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Sainte-Anne-des-Plaines, Quebec, occupies a strategically important position within the Laurentian foothills, approximately 30 kilometers north of Montreal. Its coordinates (45.7617, -73.8204) place it on relatively gently sloping terrain, transitioning from the relatively flat St. Lawrence Lowlands to the more rugged landscape of the Laurentian Mountains. The city’s proximity to the Rivière des Prairies, a significant waterway connecting Lake of Two Mountains to the St. Lawrence River, influences local microclimates and contributes to humidity levels. The surrounding landscape is a blend of agricultural land, particularly dairy farms and crop fields, and increasingly, suburban development extending outwards from Montreal. This urban–rural gradient means Sainte-Anne-des-Plaines experiences a mix of rural and urban influences. While not directly within a major industrial belt, its location within the Montreal metropolitan area exposes it to secondary pollution transport from the city’s industrial zones and transportation corridors. The elevation, averaging around 150 meters above sea level, is not particularly high, but the Laurentian foothills to the north can create localized temperature inversions, particularly during colder months, trapping pollutants closer to the ground. The prevailing winds generally flow from the northwest, carrying potential pollutants from across the region. The presence of agricultural activity introduces potential sources of ammonia and particulate matter, while the ongoing suburban expansion contributes to increased vehicle traffic and associated emissions. The city’s geography, therefore, presents a complex interplay of factors impacting air quality.

Sainte-Anne-des-Plaines experiences a distinct four-season climate, and this profoundly shapes its air quality profile. Winter (December – February) often sees the most challenging conditions. Cold, stable air masses frequently lead to temperature inversions, where a layer of warm air sits above cooler air near the ground, preventing vertical mixing and trapping pollutants. This, combined with reduced sunlight hours and limited wind, can result in stagnant air and elevated concentrations of particulate matter and other pollutants. Spring (March – May) brings a gradual improvement as temperatures rise and winds increase, dispersing pollutants. However, agricultural activities, such as fertilizer application, can contribute to ammonia emissions. Summer (June – August) generally offers the best air quality, with warm temperatures, frequent thunderstorms, and strong winds that effectively flush out pollutants. However, hot, humid days can sometimes lead to ozone formation, a secondary pollutant. Autumn (September – November) presents a transitional period. Cooler temperatures and calmer winds can occasionally lead to localized pollution episodes, particularly as leaves decompose and contribute to particulate matter. Fog, common in the autumn mornings, can also trap pollutants near the ground. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should be particularly mindful during winter inversions and periods of agricultural activity. During summer heatwaves, limiting strenuous outdoor activity during peak ozone hours is advisable. Overall, the city’s air quality follows a seasonal cycle dictated by meteorological conditions and local activities.