Author: Michelle Wan | Reviewer: David Clark, Licensed HVAC Technician | Publish Date: July 26, 2026| Updated Date: July 26, 2026

TL;DR

Longueuil sits on the south shore of the St. Lawrence River, directly across from Montreal, connected by the Jacques-Cartier Bridge and the Louis-Hippolyte-La Fontaine Bridge-Tunnel. Its air is measured by Quebec's provincial monitoring network, a separate system from the one the City of Montreal runs for stations on the island. Use the live map below for today's real-time Air Quality Health Index (AQHI) and Air Quality Index (IQA) reading rather than a number from memory, since both change hour to hour.

Key Takeaways

• Longueuil's air is tracked by Quebec's provincial network (RSQAQ), not the separate network the City of Montreal operates for its island stations, so a "Montreal" reading on some apps may not describe conditions on the South Shore.

• Canada's AQHI runs from 1 to 10+ and reflects combined short-term health risk from ozone, nitrogen dioxide, and fine particulate matter (PM2.5); Quebec's IQA runs from 0 into the hundreds and groups results into Bon, Acceptable, or Mauvais.

• Longueuil connects to Montreal's east end industrial corridor through two of the only five Saint Lawrence River crossings in the region, so bridge and tunnel traffic is a steady, local source of street-level pollution.

• On June 25, 2023, Environment Canada named Longueuil directly in a smog warning as wildfire smoke pushed the AQHI to 10+, a "very high risk" reading, across greater Montreal.

• Longueuil's furnace season runs roughly October through April; a fresh filter, like the MERV 8, 11, or 13 options Filterbuy Canada carries, matters most during the months your system works hardest.

• Check the live AQHI and IQA map above for today's number. Static articles like this one are built to explain what the number means, not to report it.

AQHI vs. IQA: Two Numbers for the Same Sky Above Longueuil

The AQHI is a health-risk index rather than a raw pollution measurement. It combines ground-level ozone, nitrogen dioxide, and fine particulate matter into a single number on a 1-to-10+ scale, weighted by each pollutant's known contribution to short-term health risk. Quebec's IQA works differently: it calculates a sub-index for each of five contaminants and reports the highest one as the hour's result, then sorts it into one of three categories.

One nuance worth knowing: Environment Canada's Info-Smog program issues AQHI forecasts for only three Quebec locations: Montreal, Quebec City, and Gatineau. Longueuil has no dedicated AQHI forecast, so residents checking it are really seeing the Montreal-area forecast used as a regional stand-in. The IQA, measured hour by hour at individual stations, can give a more local picture.

Categories and ranges reflect Quebec's Ministère de l'Environnement, de la Lutte contre les changements climatiques, de la Faune et des Parcs (MELCCFP) IQA methodology.

What to Actually Do at Each AQHI Level

Knowing the category is one thing. Knowing what to do with it is more useful, and it depends on whether you are generally healthy or at higher risk (children, people over 65, and anyone with a heart or lung condition).

Guidance reproduced from Environment and Climate Change Canada's official AQHI risk categories.

Two Air Networks, One River: Why Your Longueuil Reading Might Say "Montreal"

When we dug into where Longueuil's readings actually come from, we found a detail most air quality pages skip. Quebec's Réseau de surveillance de la qualité de l'air du Québec (RSQAQ) ran 66 monitoring stations province-wide in 2023: 55 operated by the Ministère and 11 by the City of Montreal, all on Montreal Island. Results from those island stations are excluded from the province's IQA map. Longueuil sits on the south shore, off the island, so it falls under the Ministère's provincial network rather than the city's system.

In practice, a weather app or aggregator that simply labels a reading "Montreal area" may be pulling from an island station, which is not the same monitoring authority as Longueuil's regional readings. If you live in Vieux-Longueuil, Saint-Hubert, or Greenfield Park, check a source that clearly identifies the South Shore or regional station rather than assuming an island number applies to your address.

Longueuil is also physically tied to Montreal's east end in a way that matters for air quality: two of the region's only five Saint Lawrence River crossings for vehicles, the Jacques-Cartier Bridge and the Louis-Hippolyte-La Fontaine Bridge-Tunnel, both land in Longueuil, funnelling steady traffic between the South Shore and Montreal's industrial east end. That corridor is a consistent, local contributor to street-level nitrogen dioxide and fine particulates, separate from whatever the regional background reading shows.

A Local Source Most Guides Miss: The Airport Inside Longueuil

Most write-ups on Longueuil's air stop at bridges and tunnels. There is a second local source worth knowing about: Montreal Metropolitan Airport (YHU), still widely known as Saint-Hubert Airport, sits inside Longueuil's Saint-Hubert borough rather than across the river. It logged 116,721 aircraft movements in 2023, ranking as Canada's 12th-busiest airport by that measure, and it is currently expanding toward a new terminal meant to handle up to four million commercial passengers a year.

None of that changes today's reading, but it explains why Saint-Hubert specifically can see localized traffic in the air that Vieux-Longueuil or Greenfield Park do not, on top of whatever the regional station shows. If you live near the airport corridor, that is one more reason to check a station-level reading rather than a single citywide number.

