Mitigation of methane emissions in cities: How new measurements and partnerships can contribute to emissions reduction strategies

Abstract

Cities generate 70% of anthropogenic greenhouse gas emissions, a fraction that is growing with global urbanization. While cities play an important role in climate change mitigation, there has been little focus on reducing urban methane (CH 4 ) emissions. Here, we develop a conceptual framework for CH 4 mitigation in cities by describing emission processes, the role of measurements, and a need for new institutional partnerships. Urban CH 4 emissions are likely to grow with expanding use of natural gas and organic waste disposal systems in growing population centers; however, we currently lack the ability to quantify this increase. We also lack systematic knowledge of the relative contribution of these distinct source sectors on emissions. We present new observations from four North American cities to demonstrate that CH 4 emissions vary in magnitude and sector from city to city and hence require different mitigation strategies. Detections of fugitive emissions from these systems suggest that current mitigation approaches are absent or ineffective. These findings illustrate that tackling urban CH 4 emissions will require research efforts to identify mitigation targets, develop and implement new mitigation strategies, and monitor atmospheric CH 4 levels to ensure the success of mitigation efforts. This research will require a variety of techniques to achieve these objectives and should be deployed in cities globally. We suggest that metropolitan scale partnerships may effectively coordinate systematic measurements and actions focused on emission reduction goals.

Methane Mitigation: Methods to Reduce Emissions, on the Path to the Paris Agreement

“…Such loss rates are expensive, locally potentially dangerous, and an unnecessary greenhouse emission. Yet currently many jurisdictions pay little attention to mitigating urban gas leaks: for example, in the United States, Hopkins et al () concluded that “current mitigation approaches are absent or ineffective.” Even safety can be neglected. A recent example is the series of explosions and fires in the Merrimack valley, Massachusetts, USA, in September 2018 that killed one person and damaged over a hundred buildings (NTSB, ).…”

“…Such loss rates are expensive, locally potentially dangerous, and an unnecessary greenhouse emission. Yet currently many jurisdictions pay little attention to mitigating urban gas leaks: for example, in the United States, Hopkins et al (2016) concluded that "current mitigation approaches are absent or ineffective." Even safety can be neglected.…”

Consumption‐Based Accounting of Global Anthropogenic CH4 Emissions

“…Production‐based emission accounting (PBA) represents the on‐site emissions within national territory (sometimes referred to as territorial‐based) preferred by the UNFCCC. Existing studies whether regarding national, regional, and sectoral CH 4 emissions are all in the scope of PBA circumstance (e.g., Du et al, ; Höglund‐Isaksson, ; Hopkins et al, ; Janssens‐Maenhout et al, ; B. Zhang, Chen, et al, ). But GHG emissions from various industrial sectors are induced by economic behaviors (Oliveira & Bourscheidt, ).…”

Vista-LA: Mapping methane-emitting infrastructure in the Los Angeles megacity

“…Many wastewater treatment plants also use anaerobic digesters which collect CH 4 for eventual combustion, but may have fugitive CH 4 emissions. Of the urban sources of CH 4 , this source is perhaps the most uncertain (Hopkins et al, 2016a). For the purposes of this study, we assume CH 4 emissions are most likely to arise from the plants with the largest daily flow capacity; however, emissions could also potentially arise from various points of collection and/or drainage of wastewater and sewage.…”

“…We chose the IPCC approach because it is more standardized, and hence applicable to other cities. The lifecycle approach requires local knowledge, and is likely to differ among cities and regions (Hopkins et al, 2016a). We also assumed that most CH 4 emissions come from the main facility associated with an emitting activity, such as wastewater treatment plants for wastewater emissions, rather than the sewer network.…”