Chemistry environmental chemistry


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Chemistry environmental chemistry

  2. 2. ENVIRONMENTAL CHEMISTRY DEFINTION • Environmental Chemistry is the scientific study of the chemical and biochemical phenomena that occur in natural places. • Environmental chemistry is an interdisciplinary science that includes atmospheric, aquatic and soil chemistry, as well as heavily relying on analytical chemistry and being related to environmental and other areas of science. • Environmental chemistry involves first understanding how the uncontaminated environment works, which chemicals in what concentrations are present naturally, and with what effects. Without this it would be impossible to accurately study the effects humans have on the environment through the release of chemicals.
  3. 3. Environmental pollution   Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light. Tropospheric air pollution has impacts on scales ranging from local to global. Reactive intermediates in the oxidation of mixtures of volatile organic compounds (VOCs) and oxides of nitrogen (NOx) play central roles.
  4. 4. Atmospheric pollution (The atmosphere is divided into five layers) The Troposphere (up to 10 km) It's the atmosphere that surrounds us. The Stratosphere(10-50 km) Very little oxygen or water vapor. Aircraft fly in the lower stratosphere. This is also where the ozone layer exists. The Mesosphere(50-80 km) This is where most meteors burn up, because the density is higher than the outer layers. The Thermosphere(80-650 km) Practically a vacuum. Includes the ionosphere (auroras) as well as space station orbits. The Exosphere(500-2000 km ) The farthest any of Earth's atmosphere exists. Troposphere is a turbulent, dusty zone containing air, much water vapour and clouds. This is a region of strong air movement and cloud formation. The stratosphere, on the other hand, contains dinitrogen, dioxygen, ozone and little water vapour. The presence of ozone in the stratosphere prevents about 99.5per cent of the sun’s harmful ultraviolet (UV) radiations from reaching the earth’s surface and thereby protecting humans and other animals from its effect.
  5. 5. Tropospheric pollution    Tropospheric pollution occurs due to the presence undesirable solids or gaseous particals in the air. The major gaseous and particular pollutants present in troposphere: 1.gaseous air pollutants :these are oxides of sulphur, nitrogen and carbon, hydrogen sulphide, hydrocarbons, ozone and other oxidents. 2.particulate pollutants: these dust, mist, fumes, smoke,smog ,etc.
  6. 6. Gaseous air pollutants a) Oxides of Sulphur b) Oxides of Nitrogen c) Hydrocarbons d) Oxides of Carbon i. Cabon monoxide ii. Cabon dioxide
  7. 7. Global warming and green house effect About 75% of the solar energy reaching the earth is absorbed by the earth’s surface, which increases its temperature. The rest of the heat radiates back to the atmosphere. Some of the heat is trapped by gases such as carbon dioxide, methane, ozone, chlorofluorocarbon compounds (CFCs) and water vapours in the atmosphere. Thus they add to the heating of the atmosphere. This causes global warming. Large amount of methane are released in paddy fields, coal mines, from rotting garbage dumps and by fossil fuels. chlorofluorocarbons (CFCs) are man-made industrial chemicals used in air conditioning etc.CFCs are also damaging the ozone layer. if this trends continue, the average global temperature will increase to a level which may lead to melting of polar ice caps and flooding of low lying areas all over the earth. increase in the global temperature increases the incidence of infectious diseases like dengue, malaria, yellow fever, sleeping sickness etc.
  8. 8. Acid rain We are aware that normally rain water has a pH of 5.6 due to the presence of H+ ions formed by the reaction of rain water with carbon dioxide present in the atmosphere. H 2O (l) + CO2 (g) =H2CO3 (aq) H2CO3 (aq) = H+ (aq) + HCO3- (aq) When the H of the rain water drops below 5.6, it is called acid rain. acid rain refers to the ways in which acid from the atmosphere is deposited on the earth’s surface. Oxides of nitrogen and sulphur which are acidic in nature can be blown by wind along with solid particles in the atmosphere and finally settle down either on the ground as ground deposition or in water, fog and snow as wet deposition. acid rain is a byproduct of a variety of human activities that emit the oxides of sulphur and nitrogen in the atmosphere. SO2 and NO2 after oxidation and reaction with water are major contributors to acid rain, because polluted air usually contains particulate matter that catalyse the oxidation. acid rain is harmful for agriculture, trees and plants as it dissolves and washes away nutrients needed for their growth. It causes respiratory ailments in human beings and animals. it affects plants and animal life in aquatic ecosystem. It corrodes water pipes resulting in the leaching of heavy metals such as iron, lead and copper into the drinking water. Acid rain damages buildings and other structures made of stone or metals. The Tajmahal in India has been affected by acid rain.
