The boxes and whiskers for our observations show 5th, 25th, 50th, 75th, and 95th percentiles of the observed EFs. Black dots and bars show the average values and standard errors of corresponding EFs measured in China. Black dots and bars show the average values and standard deviation (S.D.) of corresponding EFs measured in China. Numbers of independent samples (vehicles) used to derive EFs and the standard errors are listed in the labels. Red dots and bars show the venting-emission and seasonality adjusted values of corresponding EFs for China. Gray dots and bars show the average values and standard errors of corresponding EFs measured in other regions. The star and the associated bar show the estimated EF and its uncertainty for heavy-duty NG trucks equipped with a lean-burn engine and oxidation catalyst (determination of the uncertainty can be found in method section). Xie et al. and Guo et al. measured total hydrocarbon (THC) emissions instead of CH423,52. We converted their results to CH4 emissions assuming 90% of THC is CH4 as suggested by Xie et al. and Hu et al.23,52. The observed EF for heavy-duty vehicles is 85% higher than the current standard (China V). “LB + OC”, “SM + TWC”, “SM + TWC w. CC”, “HPDI”, and “HPDI w. DV” stand for a lean-burn engine with oxidation catalyst, stoichiometric engine with three-way catalyst, stoichiometric engine with a three-way catalyst with crankcase emissions, high-pressure direct injection (HPDI), and HPDI with dynamic venting emissions. Source data are provided as a Source Data file.