from the processing of many plastics, from the roasting of pyrites, from the desulfurization of natural gases), hydrogen sulfide (due to the desulfurization processes of petroleum in general and of gasoline in particular and of natural gases) and the malevolent thiophenes and mercaptans emitted by refineries and coke ovens; carbon monoxide, the most widespread gaseous pollutant that derives from the incomplete combustion of substances containing carbon, above all coal and hydrocarbons, while complete combustion forms carbon dioxide; nitrogen oxides, present in the exhaust gases of motor vehicles or due to the production of nitric acid and nitrates; hydrocarbons, unburnt or pyroscopic, present in the exhaust gases of motor vehicles; ozone, present in photochemical smog, around high-voltage electrical systems, and in the exhaust gases of idling internal combustion engines; lead in various volatile forms, released from the exhaust gases of motor vehicles fueled with ethylated gasoline, i.e., containing tetraethyl lead as an antiknock additive; various inorganic and organic acids (sulfuric, hydrochloric, hydrofluoric, bromidic, acetic, fumaric, tannic, etc.) released in combustions or from the manufacture of nitric acid and nitrates; and lead in various volatile forms, released from the exhaust gases of motor vehicles fueled with ethylated gasoline, i.e., containing tetraethyl lead as an antiknock additive.
Artificial radioactive products due, in addition to atomic explosions, to the processing of radioactive substances for the peaceful use of nuclear energy, to the use of radioactive nuclides in scientific research, industry, medicine and agriculture. To these man-made pollutants are added the normal natural atmospheric impurities such as pollen, spores, windblown dust, cosmic dust, volcanic ash or produced by forest fires, salt particles released from the sea surface, etc..
Unfortunately, the consequences of air pollution are hardly susceptible to timely control and are very often referred to different causes. Long-term high pollution levels, which often result in collective intoxication, often have catastrophic consequences on entire ecosystems. In particular, for humans and vertebrates, hydrocarbons have been shown to be potent carcinogens, promoting, among other things, the onset of lung cancer. Moreover, together with carbon monoxide and tetraethyl lead, they contribute, at a cellular level, to the enzymatic block of the respiratory chain.
As for the photochemical smog mentioned above, in addition to irritating and toxic effects on humans (eyes and respiratory tracts), it causes particularly serious damage to vegetation. The peroxyacetylnitrate is in fact responsible for the enzymatic block of photosynthesis and ozone, by enhancing the respiration of plants, causes an abnormal depletion of their nutrients; particularly insidious are also various gases and industrial exhaust fumes (such as solvents), as, at levels already toxic to the body, are not easily perceived by the senses.
Particularly alarming is finally the pollution of the atmosphere by radioactive products. Radionuclides, constituting the so-called fallout, are deposited on the ground, thanks also to atmospheric precipitations, and become part of the ecosystem food chain. It is believed that environments poorly supplied with nutrients more easily absorb radioactive nuclides; the latter, entering the biogeochemical cycles, are fixed by plants and from there pass, concentrating in tissues, to primary and secondary consumers, and so on, up to man with all the consequences that follow. It has been proved, for example, that some radioactive constituents of fallout (strontium 90 and cesium 137), absorbed by soil (concentration factor=1) and fixed by vegetation (concentration factor=21), are then found accumulated in high doses (concentration factor=714) in the bone tissue of herbivores such as sheep, deer, reindeer, thus constituting a danger for human populations consuming milk and meat of these animals.
Air pollution is measured by measuring the concentration of the main pollutants in special measuring stations, located so as not to be directly influenced by emissions from industrial areas or large urban agglomerations; the values measured are compared both with the maximum admissible values and with those of the “background concentration” measured in stations located at very high altitudes and far from the sources of pollution, according to OECD (Organisation for Economic Cooperation and Development) suggestions. The values measured in these stations, besides being very low, are almost constant. Other monitoring stations are installed in various points of the cities, where the concentration of pollutants produced by motor vehicles and combustion processes (SO2, CO2, NO2, O3) is very high. This concentration is often accentuated by particular conditions, such as the absence of wind and rain and thermal inversion.
