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Sual, Pangasinan, Philippines, occupies a strategically important coastal location on the Lingayen Gulf, a significant inlet of the South China Sea. Situated at approximately 16.0661° N, 120.0958° E, the town’s geography is characterized by a gently sloping terrain transitioning from the coastal plains to slightly elevated inland areas. The elevation rarely exceeds 50 meters above sea level, contributing to a relatively flat urban landscape. This low elevation, combined with its proximity to the Gulf, makes Sual susceptible to sea breezes and coastal fog, which can significantly influence local air circulation patterns. The surrounding landscape is a mix of agricultural land – primarily rice paddies and coconut plantations – and small-scale fishing communities. To the east, the Zambales Mountains rise, providing a partial barrier to prevailing winds from the west. The urban–rural gradient is gradual, with agricultural activities seamlessly blending into the town’s residential and commercial areas. Sual’s coastal location also positions it near industrial zones concentrated in nearby Dagupan City, potentially exposing it to transboundary pollution. The presence of the Sual Coal-Fired Power Plant, a major energy provider for Luzon, is a defining feature of the landscape and a key factor impacting local air quality. The town’s geography, therefore, presents a complex interplay of natural ventilation, agricultural emissions, and industrial influences, all shaping its atmospheric conditions.

Sual’s tropical climate dictates a distinct wet and dry season, profoundly influencing its air quality profile. The dry season, typically spanning from November to May, often sees a slight improvement in air quality due to increased wind speeds and solar radiation, which aids in pollutant dispersion. However, this period can also experience periods of stagnant air, particularly during anticyclonic conditions, leading to localized pollutant build-up. The wet season, from June to October, brings monsoon rains and increased humidity. While rainfall naturally scavenges pollutants from the atmosphere, the associated cloud cover reduces solar radiation, hindering photochemical reactions that break down some pollutants. Fog, common during the transition months (November and March), traps pollutants near the ground, exacerbating respiratory issues. Agricultural burning, a common practice during the dry season to clear fields for planting, contributes significantly to particulate matter pollution. The Sual Power Plant’s operations remain relatively consistent throughout the year, but its emissions can be more noticeable during periods of reduced wind and increased fog. Sensitive groups, such as children, the elderly, and individuals with pre-existing respiratory conditions, should exercise caution during periods of agricultural burning and fog, limiting outdoor activities and ensuring adequate ventilation. The months of April and May, coinciding with peak agricultural activity, often present the greatest air quality challenges, while December and January, with clearer skies and more consistent winds, generally offer the most favourable conditions for outdoor pursuits.