emissions (automotive) - the three major pollutant emissions for which gasoline-powered vehicles are controlled are: unburned hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). Diesel-powered vehicles primarily emit NOx and particulates. Motor vehicles contribute only a small percentage of total man-made emissions of other atmospheric pollutants, such as sulfur oxides. Evaporative HC emissions from the fuel tank and carburetor are adsorbed by activated carbon contained in a canister installed on the vehicle. Blow-by HC emissions from the crankcase are controlled by positive crankcase ventilation (PCV). Exhaust emissions of HC, CO, and NOx - the products of incomplete combustion - are controlled primarily by a catalytic converter, in conjunction with exhaust gas recirculation and increasingly sophisticated technology for improving combustion efficiency, including electronic emission controls. See emissions (stationary source), hydro carbon emissions, pollutants.