Two alert levels are usually established, which should be matched by measures to bring the values within the established limits. Air pollution can be reduced by improving the quality of fuels (desulphurization); promoting the use of “clean” fuels (methane) and reducing dust and soot contained in the exhaust gases of thermal plants, before releasing them into the atmosphere; improving the thermal insulation of buildings, to reduce the amount of heat required; using district heating and cogeneration plants (combined production of electricity and heat) that allow a more effective control of polluting emissions. With regard to pollution produced by circulation, there is a tendency to reduce urban traffic by promoting the use of public transport; the amount of tetraethyl lead added to petrol as an anti-knock agent has been reduced, pending its complete elimination.
As long as industry was non-existent, or in an embryonic state, as long as chemical detergents and fertilizers did not exist and as long as urban agglomerations were far from their current size, the self-purification processes of water and soil were sufficient to avoid water pollution. The increase in population, industrial development and the widespread use of chemicals in all human activities have caused a significant increase in the amount of sewage and a radical change in its composition: it is no longer organic substances easily biodegradable, but a mixture of organic and inorganic substances, some of which are very harmful and extremely difficult to eliminate.
Inland waters are polluted by industrial, agricultural and urban discharges. The pollutants diffused in industrial effluents are mainly chemical compounds in solution or in the form of emulsion and foams: strong acids and bases, mineral salts (particularly of chromium, zinc, cadmium, copper, nickel, lead, ammonia salts and also chlorides, fluorides, sulfides, cyanides, sulfites and hydrosulfites), hydrocarbons, tar, vegetable oils and fats, phenols, starches and sugars, dyes, etc.. There are also solid materials of various sizes and of organic or mineral nature (colloids, residues of wood and paper processing, waste and residues of the food industry, sands, crushed stone, etc.) and radioisotopes.
In urban effluents, on the other hand, putrescible organic substances more or less contaminated by pathogenic and parasitic microbial forms, and foams from detergents and soaps prevail. Agricultural effluents mainly contribute nutrients and biocides by leaching fertilizers and pesticides from the fields.
Marine pollution results not only from polluted inland water runoff, but also from the direct discharge operated, without effective purification, by coastal industries and urban settlements and from the disposal of waste by all types of vessels. It should also be taken into account that most of the atmospheric pollutants end up sooner or later in the sea. The sea is seriously contaminated even at a considerable distance from the coasts; the most widespread pollutant is oil because of the criminal practice of discharging tankers into the sea, the repetition of accidents and shipwrecks involving oil tankers, the extraction of oil from continental platforms.
A form of water pollution destined to spread more and more is the thermal one, largely due to the increasing use of water in industrial cooling processes, especially in thermoelectric and nuclear power plants, but no less serious are the effects of thermal discharges from steel mills, sugar refineries, aluminum factories and, in general, of all the many industrial processes that require, at the end of processing, the disposal of residual heat.
The increase in water temperature has, as a first effect, the decrease in the solubility of oxygen, also accelerates all the processes of development of aquatic life, accentuating the phenomena of eutrophy. Along the course of the rivers, thermal dams can be formed, which prevent the ascent of fish. The most serious effects of thermal pollution are, however, due to sudden drops in temperature that cause, in animals now adapted to a warmer environment, the so-called “cold stress”, which can even be fatal; these phenomena are common downstream of power plants when production activity is suspended.
Pollution of natural waters, both marine and inland, has a fairly complex genesis. The presence of sufficient dissolved oxygen is essential for the life of aquatic biocoenosis; if organic substances are introduced into the water in large doses, they are broken down by aerobic bacteria and transformed into simpler substances through the use of a certain part of dissolved oxygen; If pollutants are released in higher concentrations, the aerobic bacteria will consume all the oxygen dissolved in the water and the oxygen absorbed from the external environment; then an anaerobic bacterial population will be established, indifferent to the absence of oxygen and able to break down organic compounds, transforming them into harmful substances, lethal for the life of aquatic plant and animal biocoenosis. Even the discharge of toxic compounds and industrial waste is fatal to aquatic organisms: 0.14 mg/l of copper sulfate are already sufficient to kill a trout for asphyxiation at the gill level, sulfides, cyanides and ammonia instead determine the asphyxiation in the bloodstream and cells in general.
