Emission Gases Explained Pt.1

Pt.2 / Pt.3 / Pt.4 / Pt.5

General Background 

Concentration of combustion products in the vehicle's exhaust, most of which pollute the air, give important diagnostic clues to the vehicle's engine efficiency. The component gases which contribute the most to air pollution are hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx). Three of the five gases measured at the tailpipe are regulated pollutants - HC, CO and NOx. The remaining gases, oxygen (O₂) And carbon dioxide (CO₂), while non-regulated, play a significant role as diagnostic aids. A four gas analyzer measures HC, CO, CO₂ and O₂ concentrations. The five gas analyzer adds the measurement of NOx as well.

An exhaust gas analyzer is a highly versatile and accurate test instrument. In addition to testing carbon monoxide (CO), carbon dioxide (CO₂), oxygen (O₂), hydrocarbons (HC) and oxides of nitrogen (NOx) (for the 5-gas version) for repair requirements or after a tune-up, it can be used to assist in detecting and locating, fuel, exhaust, emission control and engine service problems.