Impact of Cold Climates on Vehicle Emissions: The Cold Start Air Toxics Pulse

Tom Jobson et al.
Wed, 22 Apr 2026 17:15:14 PDT

This project measured cold start emissions from four vehicles in winter using fast response instrumentation to accurately measure the time variation of the cold start emission pulse. Seventeen successful tests were conducted over a temperature range of -4°C to 10°C in winter 2015 at the Washington State University campus. Vehicle cold starts are thought to be a significant source of air toxic compounds in cold winter environments due to the rapid increase in mass emission rates with decreasing temperature. We used a proton transfer reaction mass spectrometer for high time resolution measurement of the emissions the air toxic compounds benzene, formaldehyde, acetaldehyde, in addition to toluene and C2-alkylbenzenes. Measured molar emission ratios relative to toluene in the cold start pulse were compared with cold start emission profiles for E10 fueled vehicles used in the EPA MOVES2014 model. We found that the measured acetaldehyde-to-toluene emission ratio was about a factor of 8 greater than the emission ratio used in MOVES2014. Measured formaldehyde-to-toluene emission ratios were a factor of 5 greater. Our study suggests that emission of the air toxics acetaldehyde and, likely, formaldehyde is significantly underestimated in wintertime by the MOVES2014 model.