ch17g

**Chapter 17 Section G: Photochemical Smog** http://unitedcats.files.wordpress.com/2007/07/ozone-pollution-smog.jpg - Smog = Sm oke + Fog - Photochemical smog is formed by the reactions of automobile exhaust in the presence of sunlight - Automobile exhaust consists of NO, CO, and various unburned hydrocarbons - These gases (primary pollutants) set in motion a series of photochemical reactions that produce - secondary pollutants NO2 and O3, causing smog

N2(g) + O2(g) → 2NO(g) Automobile engine 2NO(g) + O2(g) → 2NO2(g) Atmosphere NO2(g) + //hv// → NO(g) + O(g) Sunlight (//hv// = emitted photon) O(g) + O2(g) + M → O3(g) + M (M = some inert substance, i.e. N2)

- Ozone attacks the C=C linkage in rubber. It can cause car tires to crack in smog-ridden areas - The process that produces ozone also produces peroxyacetyl nitrate (PAN), a compound that causes - tearing and breathing difficulties - The oxidation of hydrocarbons produces organic intermediates such as alcohols and carboxylic acids - which eventually condense into small droplets of liquid known as aerosol, making the air hazy

- Recently efforts have been made to curb harmful automobile exhaust - Many cars not have catalytic converters that oxidize CO and hydrocarbons to CO2 and H2O - A new technology coats automobile radiators and air conditioner compressors with a platinum - catalyst, purifying the air that flows under the hood - Using this technology, driving would actually improve the quality of the air!

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