Detergents, which often cover entire water surfaces with a thick foamy layer, due to their complex chemical structure with branched chains, are hardly attacked and degraded by bacteria into simpler and less harmful compounds; these substances therefore strongly alter the physical characteristics of water, modifying its surface tension and causing the disappearance, among other things, of aquatic flora, plankton and, with them, the components of the entire trophic pyramid. This causes, in addition to the extension of large surface layers of decaying matter, with its miasma and various colors, the spread of bacteria and viruses (typhoid, dysentery, cholera, viral hepatitis, etc.) in both fresh and marine waters and the absorption of these pathogenic microorganisms by shellfish for food (such as mussels, oysters and other edible lamellibranchs) and bred near outlets of drains with the consequent danger of serious epidemics.
The superficial layers of oil and other hydrocarbons constitute real impermeable barriers between air and water, preventing the dissolution of atmospheric oxygen in the liquid environment and causing the death by asphyxiation of the entire underwater ecosystem. These substances also damage the beaches, the coastal vegetation and the surface aquatic fauna: sea birds, for example, which, entangled in the dense oily layers, often die from insufficient body thermoregulation and from poisoning.
Another form of pollution of sea water is constituted by the formation of mucilage. More serious, however, is the pollution that occurs in lake basins in which the mixing between hypolimnion and epilimnion and the water exchange are rather slow. Although lakes are relatively more resistant to pollution than rivers, if they exceed a certain limit, the consequences last for decades after the complete cessation of polluting discharges.
Soil and subsoil pollution is caused mainly by the accumulation of solid and liquid waste produced by domestic and industrial activities and by the not always wise use of fertilizers and pesticides in agricultural activities. With regard to municipal solid waste, one can distinguish between rapidly decomposing putrescible organic waste, which is dangerous because it encourages the proliferation of insects and rodents, vectors of disease, and those that are not or slowly biodegradable, such as plastics, wood, paper, metal compounds, gangs, demolition materials, etc.
Industrial discharges directly into the ground can lead, if the soil is not impermeable, to the contamination of groundwater and affect its potability. The massive use of fertilizers promotes, through soil leaching, conditions of water eutrophication. Moreover, chemical fertilizers contain as impurities traces of toxic substances (arsenic, cadmium, lead, copper) that accumulate in the soil; in addition to altering the natural balance, they can pass into the edible parts of plants, which can thus become dangerous to health.
Pesticides also cause serious interference in ecosystems. These toxic substances (DDT and similar) are found concentrated in the organisms of Vertebrates and Invertebrates, after having passed through all the stages of the food chain, from plants to consumers. The case of the increasing rarefaction of birds of prey will serve as an example, in whose organism a very high concentration of pesticides taken with food and responsible for the complete sterility of these animals has been detected.
Noise pollution is a particular form of pollution that affects mainly large cities, some industries and particular activities (e.g. airports). The study of its effects on humans and the environment is only beginning: the alarm raised by the acquisitions on the pathology of noise is very high. Investigations are in progress also on the ecological level, as intense noise sources act negatively on local fauna, not only inducing it to move away, but also causing physiological and, probably, genetic damages. Moreover, the frequency and intensity of diffused sounds seem to affect also the growth and development of plants and, probably, of microfauna, at least in those non-urbanized areas where industrial centers are installed, whose equipment is particularly noisy and so far lacking of effective sound insulation and anti-vibration devices.
Therefore, large industries have shown considerable interest in new systems for absorbing and containing the noise produced by machines and plants; moreover, the use of automatisms and robots has allowed operators to move away from high noise areas (and, in general, from the points where the presence of factors harmful to health is greatest). The problem of noise pollution in cities is still almost completely unsolved: it is hoped to reduce it by building new metro lines (both subway and level, but on rubber wheels) and discouraging, in various ways, the use of private cars in the areas of greatest traffic. As for airports, new aircraft designs aim not only to reduce operating costs, but also to reduce noise levels at takeoff; moreover, the use of airports closer to densely populated areas is already prohibited for the noisiest aircraft.
