Particle number emissions from fully warmed gasoline vehicles at various ambient temperatures

Road vehicles have become the primary source of fine particles in many large cities. Vehicle hot-start PN emissions at various ambient temperatures were studied previously. Still, these studies used the same rolling resistance setting at different ambient temperatures and the tests at various ambient temperatures have similar PN emissions. Vehicles get larger resistance at cold ambient temperatures, so this experimental setting (same resistance at various ambient temperatures) is beyond the natural conditions. To evaluate how ambient temperatures affect the PN emissions from fully warmed vehicles, two vehicles were tested at four ambient temperatures: −10 °C, 0 °C, 23 °C, and 40 °C. Vehicle resistance variations under different ambient temperatures were taken into consideration. The observed results proved that PN emission would significantly deteriorate under cold conditions even when the vehicles are thoroughly warmed. The PN emission factor at −10 °C could be six times higher than at 23 °C. The deteriorated PN emission is caused by enhanced fuel enrichment and GPF regeneration, and larger vehicle resistance under cold ambient temperatures is the underlying reason for the increased PN emission. For the first time, this study proved that PN emission from fully warmed vehicles would significantly deteriorate when the ambient temperature decreases. The results could be used for emission models, inventory, and regulations.