ALTERNATIVE FUEL MOTOR-VEHICLE TAILPIPE AND EVAPORATIVE EMISSIONS COMPOSITION AND OZONE POTENTIAL

The 1988 Alternative Motor Fuels Act and the 1990 Clean Air Act Amendm ents require examination of the potential to favorably influence air q uality by changing the composition of motor vehicle fuels. Motor vehic le tailpipe and evaporative emissions were characterized using laborat ory simulations of roadway driving conditions and a variety of vehicle -fuel technologies (reformulated gasoline (RFG), methanol (M85), ethan ol (E85), and natural gas (CNG)). Speciated organic compound (with Car ter MIR ozone potential), CO, and NOx emission rates and fuel economy were characterized. The Carter MIR clone potential of combined Federal Test Procedure (FTP) tailpipe and evaporative emissions was reduced m ore than 90% with CNG relative to RFG, M85, and E85 fuels. FTP toxic c ompound emissions (benzene, formaldehyde, acetaldehyde, and 1,3-butadi ene) were greater with M85 and E85 fuels than with RFG fuel, and less with CNG fuel than RFG fuel. The most abundant toxic compound was benz ene with RFG fuel, formaldehyde with M85 fuel, and acetaldehyde with E 85 fuel. FTP MPG fuel economies were reduced with M85 and E85 fuels re lative to RFG fuel, consistent with their lower BTU/gal. Energy effici encies (BTU/mi) were improved with all the alternative fuels relative to RFG. Carter MIR ozone potential was generally reduced with the alte rnative fuels relative to RFG fuel under REP05 (high speeds and accele ration rates) driving conditions (most significantly with CNG). Toxic aldehyde emissions were reduced under REP05 conditions relative to FTP conditions with all the tested fuels, and toxic benzene emissions wer e elevated under high acceleration conditions.