Acid rain in Cebu possible after Kanlaon eruption

CEBU CITY, Philippines — Air quality in parts of Cebu has remained within the “good” range following the eruption of Mt Kanlaon on Thursday, July 9. But environmental authorities are warning residents not to let their guard down as volcanic gases carried by prevailing winds could still lead to acid rain.

In an advisory issued Friday afternoon, July 10, the Department of Environment and Natural Resources–Environmental Management Bureau in Central Visayas (DENR-EMB-7) said continuous air quality monitoring showed particulate matter levels remained within the “good” category.

However, the agency said south-southwest winds continue to carry sulfur dioxide (SO₂) and other volcanic gases across the region. With the ongoing rainy weather, these gases may combine with atmospheric moisture and form acid rain.

READ: Kanlaon ashfall, sulfuric smell reported in some NegOcc areas

Air quality remains ‘Good’

Based on telemetry data as of 3 p.m. Friday, the Continuous Ambient Air Quality Monitoring Station (CAAQMS) in Talisay City recorded PM2.5 at 18.2 micrograms per cubic meter, equivalent to an Air Quality Index (AQI) of 36, while PM10 reached 27.0 micrograms per cubic meter with an AQI of 25. Both readings were classified as “good.”

Meanwhile, the CAAQMS at Therma Visayas Inc. (TVI) in Toledo City recorded PM2.5 at 4.4 micrograms per cubic meter, equivalent to an AQI of 9, while PM10 measured 13.0 micrograms per cubic meter with an AQI of 12, which also falls under the “good” category.

Despite these readings, the EMB emphasized that good AQI readings do not mean residents are no longer at risk from volcanic gases being carried across the region.

READ: Kanlaon ashfall strikes 2 with respiratory illness in Cebu

Why acid rain remains a concern

According to the EMB, south-southwest winds continue carrying sulfur dioxide and other volcanic gases released by Kanlaon Volcano across Central Visayas.

The agency said these gases, combined with atmospheric moisture amid rainy weather may form acid rain.

Acid rain, the EMB said, may cause mild skin irritation, damage backyard crops and other vegetation, and gradually corrode exposed metal surfaces such as roofs, vehicles, and outdoor equipment.

What residents should do

While monitoring continues, the EMB urged residents to continue taking precautions even if current air quality readings remain within safe levels.

Residents are advised to stay indoors during rainfall and avoid unnecessary outdoor exposure. Those who get caught in the rain should immediately take a bath and thoroughly rinse their skin and hair with clean water.

Households are also encouraged to keep rain barrels, open water containers, and deep wells securely covered to prevent volcanic contamination.

To reduce exposure to any remaining volcanic ash, residents should keep doors and windows closed whenever possible.

Those who need to go outside are advised to wear properly fitted N95 or KN95 face masks together with protective eyewear.

The EMB also encouraged residents to protect plants and property by placing sensitive potted plants under shelter when possible or gently rinsing their leaves with clean water after rainfall.

Ash deposits on rooftops should likewise be safely washed away before they harden.

Monitoring continues

As of Friday afternoon, Pagasa recorded an ambient temperature of 28.1 degrees Celsius, with south-southwest winds blowing at 7 meters per second.

The EMB said it will continue monitoring ambient air quality and advised residents to stay informed by monitoring official government advisories for further updates.

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