San Juan Air Quality Index (AQI)

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San Juan, a highly urbanized city within Metro Manila, Philippines, occupies a relatively small area of 5.91 square kilometers. Its geographic position is crucial to understanding its air quality challenges. Situated on a low-lying plain, the city’s elevation rarely exceeds 20 meters above sea level, making it susceptible to ground-level ozone formation and trapping of pollutants. San Juan is bordered by Quezon City to the north, Mandaluyong City to the east, Makati City to the south, and Caloocan City to the west, placing it squarely within the densely populated and industrialized heart of Metro Manila. The Pasig River flows nearby, though its impact on air quality is complex – while it can sometimes facilitate pollutant dispersion, it also contributes to humidity, which can exacerbate ozone formation under certain conditions. The surrounding landscape is overwhelmingly urban, characterized by concrete structures, roadways, and commercial establishments. There's a minimal urban-rural gradient; San Juan is entirely urbanized, lacking significant agricultural zones within its boundaries. However, the broader Metro Manila region includes agricultural areas further out, which can contribute to particulate matter transport, particularly during dry seasons. The city’s proximity to major industrial belts in Caloocan and Quezon City, and the constant flow of vehicular traffic throughout Metro Manila, are primary drivers of its air pollution profile. The dense urban fabric limits natural ventilation, further hindering pollutant dispersal and contributing to localized air quality degradation.

San Juan’s tropical climate dictates a wet and dry season pattern, significantly influencing its air quality. The dry season, typically from November to May, presents the greatest air quality concerns. Reduced rainfall and lower humidity during these months lead to increased photochemical smog formation. Solar radiation, intense throughout the year, drives reactions between nitrogen oxides (NOx) and volatile organic compounds (VOCs) emitted from vehicles and industrial sources, resulting in elevated ground-level ozone. Temperature inversions, common during the cooler months (December-February), trap pollutants near the ground, exacerbating the problem. The monsoon season (June-October) brings increased rainfall, which naturally helps to cleanse the air by washing away particulate matter. However, heavy rainfall can also lead to flooding, which can temporarily release pollutants from inundated areas. Wind patterns are generally variable, but during the dry season, weaker winds can contribute to pollutant stagnation. March and April often experience the poorest air quality due to a combination of high temperatures, intense sunlight, and relatively calm winds. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should limit prolonged outdoor activity during these months. During the wet season, while overall air quality tends to improve, periods of heavy fog can still trap pollutants, so caution is advised. Maintaining vehicle maintenance and reducing unnecessary travel are crucial year-round, but particularly important during the dry season.