NO2's Role in Smog Formation

Steps:

• Identify NO2 as a key pollutant from engines, formed via N2 + O2 → 2NO, then NO + 1/2 O2 → NO2.
• Recall NO2's photochemical role in oxidizing SO2 to sulfuric acid, contributing to acid rain and smog.
• Evaluate choices: A matches atmospheric catalysis; B confuses converter reactions; C/D misstate formation conditions.
• Confirm A via environmental chemistry: NO2 photolyzes to initiate SO2 oxidation.

Why A is correct:

• NO2 catalyzes SO2 oxidation in the troposphere via photolysis (NO2 → NO + O), where O reacts with O2 to form O3, and O3 oxidizes SO2 to SO3 (then H2SO4), per atmospheric chemistry laws.

Why the others are wrong:

• B: Catalytic converters reduce NO2 to N2 and O2, not form NO.
• C: NO2 forms from incomplete combustion at high temperatures, not pressure, and fuel impurities are minor.
• D: NO2 arises from high-temperature N2/O2 reactions in air, not fuel impurities or high pressure alone.

Final answer: A