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Montreal's Hidden Climate Culprit: The Surprising Source Choking Our Air

  • MM24 News Desk
  • Oct 19
  • 3 min read
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We picture city pollution as a haze of car exhaust and factory smoke. But what if one of the biggest threats to our climate is invisible, odorless, and rising from places we'd never expect? Groundbreaking research from McGill University is pulling back the curtain on Montreal’s methane emissions, and the map of culprits is full of surprises. Forget what you thought you knew about urban pollution; the reality is far more uneven and puzzling.


For four years, scientists embarked on a city-wide scavenger hunt, not for treasure, but for an invisible gas. They drove and even biked across 3,300 square kilometres of Montreal, armed with sensitive equipment that sniffed the air every single second. Their mission? To pinpoint exactly where methane, a potent greenhouse gas, was escaping into our atmosphere. What they found challenges our assumptions about where urban pollution truly lurks.


So, why all the fuss about methane? While carbon dioxide (CO2) often steals the headlines, methane is the climate crisis's silent heavyweight. As Professor Peter Douglas, a co-author of the study, explains, "Though there's much less methane than carbon dioxide in the atmosphere, every methane molecule will warm the planet by about 32 times as much as every CO2 molecule." It’s a concentrated punch to the planet’s warming potential, which is precisely why finding its sources is so critical. We can't fix what we can't see.




The findings paint a stark picture of a city divided. The highest concentrations of this invisible gas are overwhelmingly concentrated in Montreal's east end. But the identity of the top polluters is where the story gets truly fascinating. While inactive landfills, like the massive Parc Frédéric-Back site, were expected to be major emitters, researchers got a shock from another source: the Francon Quarry. This site, home to the city's largest snow dump, was found to be emitting methane at a rate comparable to the landfills.



Think about that for a second. A place where we pile snow is producing a greenhouse gas on par with decades-old dumping grounds. How is that possible? Professor Douglas clarifies that it’s not just the snow. "A ton of stuff is dumped there, stuff that’s picked up off the roads," he notes. As the massive snow pile melts, it creates a soupy, oxygen-poor lake where microbes thrive, feasting on the organic waste and releasing methane as a byproduct. It's an unintended environmental consequence of a routine city service.


The east end’s problem is a double whammy. In addition to hosting a legacy of former landfills, it’s also where the city’s older natural gas infrastructure is most prone to leaks. "Most gas leaks are concentrated where we use this older infrastructure," Douglas confirms. More people mean more gas lines and, inevitably, more unintended escapes. Over the course of the study, the team identified more than 3,000 of these methane hotspots across the island.



While this number is lower than in some similarly dense cities, each one represents a potent and preventable source of warming. The repeated weekly surveys along set routes allowed the team to distinguish between fleeting leaks and persistent, chronic emitters. By combining real-time gas measurements with wind data, they could literally triangulate the source, turning a vague cloud of gas into a precise address for action.


This isn't just an academic exercise. It's a crucial step toward Quebec's ambitious goal of reducing greenhouse gas emissions by 37.5 per cent by 2030. You can't manage what you don't measure, and this robust, street-level data provides a clear roadmap for the city. The work continues, with future plans to track seasonal variations and even explore how bacteria at landfill surfaces might help consume some of the gas. For now, the message is clear: tackling climate change means looking beyond the obvious and addressing the hidden emissions right under our feet.



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