John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138;
John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138.
Proc Natl Acad Sci U S A. 2021 Nov 2;118(44). doi: 10.1073/pnas.2105804118.
Across many cities, estimates of methane emissions from natural gas (NG) distribution and end use based on atmospheric measurements have generally been more than double bottom-up estimates. We present a top-down study of NG methane emissions from the Boston urban region spanning 8 y (2012 to 2020) to assess total emissions, their seasonality, and trends. We used methane and ethane observations from five sites in and around Boston, combined with a high-resolution transport model, to calculate methane emissions of 76 ± 18 Gg/yr, with 49 ± 9 Gg/yr attributed to NG losses. We found no significant trend in the NG loss rate over 8 y, despite efforts from the city and state to increase the rate of repairing NG pipeline leaks. We estimate that 2.5 ± 0.5% of the gas entering the urban region is lost, approximately three times higher than bottom-up estimates. We saw a strong correlation between top-down NG emissions and NG consumed on a seasonal basis. This suggests that consumption-driven losses, such as in transmission or end-use, may be a large component of emissions that is missing from inventories, and require future policy action. We also compared top-down NG emission estimates from six US cities, all of which indicate significant missing sources in bottom-up inventories. Across these cities, we estimate NG losses from distribution and end use amount to 20 to 36% of all losses from the US NG supply chain, with a total loss rate of 3.3 to 4.7% of NG from well pad to urban consumer, notably larger than the current Environmental Protection Agency estimate of 1.4% [R. A. Alvarez , 361, 186-188 (2018)].
在许多城市，基于大气测量的天然气（NG）分配和终端使用的甲烷排放量估算值通常比自上而下的估算值高出一倍以上。我们进行了一项针对波士顿市区 NG 甲烷排放的自上而下的研究，时间跨度为 8 年（2012 年至 2020 年），以评估总排放量、季节性和趋势。我们利用波士顿及其周边五个地点的甲烷和乙烷观测数据，结合高分辨率传输模型，计算出 NG 甲烷排放量为 76 ± 18 Gg/yr，其中 49 ± 9 Gg/yr 归因于 NG 损耗。尽管城市和州都在努力提高 NG 管道泄漏的修复率，但在 8 年内，我们没有发现 NG 损耗率有显著变化。我们估计，进入市区的天然气中有 2.5 ± 0.5% 会损耗，这大约是自下而上估算值的三倍。我们发现自上而下的 NG 排放量与季节性 NG 消耗量之间存在很强的相关性。这表明，传输或终端使用等消耗驱动的损耗可能是清单中缺失的排放的一个重要组成部分，需要未来的政策行动。我们还比较了来自六个美国城市的自上而下的 NG 排放估算值，这些城市都表明，自下而上的清单中存在大量缺失的排放源。在这些城市中，我们估计 NG 在分配和终端使用中的损耗量占美国 NG 供应链所有损耗量的 20%至 36%，损耗率为从井场到城市消费者的 NG 的 3.3%至 4.7%，明显高于美国环保署目前估计的 1.4%[R. A. Alvarez，361，186-188（2018）]。
