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Ilagan City, nestled in the heart of Isabela province, Philippines, occupies a strategically important position within the Cagayan Valley region. Its coordinates (17.1489° N, 121.8894° E) place it within a predominantly lowland landscape, characterized by fertile alluvial plains formed by the Cagayan River and its tributaries. The city’s terrain is gently undulating, transitioning from flat agricultural lands to the foothills of the Sierra Madre mountain range to the east. This proximity to the Sierra Madre, the longest mountain range in the Philippines, significantly influences local weather patterns and air circulation. Ilagan sits approximately 145 meters above sea level, contributing to a relatively moderate climate. The surrounding landscape is overwhelmingly rural, dominated by extensive rice paddies, cornfields, and banana plantations – key agricultural drivers for the local economy. This strong agricultural presence, while vital for livelihoods, introduces potential sources of air pollutants, particularly from fertilizer use and occasional field burning. The urban–rural gradient is gradual, with pockets of residential development interspersed within the agricultural matrix. While Ilagan is the regional center for Isabela, it retains a distinctly provincial character, lacking the dense industrial belts found in larger metropolitan areas. The Magat Dam, a significant hydroelectric facility, lies to the north, influencing regional water resources and potentially contributing to localized humidity and fog formation. The prevailing winds generally flow from the east, bringing moisture from the Pacific Ocean, impacting air quality through humidity and potential for rainfall-driven pollutant removal.

Ilagan’s tropical climate dictates a distinct wet and dry season, profoundly impacting its air quality profile. The dry season, typically spanning from November to May, often sees a gradual accumulation of pollutants. Reduced rainfall during this period limits the natural cleansing effect of precipitation, allowing particulate matter and gaseous pollutants to linger. Temperature inversions, common during the cooler months (December-February), trap pollutants near the ground, exacerbating localized air quality concerns. Agricultural activities intensify during this period, with increased fertilizer application and, occasionally, controlled burning of crop residues, contributing to emissions. The wet season, from June to October, brings frequent rainfall and increased humidity, generally leading to improved air quality as pollutants are washed away. However, heavy rainfall can also lead to flooding, which can temporarily release pollutants from inundated areas. Monsoon winds, particularly during August and September, can bring moisture and occasional dust from neighboring regions, impacting air quality. Fog, particularly prevalent during the cooler, drier months, can trap pollutants, reducing visibility and increasing exposure. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly during periods of stagnant air or fog. Outdoor activities are generally more favorable during the wet season, although vigilance regarding potential flooding is advised. The intensity of agricultural practices and the frequency of controlled burns are key factors influencing air quality fluctuations throughout the year, demanding careful monitoring and mitigation strategies.