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Obando, Bulacan, nestled in the heart of the Philippines, presents a unique geographic context influencing its air quality. Situated at 14.7083°N, 120.9375°E, the municipality occupies a low-lying area within the Central Luzon plain, characterized by relatively flat terrain. This proximity to Manila Bay, a significant body of water to the west, introduces maritime influences, but also potential for stagnant air masses. Obando’s landscape is a mosaic of residential areas, commercial establishments, and increasingly, agricultural lands – particularly rice paddies – reflecting its historical role as a fishing and farming community. The surrounding region is densely populated, forming part of Metro Manila’s sprawling urban conurbation. This proximity to a major metropolitan area is a key factor in air pollution transport. To the south and east lie more intensely urbanized areas and industrial zones within Bulacan and Metro Manila, contributing to regional pollution levels. The urban-rural gradient is relatively sharp, with agricultural areas bordering the built-up center. The low elevation and limited natural barriers mean Obando is particularly vulnerable to the accumulation of pollutants, especially during periods of calm weather. The Pasig River also flows nearby, potentially contributing to localised humidity and pollutant dispersion, but also acting as a conduit for pollutants from upstream sources.

Obando’s air quality follows a distinct wet and dry season pattern dictated by the Philippine monsoon. The dry season, typically from November to May, sees a marked increase in particulate matter (PM) and ozone due to increased temperatures, reduced rainfall for dust suppression, and stable atmospheric conditions. February to April are often the most challenging months, with stagnant air exacerbating pollution from vehicle emissions and nearby industrial activity. Conversely, the wet season, from June to October, brings relief. The southwest monsoon winds and frequent rainfall effectively wash pollutants from the atmosphere, leading to improved air quality. However, even during the wet season, localised flooding can stir up sediment and contribute to increased PM10 levels. Temperature inversions, common during the cooler, drier months, trap pollutants near the ground, worsening air quality. Fog, particularly in the early mornings during the dry season, can also exacerbate particulate matter concentrations. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during peak pollution periods in the dry season. Monitoring wind direction is crucial; winds from the south and east often carry pollutants from Metro Manila.