  9. 9. Smog The word smog is derived from smoke and fog. Conditions  of Photochemical Smog Formation Photochemical smog happens when nitrogen oxides and volatile organic compounds react together in the presence of sunlight as a catalyst and form ozone at lower levels. The nitrogen oxides are emitted from vehicle exhausts and volatile organic compounds are generated by a multitude of chemicals, such as paint and cleaning agents. The effects of smog on human health and the environment are serious and harmful. The toxic chemicals formed in a photochemical smog can irritate nasal passages and eyes. Breathing problems can become aggravated due to prolonged exposure to smog conditions. Some of the toxins generated by chemical reactions in the photochemical smog are considered carcinogenic. The acidic nature of the smog can also cause environmental damage and structural decay in dwellings.
  10. 10. There are two types of smog: a) classical smog occurs in cool humid climate. It is a mixure of smoke, fog and sulphur dioxide. Chemically it is a reducing mixure and so it is also called a reducing smog. Winter Smog Winter smog is essentially created by the excessive use of fossil fuels to heat up homes and buildings. Winter photochemical smog forms during extreme weather conditions, particularly during the height of winter. This is because during extremely cold conditions, populations of cities which have large number of hearth-heated homes use coal or other combustibles that generate considerable amounts of smoke and pollutants. These air pollutants are emitted at the lower levels in the atmosphere. The cold and moist air retains the emissions for a longer time through the chemical reactions that take place at a slower rate. Cities boxed in by surrounding higher elevations which experience heavy snowfalls face smog regularly. b) Photochemical smog occurs in warm, dry and sunny climate. The main component of the photochemical smog results from the action of sunlight on unsaturated hydrocarbons and nitrogen oxides produced by automobiles and factories.Photochemical smog has high concentration of oxidizing agents and is,therefore,called as oxidizing smog.
  11. 11. Causes of Summer Smog Formation Cities with a geography that does not allow proper dispersal of emissions by wind and helps the smoke get trapped by extreme weather conditions experience summer smog. The abundance of sunlight and high temperatures during the summer speeds up chemical reactions in the atmosphere, which, mingled with humidity, creates dense smog. At times,temperature inversions at higher altitudes lead to the formation of summer photochemical smog by trapping a humid layer of air below a layer of warm air, which holds up the pollutants. Coastal cities surrounded by hills or mountains are prime candidates for summer smog. Effect of photochemical smog The common component of photochemical smog are ozone, nitric oxide, acrolein, formaldehyde and peroxyacetyl nitrate(PAN). Photochemical smog causes seriously health problems. Bothozone and PAN act as powerful eye irritants. Ozone and nitric oxide irritate the nose and throat and their high concentration causes headache, chest pain dryness of the throat, cough and difficulty in breathing. Photochemical smog leads to cracking of rubber and extensive damage to plant life. It also causes corrosion of metals, stones, building materials, rubber and painted surface
  12. 12. Nitrogen Oxides Primary gases in photochemical smog are nitrogen oxides. Nitrogen oxides are a mixture of gases, two of which are significant in the production of photochemical smog. These two are nitric oxide and nitrogen dioxide. Nitrogen oxides come from combustion processes such as the burning of gas in motor vehicles, burning of coal or even forest fires. VOCs VOCs are organic compounds that easily turn to gases and are the result of gasoline exhaust (from cars, trucks, buses and gasoline stations), industrial emissions or paint fumes. They are composed of hydrogen, carbon and other elements such as sulfur and nitrogen. VOCs are sometimes referred to as hydrocarbons. Ozone The type of ozone found in photochemical smog is located in the troposphere, the layer of the atmosphere that is closest to the Earth's surface. This type of ozone is referred to as ground-level ozone and is harmful. Ground-level ozone forms from a chemical reaction involving nitrogen oxides, VOCs and sunlight. When sunlight and hot weather are present, ground-level ozone can reach harmful concentrations if there is no wind. PANs PAN forms as the result of complex chemical reactions between nitric oxide (NO) and VOCs. Scientists began studying PAN as early as the 1940s when plants on farms near Los Angeles began showing ill effects, found to result from the city's onset of smog. Scientists found PAN is 10 to 50 times more toxic than oxone to plants and is a major eye irritant.
