Lecture 2 environmental danger for the human
1 Environment exhaustible and inexhaustible natural resources
The concept «environment» includes all natural elements, and also part of nature changed by people activity (settlements, agricultural areas, reservoirs and others). By natural resources we understand objects, conditions and processes, which are used or can be used in manufacturing for sufficing material, scientific and cultural needs of society.
The natural resources are divided into exhaustible and inexhaustible.
Inexhaustible natural resources include space (solar radiation and energy of marine flows and waves) and climatic (wind power and Earth bowels) power resources. Taking into account huge masses of air and water medium of the planet atmospheric air and water resources can be referred to inexhaustible resources too. But such reference is conditional, because chemical structure and physical condition of atmosphere and hydrosphere get changed under people activity influence (anthropogenous influence) what can bring to losses of their biological value and possibilities of using. That makes necessary to execute a complex of works on supporting air and water purity.
Exhaustible resources in turn include renewable and nonrenewable natural resources. The renewable resources can be recreated during their using. The renewing goes at various velocities: formation of 1 cm of humus ground layer takes about 600 years, growing of cut down wood - dozens of years, animals' population – up to 10 years. Thus, the rate of renewed resources using should be in balance with rate of their restoring. Nonrenewable natural resources are those which can't be renewed absolutely or their renewing goes slower than their using. Minerals which using entail over crop refer to such resources. Their protection should consist in economic, rational and complex using so resources will have a minimum loss. Besides, nonrenewable resource is the space people live in
Every year they extract from bowels of the Earth 4 km3 of rock, hundred millions tons of gases, solids and liquids are evolved polluting surroundings. Consequently unequal manufacturing development northern hemisphere has 93.5 % of industrial emissions and southern - only 6.5 %. Wood, fish, fresh water get used up ever more. About 10 % of Earth surface has been occupied by construction of cities, roads, pipelines etc. Hydraulic engineering structures (dam, channels and artificial reservoirs) change the rivers more than natural processes for thousands of years.
2 Protection of the atmospheric air
The main sources of atmospheric air polluting are industrial enterprises, thermoelectric power station, motor transport, air transport and agricultural industry. Every year more than 200,000,000 tons of carbon dioxide, 150,000,000 tons of sulfur oxide, 500,000,000 tons of nitrogen oxides, 500,000,000 tons of various hydrocarbon, 250,000,000 tons of fine-dyspersated aerosols (dusts) and many other substances are evolved in the air.
Among industrial branches ferrous metallurgy is the most polluting surrounding. The ferrous metallurgy plants evolve into atmosphere dust structures manganese, arsenic, phosphorum, antimonies, lead and other metals. Non-ferrous metallurgy has inherent toxic dust substance (structure of lead, arsenic and other) and structures of fluorine. In coal industry the source of atmosphere polluting is burning of substances to form carbon oxides and sulfuric gas. The air emissions of petroleum-refining industry contain carbon, styrene, toluol, acetone and other. Structure of chemical industry emissions varies: carbon dioxide, nitrogen, ammonia oxides, organic substances, chloride and fluoric structures, dust of inorganic productions. Manufacturing of construction materials is followed by significant emissions of dust in atmosphere. The thermoelectric power stations evolve in atmosphere about 30 % of total amount of all industrial harmful emissions. These emissions contain carbon and sulfur dioxides, nitrogen oxides, water vapors and plenty of ashes.
Cars are also dangerous for the environment and people health. Cars exhaust gas is a compound of about 200 substances including oxide and dioxide of carbon, aldehyde and structures of lead.
Atmosphere pollution has negative influence on people, flora, fauna, buildings, transport and climate of the Earth.
Particularly negative influence on the people, flora and fauna induces smog (dense fogs) which contains dust and dangerous gases. Smog usually appears in a big industrial city. Photochemical smog with the relative humidity in air less than 70 % is very dangerous for environment. It is caused by extensive polluting air in cities by gas emissions of chemical industry, and also cars' exhaust gases. Photochemical smog induces an inflammation of mucous envelopes, exacerbation of chronic lungs diseases, kills pets, plants, and makes metals corrosion and cloth damage. Bad visibility causes road accidents.
