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Ragan Sur, nestled in the province of Isabela, Philippines, occupies a strategically important position within the Cagayan Valley region. Located at approximately 17.32° N, 121.78° E, the city’s geography is characterized by a gently undulating terrain, typical of the fertile alluvial plains formed by the Magat River and its tributaries. The surrounding landscape is predominantly agricultural, a patchwork of rice paddies, cornfields, and smaller farms, reflecting Isabela’s status as a major agricultural producer. This proximity to intensive farming practices contributes to localized air quality concerns, particularly related to agricultural burning during land preparation. Ragan Sur’s elevation is relatively low, averaging around 150 meters above sea level, which can exacerbate the trapping of pollutants, especially during periods of stable atmospheric conditions. The city benefits from its access to the Magat River, providing a crucial water source and influencing local humidity levels. While not directly coastal, the region’s overall climate is tropical, with distinct wet and dry seasons. The urban character of Ragan Sur is primarily rural-urban transitional; it’s a small municipality experiencing gradual growth, with a mix of residential areas, small businesses, and agricultural support services. The urban–rural gradient is relatively smooth, with agricultural land extending almost seamlessly into the city limits. The regional position, within a major agricultural belt, means that air quality is intrinsically linked to agricultural activities and broader regional weather patterns, making it susceptible to transboundary pollution events from neighboring provinces.

Ragan Sur’s air quality follows a predictable seasonal pattern dictated by the Philippines’ tropical climate. The wet season, typically spanning from June to November, brings frequent rainfall and generally improved air quality. The consistent precipitation effectively washes away particulate matter and reduces the concentration of gaseous pollutants. However, periods of prolonged rainfall can also lead to increased humidity, which can exacerbate respiratory issues for sensitive individuals. Conversely, the dry season (December to May) presents a greater air quality challenge. Reduced rainfall, coupled with higher temperatures, leads to increased evaporation and the formation of photochemical smog, particularly during the hottest months of April and May. Calm wind conditions are common during this period, promoting the build-up of pollutants. Temperature inversions, where a layer of warm air sits above cooler air near the ground, are also more frequent, trapping pollutants close to the surface. Agricultural burning, a common practice in the surrounding farmlands to clear fields for planting, significantly contributes to particulate matter pollution during the dry season, often peaking in March and April. The monsoon season, specifically the northeast monsoon (Amihan), can bring periods of cleaner air in late December and January, but also occasional dust storms from the northeast. Sensitive groups, including children, the elderly, and individuals with pre-existing respiratory conditions, should exercise caution during the dry season, limiting outdoor activities during peak pollution hours and ensuring adequate ventilation indoors. Periods of heavy rainfall offer a respite, but humidity management remains important.