The third of the three vital parts of the California Smog Check. This is where the emissions analyzer tests actual emissions from your vehicle, as measured at the tailpipe. Only the emissions test can label a car a Gross Polluter. Emissions measured include Carbon Monoxide (CO), Carbon Dioxide (CO2), Hydrocarbons (HC) and Oxygen (O2). In California’s most polluted urban areas (Enhanced Areas), the emissions test also measures levels of oxides of nitrogen (NOx).