BOCAUE, Bulacan — Several local government units in Bulacan have suspended school classes in the afternoon on Friday (September 22) as smog from Taal Volcano spread in Bulacan.

Among the LGUs that suspend afternoon school classes were Bocaue, Marilao and Santa Maria upon the recommendation of its local disaster risk reduction management offices.

An advisory from the Department of Science and Technology on Friday morning said “The meteorological conditions this morning (NCR, CALABARZON, and some parts of Central Luzon) is condusive for haze or smog formation. This occurs when very small particles get trapped close to the surface due to the presence of a thermal inversion, high humidity, and calm wind conditions. These floating minute particles in the air could be from smoke, pollutants, or volcanic aerosols.

Thermal inversion occurs when layers of the atmosphere don’t mix causing aerosols to get trapped.

Usually, the inversion disappears later in the day as heat from the sun allows the mixing of the air, allowing the aerosols to disperse. However, cloudy conditions may reduce surface heating, allowing the haze to persist.