Vigan Air Quality Index (AQI)

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Vigan, a UNESCO World Heritage city nestled in the province of Ilocos Sur, Philippines, occupies a unique geographic position that significantly influences its air quality. Situated at approximately 17.57°N, 120.39°E and an elevation of around 24 meters (79 feet) above sea level, Vigan lies on a gently sloping alluvial plain formed by the Abra River and its tributaries. This low-lying terrain, coupled with its proximity to the West Philippine Sea, creates a coastal environment susceptible to maritime influences. The surrounding landscape is a blend of agricultural lands – primarily rice paddies and cornfields – and rolling hills, characteristic of the Ilocos region. The urban–rural gradient transitions smoothly, with agricultural activities occurring within a relatively short distance of the city center. While Vigan itself is not a major industrial hub, it serves as a regional commercial center, with some light industries and workshops present, contributing localized pollution sources. The Abra River, while providing a vital water source, can also act as a conduit for pollutants from upstream agricultural runoff. The prevailing winds generally blow from the west, carrying moisture and potential pollutants from the sea. Topographically, the lack of significant elevation changes limits natural air dispersion, potentially trapping pollutants under certain meteorological conditions. The city’s compact urban core, characterized by historic Spanish colonial architecture and narrow streets, can also contribute to localized air quality challenges, particularly from vehicle emissions and cooking fumes.

Vigan’s tropical climate dictates a distinct wet and dry season, profoundly impacting its air quality profile. The dry season, typically spanning November to May, often sees clearer skies and reduced rainfall, but also heightened concerns regarding particulate matter. During these months, particularly March and April, the lack of rainfall allows dust and emissions to accumulate, potentially leading to poorer air quality. Temperature inversions, common during the cooler nights of the dry season, can trap pollutants close to the ground, exacerbating the issue. The wet season, from June to October, brings frequent rainfall and increased humidity. These conditions naturally cleanse the atmosphere, washing away particulate matter and reducing overall pollution levels. However, the monsoon season (July-September) can introduce moisture and, occasionally, dust from distant sources, impacting visibility and potentially triggering respiratory sensitivities. Fog, a relatively infrequent occurrence, can also trap pollutants, creating localized pockets of poor air quality. Outdoor activities are generally more favorable during the wet season, especially during the months of August and September when rainfall is consistent. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly during periods of prolonged dry weather and potential temperature inversions. Minimizing exposure to traffic and enclosed spaces with poor ventilation is advisable during these times. The agricultural burning practices common in surrounding rural areas during the dry season can also contribute to localized air pollution events, impacting Vigan’s air quality.