Snow dump and inactive landfills flagged as major methane polluters

McGill University researchers have uncovered startling disparities in methane emissions across Montreal, with the city’s east end bearing the heaviest pollution burden. The comprehensive four-year mobile monitoring survey identified over 3,000 methane hotspots, revealing that inactive landfills and an unexpected culprit—the city’s largest snow dump—are emitting methane at alarming rates comparable to current and former waste facilities. This groundbreaking research, published in Environmental Research Communications, provides crucial data to help Quebec achieve its ambitious goal of reducing greenhouse gas emissions by 37.5% by 2030. The findings align with recent comprehensive analysis of urban methane patterns that highlight the urgent need for targeted mitigation strategies.

“Though there’s much less methane than carbon dioxide in the atmosphere, every methane molecule will warm Earth by about 32 times as much as every CO₂ molecule,” emphasized Peter Douglas, Associate Professor in McGill’s Department of Earth and Planetary Sciences and co-author of the study. “We need to know where these emissions are coming from to resolve them.” Unlike annual emissions inventories that rely on estimates, this mobile monitoring campaign gathered robust, real-time data through systematic surveys across 3,300 square kilometers of urban landscape.

Surprising Polluters: From Snow Dumps to Dormant Landfills

The research team made several unexpected discoveries that challenge conventional understanding of urban methane sources. While inactive landfills—including major urban renewal projects like Parc Frédéric-Back—produced the highest emissions, the Francon Quarry, which serves as Montreal’s primary snow dump, emerged as a methane source of comparable significance.

“It’s as large as some of the other landfills,” Douglas noted. “A ton of stuff is dumped there, material that’s picked up off the roads.” As accumulated snow melts, it creates temporary lakes that harbor methane-producing microbes, transforming what might appear as benign winter maintenance into a significant climate concern. This finding underscores how urban infrastructure decisions can have unintended environmental consequences, much like how molecular structures determine environmental interactions in complex systems.

Geographic Disparities and Infrastructure Challenges

The spatial distribution of methane emissions reveals troubling patterns of environmental inequality. Montreal’s east end consistently showed the highest methane concentrations, a region that hosts numerous former landfills while also suffering from aging natural gas infrastructure.

“Most gas leaks are concentrated where we use this older infrastructure,” Douglas explained. “But we really focused on population density. With more people, there are more natural gas lines and more leaks.” This connection between urban density, aging infrastructure, and emissions highlights the complex interplay between urban development and environmental impact—a challenge that extends beyond methane to how systemic approaches can address complex problems across different domains.

Innovative Methodology and Seasonal Monitoring

The research team employed sophisticated mobile monitoring techniques, conducting surveys over multiple years (2019, 2022-2024) across Greater Montreal and key off-island locations like the Saint-Sophie landfill. Using devices that measured carbon dioxide and methane levels every second, researchers collected precise atmospheric data while navigating the urban landscape.

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Three fixed routes—two in densely populated areas and one near the Lachine Canal—were surveyed weekly for 10 weeks, allowing researchers to track how methane emissions fluctuated over time. “We’d see an increase in concentration and then it would come back down, so we could figure out approximately how much gas was coming from that source and locate where it was,” Douglas described, noting that wind data helped triangulate emission sources with remarkable accuracy.

The collaborative nature of the project involved Environment and Climate Change Canada conducting much of the vehicle-based testing, while local bikeshare service BIXI provided free memberships to facilitate the research—demonstrating how community partnerships can advance scientific understanding.

Broader Environmental Implications

The Montreal methane study contributes to growing evidence that urban environments play a significant role in greenhouse gas emissions that extend beyond typical industrial sources. The persistence of methane hotspots, particularly from snow dumps and inactive landfills, suggests that cities must develop more comprehensive monitoring and mitigation strategies.

As the research continues, the team plans to track seasonal variations in methane concentrations and investigate whether surface bacteria at landfill sites might naturally mitigate some emissions. This approach recognizes that environmental solutions often require understanding complex ecological relationships, similar to how ecosystem vulnerabilities demand integrated conservation strategies.

The findings underscore the importance of moving beyond estimated emissions inventories toward direct measurement campaigns that can identify specific pollution sources. As cities worldwide grapple with climate commitments, the Montreal study offers both a methodology and a warning: hidden emissions from unexpected sources could undermine environmental progress without targeted intervention and continuous monitoring.