What gases are typically reduced with the use of an air pump during emissions testing?

The choice of hydrocarbons (HC) and carbon monoxide (CO) is pertinent because these are two significant pollutants that vehicles emit, particularly in older models or those with malfunctioning systems. The introduction of an air pump during emissions testing serves to oxidize hydrocarbons and carbon monoxide, thereby converting them into less harmful substances through combustion. This process helps to lower the concentration of these gases in exhaust emissions, which is crucial for meeting environmental regulations and promoting air quality.

Hydrocarbons are a product of incomplete combustion of fuel, and their presence in vehicle emissions contributes to smog and other air quality concerns. Carbon monoxide, a poisonous gas produced when carbon in fuel does not fully combust, also poses health risks. By enhancing the combustion process, an air pump effectively reduces the levels of these harmful emissions in a controlled testing environment.

In contrast, the other gases listed in the options have different relevance or are typically not the primary targets of an air pump during emissions testing. Nitrogen oxides (NOx) are regulated through other means, while sulfur dioxide (SO2) and particulate matter (PM) relate more to fuel composition and combustion efficiency rather than direct air injection. O2 and CO2 are necessary components of combustion, with CO2 being