Manila: The Department of Environment and Natural Resources (DENR) reported that hazy skies observed in the National Capital Region (NCR) on Monday were likely due to two separate fire incidents in Quezon City and the neighboring Rizal province.

According to Philippines News Agency, the fires occurred at a sanitary landfill in Montalban town and a warehouse along Commonwealth Avenue in Quezon City, as stated by the agency's Environmental Management Bureau (EMB). Real-time air quality monitoring by the DENR-EMB indicated that concentrations of particulate matter, specifically PM10 and PM2.5, reached their peak between 5 a.m. and 7 a.m.

However, by around 9 a.m., the EMB reported that readings had normalized and returned within the guideline values. Particulate matter, or PM, is a mixture of solid particles and liquid droplets in the air. PM10 are inhalable particles with diameters generally 10 micrometers and smaller, while PM2.5 are fine inhalable particles with diameters 2.5 micrometers and smaller, which can pose health risks, particularly for sensitive groups such as children, the elderly, and individuals with pre-existing respiratory conditions.

"The air quality reading varies in time and place and can change at any time depending on pollution sources and meteorological factors. DENR-EMB will continue to monitor air quality," the agency stated. It reassured the public of ongoing air quality monitoring and emphasized the importance of remaining cautious during pollution events like fires.

Previously, the Quezon City government issued a warning and advised residents to wear face masks following an Air Quality Index (AQI) reading of "unhealthy" and "very unhealthy" levels in certain areas. The city government highlighted that unhealthy air quality could pose health risks, especially to individuals with respiratory illnesses.