Chapter 17 Section G: Photochemical Smog

- Smog = Smoke + 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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