Question

Difficulty: HardAir Pollutants, Photochemical Smog, and Acid Rain

Automotive exhaust emissions significantly contribute to atmospheric pollution. Which of the following chemical reactions occurring inside a catalytic converter directly eliminates a primary pollutant that acts as a precursor to both photochemical smog and acid rain?

  1. The reduction of nitrogen(II) oxide (NONO) to nitrogen gas (N2N_2)Answer
  2. B
    The oxidation of carbon(II) oxide (COCO) to carbon(IV) oxide (CO2CO_2)
  3. C
    The catalytic breakdown of chlorofluorocarbons (CFCsCFCs) into halide salts
  4. D
    The desulfurization of sulfur(IV) oxide (SO2SO_2) by reaction with calcium oxide (CaOCaO)

Answer

The reduction of nitrogen(II) oxide (NONO) to nitrogen gas (N2N_2)
Nitrogen(II) oxide (NONO) produced in internal combustion engines is a primary pollutant. Inside a catalytic converter, reduction catalysts convert NONO into harmless nitrogen gas (N2N_2). This prevents NONO from oxidizing in the atmosphere to NO2NO_2, which is essential for driving the photochemical reactions that produce tropospheric ozone and PAN (photochemical smog) as well as nitric acid (HNO3HNO_3) in acid rain.

Step-by-Step Solution

1
Identify the primary pollutant responsible for both photochemical smog and acid rain
Nitrogen oxides (NOxNO_x, primarily NONO and NO2NO_2) are key precursors for both atmospheric issues.
NO2NO_2 reacts with sunlight and volatile organic compounds to generate tropospheric ozone (photochemical smog) and dissolves in moisture to form nitric acid (HNO3HNO_3).
2
Determine the role of the catalytic converter in treating nitrogen oxides
The reduction catalyst (platinum and rhodium) converts NONO into harmless N2N_2 gas: 2NON2+O22NO \rightarrow N_2 + O_2.
By reducing NONO before exhaust release, the formation of secondary atmospheric pollutants is prevented.

Key Concept

Role of catalytic converters in reducing NOxNO_x precursors of photochemical smog and acid rain
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