It's smog, not vog.
According to the Philippine Institute of Volcanology and Seismology (PHIVOLCS), the gray skies in Metro Manila are not related to the vog observed in Taal.
On Friday, several local government units in Metro Manila and Calabarzon suspended classes at all levels in public and private schools due to warnings and advisories about volcanic smog or vog over Taal Volcano.
However, PHIVOLCS and the Department of Energy and Natural Resources - Environmental Management Bureau (DENR-EMB) clarified that the gray haze blanketing the region is "primarily attributed to emissions from heavy vehicular traffic, especially during rush hour."
It also said that it was not possible for the vog to reach Metro Manila as the surface winds were “coming from the northeast direction going to the southwest direction, or going away from Metro Manila.”
The bureau also added that the air quality "varies in time and place and can change anytime depending on pollution sources and meteorological factors.”
“Normally, air temperature decreases with increasing altitude, but during an inversion warmer air is held below the cooler air. An inversion can also suppress convection which is the ability of pollutant to move vertically causing visibly trapped particulate matter closer to the ground,” the agency explained.
Because of this, LGUs in Metro Manila have issued a health advisory urging residents to stay indoors and wear face masks when going out.
The elderly, pregnant women, children, and those with respiratory problems and heart problems are especially at risk.
Last Sept. 21, PHIVOLCS reported that the Taal Volcano released 4,600 tons per day of sulfur dioxide, causing high levels of vog in nearby areas. They noted however that the current alert level 1 is not considered to be a major threat.