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San Bernardo, Nariño, Colombia, nestled within the Andean foothills, presents a unique geographic profile significantly influencing its air quality. Located at approximately 1.5108° latitude and -77.0467° longitude, the municipality sits at a considerable elevation, averaging around 2,100 meters (6,889 feet) above sea level. This high altitude contributes to cooler temperatures and a generally thinner atmosphere, which can affect pollutant dispersion. The surrounding landscape is dominated by steep slopes, dense cloud forests, and agricultural terraces, characteristic of the Andean region. San Bernardo’s position within the department of Nariño places it near the border with Ecuador, within a region known for its biodiversity and complex topography. The municipality’s urban character is primarily rural, with a small, concentrated population of 21,492. Agriculture, particularly coffee cultivation and livestock farming, forms the backbone of the local economy, introducing potential sources of particulate matter and ammonia into the air. While San Bernardo isn't directly adjacent to major industrial belts, its proximity to larger towns and cities in Nariño means it can be affected by transboundary pollution. The urban–rural gradient is sharp; the town itself is relatively compact, transitioning quickly into agricultural lands and forested areas. The terrain’s steepness limits air circulation, potentially trapping pollutants, while the cloud forests can contribute to fog formation, further hindering dispersion and exacerbating air quality challenges, especially during periods of low wind speed. The lack of significant water bodies nearby also reduces natural air cleansing mechanisms.

San Bernardo’s tropical highland climate dictates a distinct wet and dry season pattern, profoundly impacting its air quality. The wet season, typically spanning from April to October, brings frequent rainfall and increased humidity. While precipitation naturally helps to cleanse the atmosphere by washing away particulate matter, the increased moisture can also lead to the formation of fog, particularly in the mornings, which traps pollutants close to the ground. Agricultural activities intensify during this period, with increased burning of vegetation for land clearing and fertilizer application, contributing to localized spikes in smoke and ammonia. The dry season, from November to March, is characterized by lower rainfall and higher temperatures. This often results in temperature inversions, where a layer of warm air sits above cooler air near the ground, preventing vertical mixing and trapping pollutants. Reduced wind speeds during this time further exacerbate the problem. The combination of these factors can lead to periods of stagnant air and elevated levels of particulate matter. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly during mornings when fog is prevalent. Outdoor activities are generally more favorable during the wet season, although caution should be taken regarding potential landslides due to heavy rainfall. Agricultural workers should be mindful of exposure to smoke and fertilizers, utilizing appropriate protective equipment.