What Actually Moves the Needle in Longueuil, Season by Season

Longueuil's furnace season typically runs from October through April, among the longer heating seasons in the Filterbuy Canada service area, and that is also when indoor filtration works hardest to manage dust, dry winter air, and combustion byproducts pulled in around doors and windows.

Summer brings a different risk: wildfire smoke. Quebec's historic 2023 wildfire season pushed particulate levels across the province to their highest point in eight years, and on June 25, 2023, Environment Canada issued a smog warning that named Longueuil specifically, alongside Montreal, Laval, and Trois-Rivières, as the AQHI climbed to 10+, its "very high risk" category. Wildfire smoke season now runs roughly June through September and is worth tracking through SOPFEU's live wildfire map every summer, not just during major events.

Spring adds pollen to the mix, particularly for residents in the more residential Saint-Hubert and Greenfield Park boroughs, while Longueuil's dry winter air and humid summers both affect how efficiently any filter performs indoors.

Matching Your Filter to Longueuil's Conditions

Filterbuy Canada carries four filter types built around exactly these conditions. Here is how they line up with what the South Shore sees through the year:

The Filterbuy Canada Point of View

We build every city guide in this series the same way: by checking which monitoring agency actually covers the address, not just which big-name city sits nearby. Longueuil is a clear example of why that step matters.

We built our filter lineup around the idea that Canadians shouldn't have to choose between selection and simplicity. Longueuil households can order any of our 600-plus sizes with free shipping to Canada and prices shown in CAD, and our colour-coded MERV system makes it easy to know at a glance whether you have a Standard, Superior, or Optimal filter installed. During wildfire smoke season, many South Shore households step up to a MERV 13 filter. Subscribe and save lets you time deliveries to furnace season or smoke season, and you can edit or cancel anytime.

In  a place like Longueuil, where you've got a long furnace season and river crossings funnelling traffic right past residential streets, I tell homeowners not to fixate on one number. Check the live reading before you plan strenuous outdoor time, and match your filter to the season you're actually in, not the season you bought it in." - David Clark, Licensed HVAC Technician, Filterbuy HVAC Solutions

Essential Resources for Cleaner Air in Longueuil

Check today's official air quality reading

Quebec's Ministère de l'Environnement publishes an hourly, province-wide IQA map, and Environment Canada maintains alerts for the Longueuil - Varennes area specifically.

Understand your filter's MERV rating before you buy

Not sure what Standard, Superior, or Optimal means for your home? This Filterbuy Canada guide breaks down every rating we carry.

Track wildfire smoke risk before it reaches the South Shore

Quebec's forest fire agency, SOPFEU, posts real-time fire activity and danger ratings, giving Longueuil households advance notice before smoke arrives.

Get the right filter delivered on your schedule

Browse Filterbuy Canada's air filter subscription for free shipping to Canada and a schedule you can adjust anytime the season changes your needs.

Supporting Statistics

The smoke behind Longueuil's June 2023 warning did not stop at the border. U.S. federal and public health data confirm the scale:

1. 17% spike in asthma ER visits. Emergency visits for asthma rose 17% above normal during the 19 smokiest days of the 2023 Canadian wildfires (April 30 to August 4, 2023). Source: CDC, MMWR (cdc.gov).

2. 37+ million Americans exposed in one event. A 2025 Canadian wildfire event pushed air quality to "Unhealthy for Sensitive Groups" or worse for over 37 million people, including 9+ million at "Unhealthy." Source: U.S. Census Bureau (census.gov).

3. 77.2 million people, a 16-year high. The American Lung Association's 2025 report found 77.2 million people living in U.S. counties with unhealthy short-term particle pollution spikes, the highest count in 16 years, driven partly by that same 2023 smoke. Source: American Lung Association (lung.org).

The pattern repeats across events, not just 2023. That consistency is why filtration planning matters year to year, not just during headline smoke days.

Glossary

AQHI (Air Quality Health Index): Canada's official 1-to-10+ scale combining ozone, nitrogen dioxide, and fine particulate matter into a single short-term health risk number.

IQA (Indice de la Qualité de l'Air): Quebec's provincial air quality index, which reports the highest of five pollutant sub-indices for a station and sorts it into Bon, Acceptable, or Mauvais.

PM2.5: Fine particulate matter measuring 2.5 micrometres or smaller in diameter, small enough to be inhaled deeply into the lungs; a major driver of both the AQHI and the IQA during wildfire smoke events.

RSQAQ: Réseau de surveillance de la qualité de l'air du Québec, the provincial monitoring network, distinct from the City of Montreal's network.

MELCCFP: Quebec's Ministère de l'Environnement, de la Lutte contre les changements climatiques, de la Faune et des Parcs, the provincial ministry responsible for the RSQAQ and the IQA.

MERV: Minimum Efficiency Reporting Value, a scale describing how effectively a filter captures particles. See Filterbuy Canada's MERV ratings guide.