Anthropogenic CO₂ emissions from a megacity in the Yangtze River Delta of China

Anthropogenic CO₂ emissions from cities represent a major source contributing to the global atmospheric CO₂ burden. Here, we examined the enhancement of atmospheric CO₂ mixing ratios by anthropogenic emissions within the Yangtze River Delta (YRD), China, one of the world's most densely populated regions (population greater than 150 million). Tower measurements of CO₂ mixing ratios were conducted from March 2013 to August 2015 and were combined with numerical source footprint modeling to help constrain the anthropogenic CO₂ emissions. We simulated the CO₂ enhancements (i.e., fluctuations superimposed on background values) for winter season (December, January, and February). Overall, we observed mean diurnal variation of CO₂ enhancement of 23.5~49.7 μmol mol^-1, 21.4~52.4 μmol mol^-1, 28.1~55.4 μmol mol^-1, and 29.5~42.4 μmol mol^-1 in spring, summer, autumn, and winter, respectively. These enhancements were much larger than previously reported values for other countries. The diurnal CO₂ enhancements reported here showed strong similarity for all 3 years of the study. Results from source footprint modeling indicated that our tower observations adequately represent emissions from the broader YRD area. Here, the east of Anhui and the west of Jiangsu province contributed significantly more to the anthropogenic CO₂ enhancement compared to the other sectors of YRD. The average anthropogenic CO₂ emission in 2014 was 0.162 (± 0.005) mg m^-2 s^-1 and was 7 ± 3% higher than 2010 for the YRD. Overall, our emission estimates were significantly smaller (9.5%) than those estimated (0.179 mg m^-2 s^-1) from the EDGAR emission database.