Urban vegetation is associated with numerous public health benefits; however, urban tree canopies may be threatened by fugitive methane exposure from leaky natural gas distribution systems. Despite anecdotal evidence of the harmful impacts of natural gas leaks on urban tree decline, the relationship between soil gas exposure and tree health has not been formally quantified in an urban setting. We conducted a case-control study to compare soil natural gas exposure in sidewalk tree pits of healthy and dead or dying trees in Chelsea, Massachusetts, during summer 2019. We measured soil concentrations of methane and oxygen at four points around the trunks of 84 case and 97 control trees. We determined that case trees had 30 times the odds of being exposed to detectable levels of soil methane relative to the control trees sampled (95% CI = 3.93, 229). Among tree pits with elevated soil gas, we also found that methane concentrations were highest on the side of the tree pit closest to the street. These results contribute evidence to support the widespread belief that soil methane exposure can negatively impact urban tree health. They also suggest that fugitive methane leakage from urban natural gas distribution systems beneath the street surface may be responsible for elevated soil gas concentrations in sidewalk tree pits and subsequent tree death.

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天然气泄漏和树木死亡：美国马萨诸塞州切尔西市城市树木的初步病例对照研究。

城市植被与许多公共健康益处相关；然而，城市树冠可能会受到天然气分配系统泄漏的逸散甲烷的威胁。尽管有传闻证据表明天然气泄漏对城市树木衰退造成有害影响，但城市环境中土壤气体暴露与树木健康之间的关系尚未得到正式量化。我们进行了一项病例对照研究，以比较 2019 年夏季马萨诸塞州切尔西市人行道树坑中健康、死亡或​​垂死树木的土壤天然气暴露情况。我们测量了 84 个案例树干周围四个点的土壤甲烷和氧气浓度和97个控制树。我们确定，相对于采样的对照树木，案例树木暴露于可检测到的土壤甲烷水平的几率是对照树木的 30 倍 (95% CI = 3.93, 229)。在土壤气体升高的树坑中，我们还发现离街道最近的树坑一侧甲烷浓度最高。这些结果提供了证据支持人们普遍认为土壤甲烷暴露会对城市树木健康产生负面影响。他们还认为，街道表面下方的城市天然气分配系统的逸散性甲烷泄漏可能是导致人行道树坑土壤气体浓度升高以及随后树木死亡的原因。