Humphrey School of Public Affairs, University of Minnesota, Minneapolis 55455, Minnesota, United States.
Department of Civil and Environmental Engineering, Princeton University, Princeton 08544, New Jersey, United States.
Environ Sci Technol. 2020 Dec 15;54(24):16086-16096. doi: 10.1021/acs.est.0c02723. Epub 2020 Nov 20.
Biogenic CO emissions in cities are shaped by urban land cover change which can release carbon stocks, and, carbon sequestration by in situ vegetation. To date, these two processes have not been studied together and compared with transboundary fossil fuel-based CO emissions of urban energy use. We leverage remote sensing and machine learning to quantify biogenic CO emissions between 2006 and 2012, across 11 U.S cities, including central and suburban cities, in different climate zones. Results indicate that in situ carbon sequestration by greenery varied moderately across cities (-2.1 to -0.87 Mg CO ha yr), while emissions from the carbon stock change due to land conversion varied much more (-3.4 to 9.8 Mg CO ha yr), indicating that the latter dominates biogenic CO emissions. Net biogenic CO emissions were negative (carbon sink) in four cities, while large net positive emissions were present in rapidly growing suburbs. As a ratio of community-wide energy use for travel and buildings, biogenic CO emissions were a small proportion in the core cities Denver (0.17%) and Minneapolis (0.33%) and as high as 38.2% in growing exurban communities. These results show that land cover change and greenery will be important policy levers in zero-carbon city planning.
城市的生物成因 CO 排放受城市土地覆被变化的影响，土地覆被变化会释放碳储量，并促进原地植被的碳固存。迄今为止，这两个过程尚未一起进行研究，也未与城市能源利用的跨境化石燃料基 CO 排放进行比较。我们利用遥感和机器学习技术，量化了 2006 年至 2012 年期间美国 11 个城市（包括不同气候带的中心城市和郊区城市）的生物成因 CO 排放。结果表明，绿化的原地碳固存情况在各城市之间差异不大（-2.1 至-0.87 Mg CO ha yr），而土地转换导致的碳储量变化引起的排放则差异较大（-3.4 至 9.8 Mg CO ha yr），这表明后者主导了生物成因 CO 排放。四个城市的净生物成因 CO 排放为负值（碳汇），而在快速发展的郊区则存在较大的净正排放。就旅行和建筑用社区范围内能源使用而言，生物成因 CO 排放量在丹佛（0.17%）和明尼阿波利斯（0.33%）等核心城市中占比较小，而在不断发展的远郊社区中则高达 38.2%。这些结果表明，土地覆被变化和绿化将成为零碳城市规划中的重要政策手段。
