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San Juan de Dios, nestled within the San José province of Costa Rica, occupies a geographically significant position within the Central Valley. Located at approximately 9.88° latitude and -84.09° longitude, the district sits at an elevation of roughly 1150 meters (3773 feet) above sea level, placing it firmly within a subtropical highland environment. The surrounding landscape is characterized by a mix of rolling hills, agricultural land, and patches of secondary forest, typical of the Costa Rican interior. The Central Valley itself is a broad, fertile basin ringed by volcanic mountain ranges, influencing regional weather patterns and air circulation. San Juan de Dios benefits from proximity to the Virilla River, though its direct impact on local air quality is minimal. The urban–rural gradient shifts rapidly; the district borders more rural areas, with small farms and coffee plantations visible within a short distance. While San José, the national capital, lies just a few kilometers to the south, San Juan de Dios retains a more residential character, with lower population density than the core urban area. The valley's topography, combined with the prevailing easterly trade winds, can create localized air stagnation, particularly during periods of reduced wind speed. Industrial activity is concentrated further towards San José, but vehicular traffic from commuters contributes to local air pollution. The volcanic soils, while fertile, can also contribute to dust particulate matter, especially during the dry season when vegetation cover is reduced.

San Juan de Dios experiences a tropical climate with distinct wet and dry seasons, significantly impacting air quality dynamics. The dry season, typically from December to April, often sees a reduction in rainfall and an increase in sunshine hours. However, this period frequently coincides with elevated particulate matter concentrations. Reduced rainfall means less atmospheric cleansing, and the drier conditions encourage dust generation from unpaved roads and agricultural activities. Temperature inversions, where a layer of warm air traps cooler air near the ground, are more common during the dry season, hindering vertical mixing and concentrating pollutants. The wet season, from May to November, brings increased rainfall, which naturally washes pollutants from the atmosphere, leading to improved air quality. However, heavy rainfall can also mobilize soil particles, temporarily increasing particulate matter. Fog, common during the wet season, can trap moisture and pollutants near the ground, creating localized pockets of reduced visibility and potentially impacting respiratory health. Months like February and March, within the dry season, often present the most challenging conditions for air quality. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should limit prolonged outdoor exertion during these periods. During the wet season, while overall air quality improves, periods of intense rainfall and subsequent soil disturbance can warrant temporary precautions. Maintaining vehicle maintenance and minimizing dust-generating activities are crucial year-round to mitigate local air pollution.