Volcanic smog or vog was observed in the Taal Volcano area on Monday, Phivolcs said as it advised residents in the area to wear N95 or medical-grade face masks.
Vog contains volcanic gas such as sulfur dioxide, which can irritate the eyes, throat, and respiratory tract, it said. Over the weekend, high levels of volcanic sulfur dioxide and steam plumes rising as high as three kilometers were observed from the Taal main crater.
The vog brought haze over the caldera region, Phivolcs said. Taal remains at Alert Level Two, indicating increased unrest.
The elderly, pregnant women, children, and those who have asthma or other health conditions are told to avoid outdoor activities, stay indoors and keep the windows and doors closed to block out the vog.
Aside from wearing N95 masks, residents should drink plenty of water to reduce throat irritation.