Investigating changes in urban methane using a multiplatform approach anthropogenic methane (CH4) emissions are primarily driven by agricultural, energy generation, and waste management activities

Bottom-up emissions estimates tend to carry high levels of uncertainty and the range of fugitive CH4 sources are difficult to detect effectively. CH4 is the second most important driver of anthropogenic warming, and the greenhouse gas has a high warming potential and short lifetime relative to carbon dioxide (CO2). Due to these characteristics, rapidly mitigating CH4 emissions can be an effective near-term solution to slow the rate of warming while working towards long-term decarbonization. Urban CH4 emissions tend to be driven by fugitive natural gas and landfills, and studies have shown that bottom-up inventories consistently underestimate these emissions. Innovative methods will be necessary to effectively identify natural gas leaks in dense urban systems. We propose to investigate emerging changes in urban CH4 emissions that are a consequence of current and growing mitigation strategies being broadly implemented through state and local regulations. We will characterize multi-year trends in SF BAY area urban CH4 by extending the operation of a currently 1-year funded stationary flux tower to at least 3-years of operation (operational in berkeley, CA as of april, 2022). We will use an intensive mobile monitoring campaign to evaluate the efficacy of this approach, identify fugitive sources, and better characterize major urban CH4 emissions source categories and specific facilities. We will work with community groups, building owners, and utility companies to mitigate any identified leaks within the flux tower observation range. We will utilize a mobile measurement platform which includes fast measurements for CH4, C2H6, 13CH4, CO2, N2O, CO, NOX, and vocs using a vocus-PTR instrument (aerodyne INC.). Measurement and analysis strategies will include: continued long-term fixed tower flux measurements by eddy covariance in berkeley, CA to characterize multi-year trends in urban CH4 emissions and evaluate the effectiveness of stationary flux towers for local fugitive source identification and quantification. The tower will include fast measurements for CH4, C2H6, CO2, N2O, CO, and NOX and VOC measurements to characterize seasonal variations in CH4 emission source categories. Intensive and systematic seasonal mobile source mapping within the domain of the flux tower to identify specific CH4 emission sources, characterize the diverse array of source chemical signatures, and improve the flux tower source attribution accuracy. In addition to a core program of spatial mapping, we will sample targeted sources (e.g., waste and composting facilities) to better constrain the impact of waste facilities. Integration of multiple lines of evidence from top-down (flux tower) and bottom-up (mobile mapping) approaches for constraining urban CH4 emissions at high spatiotemporal resolution. Assessment of key environmental justice dimensions of urban CH4 emissions, including quantification of disparities among neighborhoods in CH4 emissions density by race/ethnicity and historical redlining status, and the degree to which CH4 emissions are associated with hotspots of other air pollutants of local concern.