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Saint John, New Brunswick, occupies a uniquely exposed position on the northern edge of the Bay of Fundy, a location profoundly shaping its air quality. The city is built on a series of hills overlooking the harbour, a natural deep-water port that has historically driven its economic development. This coastal setting, while advantageous for trade, also means Saint John is directly exposed to prevailing winds carrying pollutants from both marine sources and across the Atlantic. The surrounding landscape is a mix of forested hills, agricultural land in the Kennebecasis Valley to the northwest, and the extensive mudflats of the Bay of Fundy. Historically, the city’s industrial sector, concentrated along the waterfront, contributed significantly to local emissions, though efforts have been made to modernize and reduce pollution. The urban-rural gradient is relatively sharp; moving inland quickly transitions from the denser city core to more sparsely populated, forested areas. Elevation changes within the city itself, combined with the maritime climate, can create localized microclimates and influence pollutant dispersion. The proximity to the ocean moderates temperatures but also contributes to high humidity and fog, which can trap pollutants near the ground. This geographic configuration makes Saint John particularly sensitive to long-range transport of pollutants and local emission sources.

Saint John’s air quality follows a distinct seasonal pattern. Winter months, from December to February, often see poorer air quality due to temperature inversions – a common phenomenon in the Bay of Fundy region where cold air becomes trapped beneath warmer air, concentrating pollutants. Wood burning for heating contributes to particulate matter during these months. Spring brings a gradual improvement as temperatures rise and winds increase, dispersing pollutants. However, snowmelt can release accumulated contaminants. Summer generally offers the best air quality, with prevailing winds effectively flushing out the harbour area. However, occasional stagnant air masses can lead to localized pollution build-up. Autumn sees a return to more variable conditions, with increasing wood smoke as heating season approaches. Fog, frequent throughout the year, particularly in spring and fall, can exacerbate pollution by trapping pollutants. Sensitive individuals, such as those with respiratory conditions, should be particularly cautious during winter inversions and periods of dense fog. Monitoring wind patterns and avoiding strenuous outdoor activity on still, cold days is advisable. The months of July and August typically offer the most favourable conditions for outdoor recreation.