Effects of weathering on pollution
Concentrations of pollutants in the air depend not only on the number and intensity of pollution sources and the distance from these sources, but especially on local meteorological conditions (for local-scale pollution phenomena) and local and large-scale meteorological conditions (for pollution phenomena at large distances from the sources). For local-scale pollution phenomena, the greatest influence on the transport and atmospheric diffusion of pollutants is due to wind intensity, turbulence conditions (mechanical and thermodynamic) of the lower atmospheric layers, and particular meteorological effects such as breezes (sea or mountain), wind channelling in narrow valleys, or in roads in urban areas, etc.
For large-scale pollution phenomena, the greatest influence on pollutant transport and diffusion is due to wind variations with altitude (wind shear), barotropic or baroclinic conditions in the atmosphere, and large-scale turbulence determined by cyclonic and anticyclonic areas. In general, with the same emission of pollutants from sources, concentrations in small-scale air (urban areas, industrial areas, etc..) are lower when the wind is moderate or strong and the atmosphere is unstable in the lower layers, or when the wind is weak or absent but there is strong insolation with clear skies and sun high on the horizon. Vice versa, concentrations become high when there is inversion of the vertical thermal gradient or in conditions of high pressure at night and with weak wind, or in conditions of persistent fog that causes processes of accumulation of pollutants in the air, sometimes very dangerous for human health.
Effects of pollution on climate
The increase in the carbon dioxide content in the troposphere, as a consequence of the increase in fuel consumption and of the deforestation carried out to make room for new agricultural areas, is not insignificant, having passed, in the space of a century, from 290 to 320 ppm (parts per million) and predicted for the first decade of the XXI century with values between 375 and 400 ppm. Since it is above all the presence, even if on the whole modest, of carbon dioxide and water vapor in the troposphere that, retaining most of the flow of thermal energy radiated from the ground as a result of the phenomenon known as the greenhouse effect, regulates the temperature of the globe, a significant change in the percentage of carbon dioxide can not fail to have climatic repercussions.
For this reason, the increase of carbon dioxide in the atmosphere has been linked to the increase of the average world temperature during the hundred years before 1940. Since then, however, although carbon dioxide continues to be introduced into the atmosphere in increasing quantities, the average world temperature has shown a slight decrease that is interpreted as a consequence of the increased reflectivity, or albedo, of the Earth, due to the intensification of atmospheric cloudiness by fumes and dust produced by industrial and agricultural activities and volcanic eruptions particularly rich in dust (for example that of Pinatubo, in the Philippines, in 1991).
It must be remembered that the particles of smoke and dust, acting as condensation nuclei for water vapor, favor the formation of clouds that further increase the albedo. The effects of atmospheric turbidity are manifested especially in the lower layers and especially in highly industrialized areas with a significant reduction in visibility and increase in haze, fog, cloudiness and precipitation, to the point that industrial cities have more cloudy and rainy days than the surrounding countryside.
Because of the conflicting effects of increased carbon dioxide content on the one hand and cloudiness and turbidity on the other, and also because of the incomplete knowledge of the role of the many geophysical phenomena that intervene in the Earth’s radiation budget, it is impossible to establish with certainty the long-term consequences of these human-induced changes on the atmosphere.
Another consequence of pollution, with effects on climate assessed by scientists in a controversial way, is the accumulation of waste heat released into the atmosphere by various heat-producing activities: for some, the amount of heat administered to the environment is already greater than that disposable by irradiation in space and therefore the temperature is destined to rise with profound alteration of the climate within a few decades, for others the increase in heat can be compensated by activities that raise the albedo such as the expansion of concrete and asphalt surfaces in urban areas or the extension of deserts.
Ultimately, not much is known about the complex mechanism of interactions that regulate the physical environment and the extent of climate interference produced by atmospheric pollutants. Only the systematic monitoring of the dispersion and transport of pollutants, of the variations in the values of atmospheric turbidity, carbon dioxide and water vapor, and ultimately of everything that has an effect on the albedo, conducted on a global scale with the help of suitable meteorological satellites, will be able to provide more precise indications on the actual extent of the alteration of the physical environment.