Difficulty: Easy
Correct Answer: CO
Explanation:
Introduction / Context: Road vehicles emit a mixture of pollutants. Historically, before widespread catalytic converters and stringent standards, one compound dominated public-health concerns from gasoline engines: carbon monoxide (CO).
Given Data / Assumptions:
Concept / Approach: CO forms from incomplete combustion of carbon in fuel. In spark-ignition engines, CO fractions in raw exhaust are relatively high compared with many other toxic components. CO is colorless, odorless, and interferes with oxygen transport in blood, making it a critical pollutant historically targeted by automotive catalysts.
Step-by-Step Solution:
Compare pollutants: CO vs CO2 vs NO vs hydrocarbons.CO2 is a greenhouse gas but not a toxic “pollutant” in the same acute sense at tailpipe levels.NO is a component of NOx, significant but typically controlled with three-way catalysts; raw SI exhaust still has more CO by mass.Unburned hydrocarbons are important for smog but often lower than CO in raw SI exhaust streams.Verification / Alternative check: Emission inventories and textbook data show high CO percentages in untreated gasoline engine exhaust, validating CO as the principal pollutant historically addressed.
Why Other Options Are Wrong:
CO2: A climate pollutant, but not the principal toxic exhaust pollutant targeted by local air-quality standards.NO: Part of NOx; important but usually less dominant than CO in untreated SI exhaust.Hydrocarbons: Contribute to ozone and photochemical smog, yet CO typically predominates by mass in raw gasoline exhaust.Common Pitfalls: Confusing climate relevance (CO2) with acute toxicity (CO), and conflating diesel vs gasoline emission profiles.
Final Answer: CO
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