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L’Ancienne-Lorette, nestled within the Quebec City metropolitan area, occupies a geographically significant position in the St. Lawrence Lowlands. The municipality’s terrain is characterized by rolling hills and valleys, a legacy of glacial activity that sculpted the landscape during the last ice age. Situated approximately 6 kilometers northeast of downtown Quebec City, it benefits from the region’s generally temperate climate, moderated by the proximity of the St. Lawrence River. This river, a major waterway, influences local weather patterns and contributes to humidity levels. The surrounding landscape is a blend of urban and rural elements; L’Ancienne-Lorette exhibits a gradual urban–rural gradient, transitioning from residential areas to agricultural fields and forested patches. While not directly adjacent to major industrial zones, its location within the broader Quebec City region means it’s indirectly influenced by industrial emissions originating from the city center and surrounding areas. The elevation varies, generally ranging from 150 to 250 meters above sea level, which can impact local air circulation patterns, potentially trapping pollutants under certain meteorological conditions. The Laurentian Mountains lie to the north, influencing prevailing wind directions and occasionally contributing to cold air advection. The relatively flat topography of the lowlands, combined with the valley formations, can create localized areas of stagnant air, particularly during periods of calm weather, impacting air quality within the municipality. The presence of agricultural land nearby introduces potential sources of particulate matter, particularly during planting and harvesting seasons.

L’Ancienne-Lorette’s air quality experiences a distinct seasonal cycle driven by meteorological factors. Spring (March-May) often brings a gradual improvement as snow cover recedes, and temperatures rise, increasing atmospheric mixing and dispersing pollutants. However, agricultural activities, including tilling and fertilizer application, can temporarily elevate particulate matter levels. Summer (June-August) generally sees good air quality, with frequent breezes from the St. Lawrence River helping to ventilate the area. However, periods of hot, stagnant air can occur, particularly during heatwaves, leading to the formation of ground-level ozone, a respiratory irritant. Autumn (September-November) presents a mixed picture. Cooler temperatures and stable atmospheric conditions can lead to temperature inversions, trapping pollutants near the ground, especially in the mornings. Leaf burning, a traditional practice, can also contribute to localized smoke pollution. Winter (December-February) is often the most challenging season. Cold air masses, coupled with temperature inversions, frequently trap pollutants, leading to periods of reduced air quality. Snow cover can also contribute to the buildup of particulate matter. Fog, common during winter mornings, further exacerbates the issue by reducing visibility and trapping pollutants. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should limit prolonged outdoor exertion during periods of stagnant air or fog, particularly in the mornings. Monitoring local weather forecasts and air quality reports is crucial for making informed decisions about outdoor activities throughout the year.