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Smog …

Atmospheric pollutants
Atmospheric Chemistry

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  • 1. Dr.Henry Antoine Des Voeux Prashant Mehta Assistant Professor National Law University, Jodhpur
  • 2. SMOG • Majority of this pollution was created from the burning of coal for energy generation, space heating, cooking, and transportation. Under the right conditions, the smoke and sulfur dioxide produced from the burning of coal can combine with fog to create industrial smog. In high concentrations, industrial smog can be extremely toxic to humans and other living organisms. Example: London Smog • The use of other fossil fuels, nuclear power, and hydroelectricity instead of coal has greatly reduced the occurrence of industrial smog. However, the burning of fossil fuels like gasoline can create another atmospheric pollution problem known as photochemical smog. Photochemical smog is a condition that develops when primary pollutants (oxides of nitrogen and volatile organic compounds created from fossil fuel combustion) interact under the influence of sunlight to produce a mixture of hundreds of different and hazardous chemicals known as secondary pollutants. Example: LA Smog
  • 3. PHOTOCHEMICAL SMOG To begin the chemical process of photochemical smog development the following conditions must occur: – Sunlight. – The production of oxides of nitrogen (NOx). – The production of volatile organic compounds (VOCs). – Temperatures greater than 18 degrees Celsius. If the above criteria are met, several reactions will occur producing the toxic chemical constituents of photochemical smog.
  • 4. REACTIONS • Nitrogen dioxide can be formed by one of the following reactions. Notice that the nitrogen oxide (NO) acts to remove ozone (O3) from the atmosphere and this mechanism occurs naturally in an unpolluted atmosphere. O3 + NO »»» NO2 + O2 NO + RO2 »»» NO2 + other products • Sunlight can break down nitrogen dioxide (NO2) back into nitrogen oxide (NO). NO2 + sunlight »»» NO + O • The atomic oxygen (O) formed in the above reaction then reacts with one of the abundant oxygen molecules (which makes up 20.94 % of the atmosphere) producing ozone (O3). O + O2 »»» O3 • Nitrogen dioxide (NO2) can also react with radicals produced from volatile organic compounds in a series of reactions to form toxic products such as peroxyacetyl nitrates (PAN). NO2 + R »»» products such as PAN • It should be noted that ozone can be produced naturally in an unpolluted atmosphere. However, it is consumed by nitrogen oxide as illustrated in the first reaction. The introduction of volatile organic compounds results in an alternative pathway for the nitrogen oxide, still forming nitrogen dioxide but not consuming the ozone, and therefore ozone concentrations can be elevated to toxic levels.
  • 5. TOPOGRAPHY Topography • Very important for formation of photochemical smog • Restriction of air movement, city in valley experience more smog problem, than plains
  • 6. METEROLOGY Temperature Inversion • Increase of air temperature with height for some distance above ground causing the smog trapped close to ground • Consequences – Air becomes still and dust and pollutants are no longer lifted from surface • Serious problem in many cities
  • 7. SMOG EFFECTS • Smog can irritate and inflame pulmonary membranes, causing chest pains, coughing, and throat irritation. • Other illnesses such as colds and pneumonia can also be brought on by exposure to smog. • People with asthma problems are under an even greater threat. Even minor exposure to smog may cause these people to get asthma attacks. • Smog slowly ruins people's lungs to an extent as great as that of cigarettes.
  • 8. ACID RAIN • Unpolluted rainwater is slightly acidic (pH 5.6) because of the carbon dioxide from air dissolved in it. CO2 + H2O  H2CO3 • Rainwater with a pH as low as 5.6 to 2.5 has been recorded in some parts of the world. They are commonly known as acid rain. • "Acid rain" is also a broad term used to describe several ways that acids fall out of the atmosphere. A more precise term is acid deposition, which has two parts: wet and dry. – Wet deposition: acidic rain, fog, and snow. – Dry deposition: acidic gases and particles
  • 9. CAUSES OF ACID RAIN • Sulphur dioxide (SO2) and nitrogen oxides (NOx) are the primary causes of acid rain. • Acid rain occurs when these gases react in the atmosphere with water, oxygen, and other chemicals to form various acidic compounds. • Sunlight increases the rate of most of these reactions. The result is a mild solution of sulfuric acid and nitric acid.
  • 10. Formation of Sulphuric Acid (H2SO4) • Sulphur dioxide (from the burning of fossil fuels in power plants and industrial plants) is the primary cause of acid rain. • In the atmosphere, sulphur dioxide is slowly oxidized to sulphur trioxide which dissolves readily in water droplets to form sulphuric (vi) acid. 2SO2+O2  2SO3 SO3 + H2O  H2SO4 • The actual pathways are more complex. • The formation of SO3 from SO2 is influenced by the prevailing atmospheric conditions: sunlight, temperature, humidity, and the presence of hydrocarbons, nitrogen oxides and particulates in the atmosphere. • Sulphuric (iv) acid is also formed when SO2 dissolves in rainwater: SO2 + H2O  H2SO3
  • 11. Formation of Nitric Acid (HNO3) • Nitrogen oxides (from the burning of fossil fuels in automobiles and power plants) also cause the formation of acid rain. • When released to the atmosphere, nitrogen monoxide combines with atmospheric oxygen to form nitrogen dioxide: 2NO + O2  2NO2 • In a series of complex reaction, nitrogen dioxide combines with oxygen and water vapour to form nitric (v) acid. 4NO2 + 2H2O + O2  4HNO3
  • 12. Environmental Problems (i) In water of pH less than 4.5, calcium metabolism in fresh water fish will be affected, leading to poor health and stunted growth. As a result, diversity and population of some fresh water species will be reduced. (ii) In soil of pH less than 4.5, absorption of cations by plants will be affected, resulting in death of plants. (iii) Inflow of acidic water containing poisonous metal ions from soil will kill the fish and water plants (iv) Acid rain corrodes metals and accelerates the deterioration of building, rock and statue.