Characterizing start emissions of gasoline vehicles and the seasonal, diurnal and spatial variabilities in China

Start emissions from gasoline light-duty passenger vehicles (LDPVs) remain an important source of emissions modeling. This study measured start emissions of gaseous pollutants and solid particle number based on dynamometer tests for a fleet of 111 LDPVs in China, and selected a portion of samples to be tested under low temperature or shorter soak conditions. The cold-start phase, defined to follow soak durations of more than 6 h, typically lasts less than 200 s but accounts for a high proportion of total tailpipe emissions under the regulatory cycle (e.g., similar to 60% for China 6 CO emissions). Low temperature predominantly increases start emissions rather than hot-running emissions, and the increase ratios vary by pollutant and vehicle technology. Metrological data and soak duration profiles informed by a large sample of LDPVs were used to quantify the seasonal, diurnal and spatial variabilities of LDPV emissions across China. One notable case indicates that tailpipe THC emissions in January could be 283% higher than those in July for the fleet in Beijing, and the emissions peak in the morning rush hour during a day due to long overnight soak durations. This study provides a comprehensive dataset and useful tools for addressing the seasonal, diurnal and spatial variations in tailpipe emissions of gasoline vehicles in China, and has the potential to improve future emission inventories and air quality simulations.