Growing of dust contents in the air results in microclimate deterioration: foggy days are more often, visibility and light exposure decrease. Carbon dioxides contents growing produces greenhouse effect» - essential temperature increasing of Earth surface and surface layer of air owing to decreasing of heat radiation from the Earth.
Protection of air is regulated by limits of acceptable concentration (LAC) of harmful substances in the air of settlements. LAC of harmful substances in atmospheric air covers 200 substances. The hygienic standards are set for more than 600 substances and 33 combinations of atmospheric polluters. Each substance polluting atmospheric air has two norms set: maximum onetime and daily average LAC. Maximum onetime LAC is for preventing reflex reactions (smell sensation, changes of brain activity etc) under short-time (up to 20 min) influence of atmospheric polluters, but daily average one has the purpose to prevent total toxic influence.
The protection of surroundings is achieved by purification of industrial emissions, reducing exhausted gas, selecting sanitary -protective zones and applying wasteless productions.
Purification of emissions from dust can be coarse (when the coarse-dispersed dust with size of particles over 50 micron is intercepted), medium (when the medium-dispersed dust from 10 up to 50 micron is intercepted) and thin (when the fine-dispersed dust under 10 micron is intercepted). For purification from dust there're dust catchers applied which can be divided into two groups -catching dry dust («dry» devices) and scrubber where dust is intercepted after humidifying («wet» devices). «Dry» devices are more applicable and, besides, allow returning an intercepted dust into manufacturing.
The main types of devices for dry purification include cyclone separators, fabric filters and electrofilters.
The emissions purification from gases is achieved by using adsorption and absorption methods.
Absorption methods are based on removing harmful impurities by the liquid. Contact of gases with the liquid is carried out in special means «absorbers», gas and liquid move contraflow in which. Basically absorption process is not just a process of gas dissolution in the liquid, but chemical interaction between dangerous substances being in gases and components absorbing solution. Absorption methods are simple, reliable and have high degree of purification, however their using has some difficulties connected with applying of cumbersome equipment and salvaging of worked out solutions.
Adsorption methods for purification are based on taking up of impurities by a surface of rigid bodies (adsorbents). The important feature of adsorption is that the process passes without changing chemical structure of adsorbed substances and adsorbent. That allows to return adsorbed gases into manufacturing and multiply use an adsorbent.
For some industry (for example, thermoelectric power station, metallurgical works etc) building filter-catchers and smoke stacks is effective enough. Smoke stacks allow to carry off combustion product (harmful gases and rigid particles) in the upper layers of atmosphere and spread them on large territories. For example, the smoke stack with 100 m of height lets spread harmful substances around in radius of 20 km in safe concentration, and when its height is 250 m radius of spreading is increased to 75 km.
For atmospheric air protection from motor transport emissions using of neutralizers of exhaust gases is recommend, which catch carbon oxide and hydrocarbon; using of diesel fuel exhaust gases of which don't almost contain carbon oxide and structures of lead; using of compressed gas; regulating of city traffic intensity and bridge constructing.
Industry or its separate structures with technological processes, which are sources of air polluting with harmful substances and ones having bad smell, are separated from living buildings by sanitary-protective zones (wood or ground spaces which border factories and living arrays). The size of sanitary-protective zones depends on class of the factory (I th class needs 1000 m, 5th class - 50 m). Within the sanitary – protective zones construction of sports structures, parks, children establishments, schools and other is restricted.
Most effective measure on protection of atmospheric air is creation and introduction of wasteless technologies. First of all it concerns the metallurgical and chemical works. As Louis Button said: «we've got two choices: either people make less smoke in the air, or the smoke will make less people on the Earth».