Photochemical Smog
Catalytic converter - ANS - It is possible to reduce the quantities of nitrogen oxide
generated by cars
- A catalytic converter has a very thin layer of platinum group metals (Pt, Pd, Ni, Rh, Ir)
coated on a honeycomb structure
- As exhaust gases come into contact with the catalyst, a number of chemical reactions
occur on the catalyst surface (a honeycomb to increase surface area)
- The catalyst surface of a catalytic converter needs to be at an optimum temperature,
and so during short journeys the catalytic converter will not work
- At the surface, using catalysts, the following reactions will occur:
- Oxidation of CO to form CO₂
2CO(g) + O₂(g) → 2CO₂(g) (requires light)
- Combustion of unburnt hydrocarbons to
CO₂ + H₂O
e.g. 2C₈H₁₈ + 2SO₂ → 16CO₂ +18H₂O (needs
catalyst)
- NO reduced to N₂
2CO + NO → N₂ + CO₂ (needs catalyst)
- Catalytic converters have reduced photochemical smog but they do increase the
production of CO
\Environmental concerns of photochemical smog - ANS - Ozone (O₃) is highly corrosive
and attacks mucous membranes of the respiratory tract and eyes, it will attack rubber
and wood, and it damages the surface of leaves resulting in significant decreases in the
rate of photosynthesis
\Formation of nitrogen oxides - ANS - Nitrogen oxides are formed in high temperature
engines and furnaces
- Nitric oxide, NO, is formed by the reaction between atmospheric nitrogen and oxygen at
high temperatures in cars and industrial furnaces
N₂(g) + O₂(g) → 2NO(g) (high energy required) (colourless)
- Once released into the atmosphere, the nitric acid is rapidly converted to nitrogen
dioxide. Nitrogen dioxide is classified as a primary pollutant
2NO(g) + O₂(g) → 2NO₂(g) (brown)
\Formation of ozone in the troposphere - ANS - The troposphere is the closest layer to
the surface of the earth
N₂ + O₂ → 2NO (primary pollutant)
NO + O₂ → 2NO₂ (secondary pollutant)
NO₂ ⇌ NO + O° (high energy free radical, has absorbed energy) (requires sunlight)
O₂ + O° + M → O₃ + M° (M absorbs the energy of the O free radical)
M=stabilising molecule (N₂)
- The concentration of NO will gradually increase as more cars are on the road
- This NO will react further to form NO₂
Catalytic converter - ANS - It is possible to reduce the quantities of nitrogen oxide
generated by cars
- A catalytic converter has a very thin layer of platinum group metals (Pt, Pd, Ni, Rh, Ir)
coated on a honeycomb structure
- As exhaust gases come into contact with the catalyst, a number of chemical reactions
occur on the catalyst surface (a honeycomb to increase surface area)
- The catalyst surface of a catalytic converter needs to be at an optimum temperature,
and so during short journeys the catalytic converter will not work
- At the surface, using catalysts, the following reactions will occur:
- Oxidation of CO to form CO₂
2CO(g) + O₂(g) → 2CO₂(g) (requires light)
- Combustion of unburnt hydrocarbons to
CO₂ + H₂O
e.g. 2C₈H₁₈ + 2SO₂ → 16CO₂ +18H₂O (needs
catalyst)
- NO reduced to N₂
2CO + NO → N₂ + CO₂ (needs catalyst)
- Catalytic converters have reduced photochemical smog but they do increase the
production of CO
\Environmental concerns of photochemical smog - ANS - Ozone (O₃) is highly corrosive
and attacks mucous membranes of the respiratory tract and eyes, it will attack rubber
and wood, and it damages the surface of leaves resulting in significant decreases in the
rate of photosynthesis
\Formation of nitrogen oxides - ANS - Nitrogen oxides are formed in high temperature
engines and furnaces
- Nitric oxide, NO, is formed by the reaction between atmospheric nitrogen and oxygen at
high temperatures in cars and industrial furnaces
N₂(g) + O₂(g) → 2NO(g) (high energy required) (colourless)
- Once released into the atmosphere, the nitric acid is rapidly converted to nitrogen
dioxide. Nitrogen dioxide is classified as a primary pollutant
2NO(g) + O₂(g) → 2NO₂(g) (brown)
\Formation of ozone in the troposphere - ANS - The troposphere is the closest layer to
the surface of the earth
N₂ + O₂ → 2NO (primary pollutant)
NO + O₂ → 2NO₂ (secondary pollutant)
NO₂ ⇌ NO + O° (high energy free radical, has absorbed energy) (requires sunlight)
O₂ + O° + M → O₃ + M° (M absorbs the energy of the O free radical)
M=stabilising molecule (N₂)
- The concentration of NO will gradually increase as more cars are on the road
- This NO will react further to form NO₂
