Describe the role of oxides of nitrogen in the formation of photochemical smog and their removal by catalytic converters, e.g. $2 mathrm{CO}+2 mathrm{NO} ightarrow 2 mathrm{CO}_2+mathrm{N}_2$

Chemistry of the Environment – Air Quality & Climate

1. What are oxides of nitrogen (NOx)?

NOx includes NO and NO₂, produced mainly by combustion engines and power plants. They are like the “bad breath” of the atmosphere, causing smog and acid rain. 😷

2. How do NOx create photochemical smog?

When sunlight hits NOx, a chain of reactions starts, turning harmless NO₂ into powerful oxidisers that attack VOCs (volatile organic compounds). Think of it as a chemical domino effect. 🧩

  • NO₂ + sunlight → NO + O (atomic oxygen)

  • O + O₂ → O₃ (ozone)

  • O₃ + VOCs → peroxy radicals → more NO₂

3. Key reaction: Catalytic converter in cars

A catalytic converter uses a platinum‑tungsten catalyst to turn harmful gases into harmless ones. The reaction you mentioned:

\$2\,\mathrm{CO} + 2\,\mathrm{NO} \;\longrightarrow\; 2\,\mathrm{CO}2 + \mathrm{N}2\$

Here, carbon monoxide (CO) and nitrogen oxides (NO) are “cooked” into carbon dioxide and nitrogen gas.

4. Step‑by‑step catalytic conversion

  1. CO + O₂ → CO₂ (oxidation)

  2. NO + NO₂ → N₂O₄ (dimerisation)

  3. Overall: 2CO + 2NO → 2CO₂ + N₂

5. Exam tips 📚

  • Remember the role of sunlight: It breaks NO₂ into NO + O.

  • Key products: O₃ (ozone), CO₂, N₂.

  • Write balanced equations: Always check atoms on both sides.

  • Use analogies: Compare NOx to “bad breath” that turns into “clean air” in the converter.

6. Quick quiz

  1. What is the main source of NOx in urban areas? (Answer: Combustion engines)

  2. Which gas is produced when NO₂ is exposed to sunlight? (Answer: O + NO)

  3. In the catalytic converter, which element is the catalyst? (Answer: Platinum/Tungsten)