Aerosol optical depth in NCR back to normal after ashfall —findings

The aerosol optical depth (AOD) has returned to normal levels in Metro Manila following the ashfall caused by the eruption of Taal Volcano in Batangas, according to the Manila Observatory on Tuesday.

A report by the Manila Observatory said AOD is "the measure of how much sunlight is prevented from reaching the ground due to aerosols." It said the "higher the AOD means the conditions are hazier."

"[B]efore the ashfall, [AOD] was around 0.36, which is somewhat polluted but typical for Metro Manila. Over a four-hour period during the peak of the ashfall in Quezon City, AOD reached over four times that value, signifying extremely hazy conditions," the report read.

"More recent measurements show that AOD values have returned to normal over the Manila Observatory. Based on the latest satellite images, emissions from the volcano have decreased and prevailing winds are advecting residual emissions in the northeast direction," it added.

From usual levels of 0.36 before the ashfall, the AOD peaked at ~1.66 over the Manila Observatory, before decreasing to ~0.34 on Sunday, according to the report.

Taal Volcano on Sunday spewed ashes in a phreatic eruption due to hydro-thermal activities. According to the National Disaster Risk Reduction and Management Council, more than 5,000 families or over 20,000 residents in Batangas and Cavite were affected.

Alert Level 4 was still raised over Taal Volcano as of Tuesday, meaning hazardous eruption is highly possible. —KBK, GMA News