1.2 Photochemical Smog

• Combustion of fossil fuels produces primary pollutants like CO2, soot, CO, NO and SO2.

  Note that SO2 comes from contamination of crude oil...
• The primary pollutants react with the air and use UV to make secondary pollutants like NO2, O3, PANs and H2SO4 & HNO3

  N2+O2 -temp-> 2NO

  2NO + O2 -> 2NO2

  NO2 is a brown gas that contributes to urban haze, lowering visibility
• NO2 can absorb sunlight and photodissociate to make O3

  NO2 ---UV--> NO + O,

  O + O2 --> O3 in troposphere,

  Ozone can cause bad respiratory issues because it likes to oxidize everything .
• Photochemical smog is a mixture of primary and secondary pollutants, which tropospheric ozone and NO2 are the main ones. This can damage respiratory tissues through inhalation, and can cause eye irritation. Ozone is highly reactive and can prevent plants from photosynthesis, damaging fabrics and rubber materials
• Thermal inversions can occur due to a lack of air movement when a layer of dense, cool air is trapped beneath a layer of less dense, warm air.

  Hence, the concentrations of air pollutants build up instead of being dissipated by wind.
• Catalytic converters can use reduction reaction

  2NO -> N2 + O2

  and

  CO + NOx -> CO2 + N2
• Catalytic converters can also use oxidation reaction

  2CO + O2 -> 2CO2

  C5H12 [any hydrocarbon] + 8O2 -> 5CO2 + 6H2O
• The metal catalyst from the catalytic converter provides an alternate reaction pathway with a lower activation energy. This provides a greater proportion of collisions between reactant particles, increasing the rate of reaction, and can be reused over and over. Its honeycomb structure also increases rate of reaction.
• pollutants are Substance released into environment which has harmful effect