Air Pollution 1.What is air pollution? 2.Sources of air pollutants 3.Air pollutants 4.Ozone and CFC 5. Photo chemical smog 6.Acid rain 7.Ways to reduce air pollution

What is air pollution?? - the presence of undesirable substances in air at a level that is high enough to cause damage to our health or properties

Sources of air pollutants human activities  burning of fossil fuel  use of motor vehicles  electric power station  factories  incinerators

Burning of fossil fuels causes air pollutions  incomplete combustion of fuels formation of C (soot, smoke), CO & and unburnt hydrocarbon  burning of sulphur containing fuel giving SO  S + O  > SO   combustion at high tempeature formation of NO & NO  from air N  +O  > 2NO 2NO+O  -----> NO 

 combustion of leaded petrol forming lead and PbO  burning of coal with some metal compounds giving ash e.g. soot

Air pollutants 1.Carbon monoxide 2.Nitrogen oxide 3.sulphur dioxide 4.lead compounds 5.unburned hydrocarbons 6.particulates

1.carbon monoxide Nature and Sources of the Pollutant: --Carbon monoxide is a colorless, odorless, poisonous gas formed when carbon in fuels is not burned completely. e.g.C8H18 + 9O2 3CO2 + 3CO +2C +9H2O

Health and Environmental Effects: --Carbon monoxide enters the bloodstream and reduces oxygen delivery to the body's organs and tissues. -Low conc. : causes dizziness,headache, -High conc. :cause unconsciousness and even death

2.nitrogen oxides Nature and Sources of the Pollutant: -Combustion of fuels in high temperature N 2 +O 2 NO 2 --Car exhaust,factories,power stations

Health and Environmental Effects: Irritate and attack respiratory tracts and the lungs Form acid rain

3.sulphur dioxide Nature and Sources of the Pollutant: Burning of fuel which contain sulphur (impurities) -From factories,power station and incineration.

Health and Environmental effects: Harmful respiratory system Cause cancer and heart problems Irritate the eyes Causes acid rain

4.lead cpds. Nature and Sources of the Pollutant: -Combustion of fuel of cars. -lead are added to increase the burning efficiency

Health and Environmental Effects: Lung diseases Affects cell and body processes e.g.CNS,heart attract and hypertension Lack of concentration and memory

5.unburned hydrocarbons Nature and Sources of the Pollutant: -evaporation of petrol -exhaust of incompletely burnt of fuel(factories,power plants)

Health and Environmental Effects: Causing cancer Formation of photochemical smog

6.carbon particulates Nature and Sources of the Pollutant: -incomplete combustion of fuel -car exhaust and power plants

Health and Environmental Effects: Suspended particulates cause lung cancer and diseases such as tuberculosis

Ozone and CFC Formation of ozone 1. Reaction between NO2 and hydrocarbon 2. From air by electrical sparks( in car engine) & in electric machine(photo copier) 3. From atmospheric O2 by absorption of UV radiation O2  O + O O + O2  O3 O3  O2 + O (dissociation of O3)

 it is very important as the screening effect of ozone prevents the harmful UV rays from reaching the earth crust. * 1 & 2 are formed in lower atm., but 3 is in upper atm.

Properties of ozone 1. pale blue gas 2. pungent smell 3. harmless at low concentration 4. causes breathing problems & headache (if conc. >100 ppm) Why do we need ozone? It can filter out 99% if the dangerous UV radiation from the sun. Thus, stop skin cancer, eye contract and crop-yield reduction

Properties of CFC 1. chemically unreactive 2. low flammability 3. highly volatile 4. low toxicity Uses of CFC 1. Aerosol propellants eg trichlorofluromethan(CCl3F), dichlorodifluromethane(CCl2F2) Since CFC is very volatile, it can produce high pressure to propel out eg insecticide

2. Solvents in cleaning agents for electronic component eg tricholorotrifluro ethane ( CCl2F-CClF2 ) CFC can dissolve grease & be removed by evaporation 3. Refrigerants eg Freon( CCl2F2) It is highly volatile that it absorbs heat of vaporization during evaporation => cooling of surrounding

4. Blowing agents in foam plastic manufacturing eg CCl3F CFC is incorporated into monomers. It is then vaporized by the heat evolved during polymerization. Tiny bubbles in plastic formed. Why does CFC accumulate in stratosphere? Since CFC is easily transported, Cl radicals are formed, CFC is insoluble in water,CFC accumulates.

