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San Narciso, Zambales, nestled on the western coast of Luzon Island in the Philippines, occupies a geographically significant position within the Central Luzon region. Its coordinates (15.0200° N, 120.0800° E) place it directly facing the South China Sea, a defining characteristic influencing its climate and, consequently, its air quality. The municipality’s terrain is predominantly undulating, transitioning from coastal plains to gently sloping hills, rising to approximately 150 meters above sea level in its inland areas. This varied topography can influence local wind patterns and the dispersion of pollutants. San Narciso is surrounded by a mosaic of landscapes: to the west, the expansive South China Sea; to the east, agricultural lands and small-scale farms cultivating crops like rice and mangoes; and inland, gradually rising hills covered in secondary forests. The urban character is relatively low-density, a blend of residential areas, small commercial establishments, and agricultural support services. The urban–rural gradient is gradual, with agricultural activities seamlessly integrating into the town’s periphery. While not directly adjacent to major industrial belts, San Narciso’s proximity to Subic Bay Freeport Zone, approximately 30 kilometers to the north, introduces a potential source of industrial emissions that can be transported by prevailing winds. The coastal location also means the town is susceptible to sea salt aerosol deposition, which can impact visibility and contribute to particulate matter in the air. The town’s location within the Zambales mountain range’s rain shadow also influences precipitation patterns, potentially impacting atmospheric cleansing processes.

San Narciso experiences a tropical climate characterized by distinct wet and dry seasons, significantly impacting its air quality profile. The dry season, typically spanning from November to May, often sees a relative improvement in air quality due to increased solar radiation and drier conditions, promoting atmospheric mixing and pollutant dispersion. However, this period can also be punctuated by periods of stagnant air, particularly during temperature inversions, where cooler air becomes trapped beneath a layer of warmer air, hindering vertical mixing and concentrating pollutants near the ground. The wet season, from June to October, brings frequent rainfall and increased humidity. While rainfall naturally helps to scrub pollutants from the atmosphere, the associated cloud cover can reduce solar radiation, potentially leading to reduced atmospheric mixing and localized pockets of poorer air quality. The southwest monsoon (Habagat) strongly influences this period, bringing consistent winds from the southwest, which generally disperse pollutants offshore. However, periods of weaker winds can lead to pollutant accumulation. Fog, particularly during the transition months (November and May), can also trap pollutants, reducing visibility and impacting air quality. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during periods of stagnant air or fog, limiting prolonged outdoor exposure. Agricultural burning, a common practice during the dry season to clear fields, can also contribute to localized spikes in particulate matter. The months of April and May, coinciding with the end of the dry season and the onset of the wet season, often present a transitional period with variable air quality conditions.