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Marilao is strategically positioned within Bulacan province in Central Luzon, Philippines, approximately 25 kilometers north of Metro Manila, placing it within the rapidly urbanizing periphery of the National Capital Region. The city sits on the vast Central Luzon Plain, characterized by flat to gently rolling terrain with an average elevation of just 10 meters above sea level, which significantly influences its air quality dynamics. Marilao is traversed by the Marilao River, part of the larger Marilao-Meycauayan-Obando River System that flows into Manila Bay, though this waterway has faced pollution challenges. The city's location within the industrial corridor extending north from Metro Manila means it hosts manufacturing zones, particularly along major highways like the North Luzon Expressway, contributing to urban and industrial emissions. Surrounding areas feature a mix of agricultural lands—primarily rice paddies and fishponds—and expanding residential developments, creating an urban-rural gradient where pollution sources from traffic, factories, and occasional agricultural burning interact. Proximity to the Sierra Madre mountain range to the east provides some topographic influence, but the low-lying plains allow pollutants to accumulate, especially during periods of stagnant air. This geographic setting, combined with its role as a transportation hub connecting northern provinces to Manila, makes Marilao susceptible to regional air quality issues exacerbated by local urban growth and industrial activity.

Marilao experiences a tropical monsoon climate with distinct wet and dry seasons that shape its air quality patterns throughout the year. During the dry season from November to April, particularly from January to March, pollution levels typically peak due to reduced rainfall, increased industrial and vehicular activity, and occasional temperature inversions that trap pollutants near the ground. The cool, dry months of December to February may see higher particulate matter concentrations from road dust and construction, making outdoor activities less favorable, especially for sensitive groups like children and those with respiratory conditions. The wet season from May to October brings relief through frequent monsoon rains that wash pollutants from the air, with June to August often showing improved air quality despite higher humidity. However, occasional typhoons from July to October can stir up debris and cause temporary spikes in particulate matter. Wind patterns, influenced by the northeast monsoon (Amihan) from November to March and the southwest monsoon (Habagat) from June to September, help disperse pollutants, though calm periods during transitions can lead to accumulation. For health guidance, sensitive individuals should monitor air quality reports and limit outdoor exertion during peak dry months, while the rainy season offers better conditions for outdoor activities, though attention to weather hazards like storms is advised.