Source category attribution of methane emissions in Calgary using Positive Matrix Factorization (PMF)

Cities emit methane (CH4) and have a role to play in mitigating the climate impacts of those emissions. Research suggests that CH4 emissions from most North American cities are dominated by sources associated with natural gas distribution and end use. In this work, we examine trace gas measurements from a central air monitoring station in Calgary, Alberta, Canada to attribute the city’s CH4 emissions to major source categories. Using Positive Matrix Factorization (PMF), we identified four primary CH4 emissions source categories: natural gas – fugitives, natural gas – incomplete combustion, waste/biogenic, and petroleum product processing. Results from PMF modeling indicate that the bulk of the CH4 emissions in Calgary are from natural gas fugitives and incomplete combustion (81% ± 35%). This is much higher than the proportion derived from available bottom-up emissions inventories. The CH4 emissions from natural gas sources increase in winter and may be related to increased natural gas use for space heating. Emissions from waste/biogenic sources were the next largest contributor, which doubled in warmer months, consistent with temperature-driven microbial activity. Though relatively small, CH4 emissions from petroleum product processing are non-negligible and consistent. Overall, these findings underscore the need for targeted mitigation strategies focused on the natural gas supply chain, while also highlighting the influence of seasonal dynamics on urban CH4 emissions.