What emissions does Secondary Air Injection (AIS) reduce?

• A. NOx emissions.
• B. Particulate matter emissions.
• C. HC and CO emissions after the combustion process.
• D. Ozone formation.

Answer: (C)

Secondary Air Injection works by pushing fresh air into the exhaust so there’s extra oxygen available to oxidize pollutants that weren’t fully burnt in the engine. This helps complete the combustion of unburned fuel and carbon monoxide in the exhaust, especially when the engine is cold and the catalytic converter isn’t yet up to temperature. Thus, the most direct and consistent reduction is hydrocarbons (unburned HC) and carbon monoxide (CO) in the exhaust after combustion. It doesn’t target NOx or particulates as its primary function, and ozone formation is a downstream consequence of various precursors, not the direct focus of AIS.