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SMOG

http://www.toronto.cbc.ca/features/smog/. SMOG. Application of Collision Theory. Smog “Smog” is a term that was coined about 100 years ago. Smog forms when smoke emissions are mixed with moist foggy air . The proper name is photochemical smog and it is produces a hazy, yellow-brown sky.

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SMOG

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  1. http://www.toronto.cbc.ca/features/smog/ SMOG Application of Collision Theory

  2. Smog • “Smog” is a term that was coined about 100 years ago. • Smog forms when smoke emissions are mixed with moist foggy air. • The proper name is photochemical smog and it is produces a hazy, yellow-brown sky.

  3. It is caused by the action of sunlight on nitrogen oxides (NOx) and hydrocarbon emissions from automobiles. • Smoggy air contains CO, NO, NO2, CxHy, and O3. • On smog alert days, breathing is uncomfortable, and the sky ‘looks ugly’.

  4. One of the most dangerous components of smog is ozone, O3. • Ground level ozone, O3, forms when the nitrogen monoxide from vehicle exhaust combines with O2 in the air.

  5. Smog Reaction Mechanism Step 1: NO + O2 → NO3 Step 2: NO3 + NO → 2 NO2 Step 3: 2 NO2 → 2 NO + 2 O Step 4: 2 O + 2 O2 → 2 O3 Identify all : 1) intermediates2) Catalysts

  6. Hooray for ozone production?? • in the upper atmosphere, ozone absorbs ultraviolet (uv) light and protects life on earth from the dangerous effects of uv light. • at ground level it irritates the respiratory tract and eyes, increases the risk of heart or lung disease, causes plant leaves to become brittle, bleaches colour from fabrics, and breaks down the elasticity of rubber. • Ozone is a nasty chemical at ground level! • The question becomes: how do we deal with it? • Based on the mechanism provided above, one way of preventing ozone formation at ground level is to get rid of the catalyst for the production of monoxygen.

  7. Ozone is a nasty chemical at ground level! Question: How do we deal with it? • Based on the mechanism provided above, one way of preventing ozone formation at ground level is to get rid of the catalyst for the production of monoxygen.

  8. The Catalytic Converter Modern catalytic converters have two purposes. • One is to convert carbon monoxide and nitrogen monoxide to nitrogen and carbon dioxide. • The other is to convert unburned hydrocarbons (which are responsible for PAN's - another component of smog) to carbon dioxide and water

  9. The Catalytic Converter

  10. The Catalytic Converter - There are different designs of catalytic converters on the market. - The catalysts may vary from one to another. - Common catalysts include: Pd, Pt, Rh, Ni2O3 ,Cu2O, & Cr2O3 - The internal honeycomb design maximizes the surface area available for contact between the exhaust gases from the engine and the metal or metal oxide catalysts

  11. Reaction Mechanism using catalyst Step 1: 2 CO(g) → 2 CO(ad) Step 2: NO(g) → N(g) + O(g) Step 3: N(g) + NO(g) → N2(g) + O Step 4: 2 CO(ad) + 2 O(g) → 2 CO2(g)

  12. Lead and Catalytic Converters Leaded gasoline molecules have four ethyl (CH3CH2-) groups bonded to a central lead atom. They burn evenly in car engines reducing a condition called engine ‘knock’ (which is associated with burning straight chain alkanes).

  13. Leaded gasoline banned by 1990 in Canada because: 1. of the poisonous effects of lead. • of its effect on the efficiency of catalytic converters. - Lead not only poisons people, it also "poisons" converters by binding to the catalysts. - Once it becomes covered in an impurity like lead, a converter can no longer adsorb CO and NO molecules.

  14. MTBE and Branched Hydrocarbons • The replacement for leaded gasoline molecules are highly branched hydrocarbons like 2,2,4-trimethylpentane. • However, the need for oxygen in gasoline has led to the use of an ether called methyl tert-butyl ether or MTBE.

  15. MTBE and Branched Hydrocarbons • It provides more oxygen to the combustion reaction and helps increase the amount of oxygen going into the converter to get rid of unburned hydrocarbons. • MTBE use is controversial. In gas tanks, it is not a problem, but is a problem in ground water and wells because it is a suspected carcinogen. It is finding its way into water supplies in cities and towns because of sloppy filling practices and gasoline spills.

  16. Handout: Smog, Catalytic converters and You. Textbook Readings MHR page 802: Automobile Engines (paragraph 1) Textbook Practice Items MHR page 487: item 19

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