  13. 13. Forming Photochemical Smog For photochemical smog to form, several chemical reactions need to take place between nitrogen oxides, VOCs, and sunlight. Although photochemical smog is the result of a series of complex chemical reactions, it can be illustrated by a simple example that starts with heavy traffic during the morning commute. The byproducts of the fuel burning vehicles, nitrogen oxides and VOCs, are emitted in the exhaust fumes coming from the vehicles. The nitrogen oxides and VOCs quickly react to form nitrogen dioxide (NO2). Then, as the day progresses, the sunlight becomes stronger and more intense. The sunlight reacts with the nitrogen dioxide (NO2) to form ground-level ozone. The nitrogen dioxide (NO2) also reacts with VOCs to form PAN. This combination of toxic gases makes up photochemical smog. These chemical reactions are ongoing throughout the day and the photochemical smog, under the right circumstances, increases as the day goes on and can get so bad it can reduce visibility.
  14. 14. Stratospheric Pollution Formation and Breakdown of Ozone The chlorine radicals are the continuously regenerated and cause the breakdown of ozone. Thus, CFCs are transporting agents for continuously generating chlorine radicals into the stratosphere and damaging the ozone layer. The Ozone Hole Depletion of ozone layer commonly known as ozone hole over the south pole. Effects of depletion of the Ozone layer With the depletion of ozone layer, more UV radiation filters into troposphere. UV radiations lead to ageing of skin, cataract, sunburn, skin cancer, killing of many phytoplanktons, damage to fish productivity etc.
  15. 15.  •Water Pollution Causes of Water Pollution 1)Pathogens 2)organic wastes 3)chemical pollutants  International standard for drinking water  The international standard for drinking water are given below and they must be followed. Fluoride:for drinking purposes, water should be tested for fluoride ion concentration. Its deficiency in drinking water is harmful to man and causes diseases such as tooth decay etc. However,F-ion concentration above 2ppm causes brown mottling of teeth.Excess fluoride (over 10ppm) causes harmful effect to teeth n bones; Lead : drinking water gets contaminated with lead when lead pipes are used for transportation of water. The prescribed upper limit concentration of lead in drinking water is about is 50ppb.lead can damage kidney,liver,reproductive system etc. Sulphate: excessive sulphate more then 500ppm in drinking water causes laxative effect ,otherwise at moderate levels it is harmless Nitrate : the maximum limit of nitrate in drinking water is 50ppm.excess nitrate in drinking water can cause disease such as methemoglobinemia(blue baby syndrome) OTHER metAls: the maximum concentration of some common metals Fe - 0.2ppm Mn -0.05ppm Al -0.02ppm Cu -3.0ppm Zn -5.0ppm Cd -0.005ppm           
  16. 16. Soil pollution   India being an agriculture based economy gives high priority to agriculture ,fisheries and livestock development. some insecticides n pesticides for protection of our crops. these insecticides and pesticides and herbicides cause soil pollution. Pesticides :    Prior to world war –II many natural occurring chemicals such as nicotine (by planting tobacco plants in the crop field), where used as pest controlling substance for major crops in agriculture practices During world war –II ,DDTwas found to be of graet use in the control of malaria and other insect borne diseases. therefore ,atter the war,DDT was put to use in agriculture to control the damages caused by insects, rodents, weeds, and various crop diseases how ever, due to adverse effects its use has been banned in India. Pesticides are basically synthetic toxic chemicals with ecological repercussion. Most of the organic toxins are water insoluble and nondegradable. The concentration of toxins in higher animal reach a level which causes serious metabolic and physiological disorders.
  17. 17. Industrial waste   Industrial solid wastes are also sorted out as bio degradable n nondegradable wastes. Bio degradable wastes are generally by cotton mills, food processing units ,paper mills and textile factories. Non degradable wastes are generated by thermal power plants which produce fly ash; integrated iron and steel melting slag. Industries manufacturing aluminium, zinc and copper produce mud and tailings. The disposal of non-degradable industrial solid wastes, if not done by a proper and suitable method, may cause serious threat to the environment. Large quantity of toxic wastes are usually destroyed by controlled incineration, whereas small quantities are burnt along wit factory garbage in open bins.
  18. 18. Strategies to control environment pollution       Waste manegment There are household discards, there are medical, agricultural, industrial and mining wastes. The improper disposal of wastes is one of the major causes of environmental degradation. Collecting and disposal Domestic wastes are collected in small bins, which are then transferred to community bins by private or municipal workers. From these community bins, these are collected and carried to the disposable site. At the site garbage is sorted out and separated into biodegradable and non-degradable materials. Nonbiodegradable materials such as plastic, glass, metal scraps etc. are sent for recycling. Bio-degradable wastes are deposited in land fills and are converted into compost. The waste if not collected in garbage bins, finds its way into the sewers. Some of it is eaten by cattles. Non-biodegradable wastes like polythene bag, metal scraps, etc. choke the sewer cause inconvenience. Polythene bags, if swallowed by cattle can cost their lives also.