When you think of industrial pollution in Canada, Alberta's oil sands come to mind immediately. The federal data tell a different story. According to the National Pollutant Release Inventory (NPRI), the facility that reported the largest volume of releases between 2012 and 2024 is neither in Alberta nor in the oil sector. It's an aluminum smelter in Sept-Iles, Quebec.
Aluminerie Alouette, located in Sept-Iles on Quebec's North Shore, sits at the top of the rankings with 1 364 031 tonnes of cumulative releases between 2012 and 2024. The bulk of that volume comes from carbon monoxide (CO): 1.17 million tonnes, or 86% of the facility's total. The aluminum sector alone accounts for 45% of all CO releases reported to the NPRI across the country.
CO is a regulated air pollutant, but it differs from SO2 or heavy metals. It results from the incomplete combustion of carbon anodes used in electrolysis. Its health impact depends heavily on local concentration and dispersion. Directly comparing an aluminum smelter's CO tonnage to a nickel smelter's SO2 would be misleading. That said, the volume remains substantial and the fact stands: the facility that reports the most in the country is in Quebec.
Quebec, often associated with clean hydroelectric power, is actually home to several of the country's largest reporting facilities. Five Quebec aluminum smelters rank in the top 15: Alouette (1,364 kt), Usine Alma (896 kt), Aluminerie Becancour (682 kt), Usine Arvida (556 kt) and Aluminerie Baie-Comeau (550 kt). In total, Quebec recorded 10.9 million tonnes of releases between 2012 and 2024, from only 960 reporting facilities. The intensity per facility is the highest in the country.
Syncrude Canada (Fort McMurray) and Suncor Energy Oil Sands rank second and third with 1 138 956 and 1 125 830 cumulative tonnes, respectively. Their release profiles differ from aluminum: SO2, nitrogen oxides (NOx), particulate matter (PM) and volatile organic compounds (VOCs) dominate. These substances have direct effects on air quality and respiratory health.
Alberta remains the highest-emitting province in absolute volume: 14.6 million tonnes between 2012 and 2024. But that total is spread across thousands of reporting facilities, compared to 960 in Quebec for 10.9 million tonnes. The industrial structure is fundamentally different: thousands of wells, compressor stations and battery sites in Alberta, versus a few dozen heavy plants in Quebec.
Vale's Copper Cliff smelter in Sudbury, Ontario, accumulated 948 020 tonnes between 2012 and 2024. But the trajectory is striking: 152,000 tonnes in 2013, then 16,000 in 2024. An 85% reduction in SO2, achieved through the Clean AER (Atmospheric Emissions Reduction) project — a $1 billion investment over nine years, completed in 2021.
The key was capturing SO2 at the source rather than dispersing it through a tall stack. Vale installed new converters that contain sulphur gases inside the smelter, a wet gas cleaning plant that eliminates 85% of the captured SO2, and a baghouse that reduces metallic particulate emissions by 40%. Sudbury's famous Superstack — once a symbol of an era when pollution was dispersed rather than treated — was demolished in 2020. It had no more purpose: the SO2 never reached the chimney.
The chart below shows the 2012-2024 trajectory at Copper Cliff. The break is visible from 2017 onward, as the new equipment came progressively online. The aluminum smelters held steady. Syncrude and Suncor showed only marginal declines.
This did not happen voluntarily. Ontario's Ministry of the Environment had imposed strict SO2 limits with binding deadlines. Vale had no choice: invest or shut down. The company chose to invest, and the region the mining industry had devastated for decades is breathing better.
The contrast with Glencore's Fonderie Horne in Rouyn-Noranda, Quebec, is stark. The facility totalled 219 436 tonnes of cumulative releases between 2012 and 2024. A modest figure compared to the ranking's giants. But it is the nature of the releases that draws attention: 36 tonnes of arsenic released into the air in 2021 according to the NPRI, the highest level recorded since 2005 for this facility.
Glencore disputed the figure, citing contamination of the monitoring probe. The NPRI record was not amended. For years, the company lobbied Quebec to authorize an arsenic standard of 15 nanograms per cubic metre. Quebec set the threshold at 3 ng/m³. In February 2026, Glencore suspended its $300M investment in the facility and announced a demobilization plan. Without a deal, the smelter is heading toward closure in March 2027.
The parallel is blunt. Vale invested a billion dollars under Ontario's regulatory pressure and cut its emissions 85%. Glencore spent ten years in political negotiations instead of investing in the technology, and is losing its operating permit. The question is not whether the technology to reduce industrial releases exists. It does. The question is who holds the regulatory line.
Total releases reported to the NPRI in Canada fell from 3.7 million tonnes in 2012 to 2.86 million in 2024 (official data from Environment and Climate Change Canada). Some 7,887 facilities reported in 2024. The 19% reduction over 12 years is real, but at this pace, it would take over 30 more years to reach a 50% reduction.
SO2 saw the steepest decline, dropping from roughly 1,050 to 760 thousand tonnes (a 28% reduction). CO remained relatively stable, falling only 11%. NOx, PM and VOCs declined by 15 to 20%. The makeup of Canadian releases is shifting: SO2 is receding, but combustion-related pollutants (CO, NOx) persist.
Methodology: all data come from PollutionData's emissions table, filtered on entity_type='release' (NPRI), years 2012 to 2024. "All Media" rows were excluded. Units were normalized to tonnes (kg / 1,000; grams / 1,000,000). Provincial and facility totals are sums over the full period.
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