Revealing Non-CO2 GHG Emissions in China's Transportation Networks

Despite the increasing role transportation plays in China's GHG emissions, CH4 and N2O emissions from mobile sources do not receive the attention they deserve. The CH4 and N2O emissions from each subsector of the transportation sector were analyzed from the bottom up in order to construct a detailed inventory of trends during 2010-2020. China's CH4 emissions from mobile sources increased from 440.6 (317.3-564.2) Gg [means range of uncertainty (minimum-maximum)] to 955.7 (635.8-1276.1) Gg. The N2O emissions increased steadily from 37.9 (24.7-58.9) Gg to 59.4 (33.3-88.1) Gg. Combining our own and other bottom-up inventories, we identify a significant underestimation of mobile-source CH4 emissions in China. Underestimating such emissions can largely be attributed to the significant increase in natural gas vehicles (NGVs) in China, which has taken place since 2010, and the uncertainty of NGVs' emission factors. Our results show that the mobile-source CH4 and N2O emissions in 2020 totalled 95.1 Mt CO2-eq (61.6-129.4) and 44.7 Mt CO2-eq (28.1-62.1) by the values of global warming potential at the 20-year and 100-year time period, almost as high as the CO2 emissions of Finland and New Zealand, respectively. To minimize the uncertainty of emission estimations, further field monitoring within transportation networks is urgently needed.