Which of the following gases is released into the air by automobile exhaust? 

The correct answer is CO.

Key Points

• Carbon monoxide (CO) is a major pollutant released from automobile exhaust due to the incomplete combustion of fuel.
• CO is a colorless, odorless, and toxic gas that binds with hemoglobin in the blood, reducing the oxygen-carrying capacity of red blood cells.
• Automobiles that run on petrol and diesel are the primary sources of CO emissions in urban areas.
• Strict emission standards like Bharat Stage (BS) norms in India aim to reduce CO emissions from vehicles.
• Use of catalytic converters in vehicles significantly reduces CO emissions by converting it into less harmful gases like CO₂.

Additional Information

• Incomplete Combustion:
  • Occurs when there is insufficient oxygen to completely oxidize the fuel, producing carbon monoxide (CO) instead of carbon dioxide (CO₂).
  • Incomplete combustion is common in poorly maintained or older vehicles.
• Impact of CO on Health:
  • CO binds to hemoglobin with an affinity 200–250 times greater than oxygen, leading to a condition known as carboxyhemoglobinemia.
  • Symptoms of CO exposure include headaches, dizziness, confusion, and in severe cases, it can be fatal.
• Emission Control Technologies:
  • Catalytic converters reduce CO emissions by facilitating the oxidation of CO into CO₂.
  • Adoption of electric and hybrid vehicles reduces dependence on internal combustion engines, thereby lowering CO emissions.
• Regulatory Standards:
  • Countries adopt stringent vehicular emission norms such as Euro standards in Europe and Bharat Stage (BS) norms in India to limit CO and other pollutant levels.
  • BS-VI standards in India mandate a significant reduction in CO emissions compared to earlier norms.