How CFC affect ozone concentration. During last 30 years, there is a drastic change in ozone concentration in stratosphere above Antarctica & Arctic region. Ozone is related to the release of CFCs to the atm. CCl3F + UV rays  CCl2F* + Cl * CCl2F2 + UV rays  CClF2* + Cl* Cl* + O3  ClO* +O2 ClO* + O3  Cl* + 2O2

Controlling the ozone depletion problem 1. restricting the import 2. installing recovery unit and recycling units 3. using substitutes for CFCs a. HCFCs – lower % mass of Cl - break down more quickly in atm - if overuse  still form Cl* b. HFC – no Cl atom  ozone safe - it is toxic

c. hydrocarbon (propane & butane) - no Cl  ozone safe - cheap & readily available - flmmable and poisonous  can’t be widely used d. water & steam - effective in some cleaning application ( vaporizing grease at high temperature)

Photochemical Smog a mixture of pollutants including particulates, NO2, peroxyacetyl nitrate( PAN), ozone, aldehydes, unreacted hydrocarbons,etc. Detecting photochemical smog  Brownish haze & painful eyes ---- brown colour is due to NO haze is due to particulates & droplets ---- pain felt is due to NO2, ozone & PAN

Factors leading to the formation of photochemical smog  reactants : unburnt hydrocarbons & NO2  initiating condition : UV rays  catalyst : particulates & other atmospheric pollutants  climatic factor : absence of strong winds will slow down the disappearance of smog  topographical factor : tall buildings will reduce the air flow in a crowded city

Formation of photochemical smog  Homolysis of NO2 : NO > NO + ‧ O  O atoms react with other components & pollutants of air: O + O > O3 O + hydrocarbons > aldehydes O3 + hydrocarbons > aldehydes Hydrocarbons + O2 + NO > lachrymatory substances ( including PAN )

Effect on human health  causes irritation in mucous membranes ( eyes, noses,throat )  weakens lung functions e.g. coughing, wheezing Effects on organic materials  deteriorates rubber worn out easily  deteriorates fabrics lower tensile strength

Acid Rain 1. Unpolluted rain water is slightly acidic, with a pH about This is because rain water reacts with CO 2 in the air to form H 2 CO Rain water with pH values lower than 5.7 is called acid rain.

Formation of acid rain Acid rain is formed when air pollutants such as SO 2 and NO 2 dissolved in rain water. SO 2 + H 2 O H 2 SO 3 2NO 2 + H 2 O → HNO 3 + HNO 2

Harmful effects of acid rain Soil become too acidic for plants to grow. Forest are seriously damaged. River and lakes become more acidic. Some aquatic plants and animals may die. The corrosion of metal will be speeded up. Damages building materials e.g. limestone and marble. All these materials contain CaCO 3 which reacts with acid.

Controlling of acid rain Reducing pollution from motor vehicles and industries. Neutralizing the acid s in soil and water using lime. Burning less fossil fuels.

Methods of minimizing pollutants from the burning fuels A. Motor vehicles 1. Fitting catalyst converters to motor vehicles. 2. Using unleaded petrol. -- lead emission into the air can be greatly reduced. 3. Using LPG instead of diesel. -- it is much cleaner fuel than diesel. 4. Using alcohol instead of petrol. -- it is much cleaner fuel than petrol.

Catalytic Converter – Fitting a catalytic converter to the exhaust pipes of motor vehicles. – A catalytic converter is a stainless steel cylinder containing a honeycomb structure coated with platinum as catalyst. –Since the catalyst is easily poisoned by lead, it can only work efficiently on unleaded petrol.

Catalytic Converter In the first half of the catalytic converter, poisonous gases, CO and NO react catalytically to form harmless CO2 and N2. 2CO (g) + 2NO (g)  2CO 2(g) + N 2(g) In the second half of the converter, hydrocarbons and any remaining CO are oxidized to CO2 and H2O. 2CO (g) + O 2(g)  2CO 2(g) C x H y(l) + (x + y/4) O 2(g)  xCO 2(g) + y/2 H 2 O (l)

B. Factories 1. Using cleaner fuels with low sulphur content e.g. diesel fuel 2. Using scrubber -- Acidic sulphur oxide can be removed by reacting with alkalis to form sulphites or sulphates. 3. Using electrostatic precipitators -- Unburned small solid particles can be removed by this method.

Scrubber A) Dry Scrubber Powdered limestone is added to the hot gases from burning coal. The heat decomposes the limestone to give lime. CaCO3(s)  CaO(s) + CO2(g) The lime then react with sulphur dioxide to give calcium sulphite. CaO(s) + SO2(g)  CaSO3(g) The calcium sulphite reacts with air to give calcium sulphate. 2CaSO3(s) + O2(g)  2CaSO4(g)

Electrostatic Precipitators The solid particles in the smoke becomes negatively charged when passing through a high voltage electric field. The negatively charged particles then attracted to the positive electrodes and stick to the sides of the precipitator. The particles are then shaken to the bottom by the continuous knocking of a steel hammer. Electrostatic Precipitator are usually used in incinerators and power stations.