What Volcanic Ash Carries in the Air

Eruptions at Anak Krakatau, Ile Lewotolok, Semeru, and several other active volcanoes have dominated national coverage these past few weeks. Ash-choked skies, dust-covered streets, and rooftops buried under volcanic material have become the most visible face of the activity.

Anak Krakatau is one case in point, still showing heightened activity as of Friday (11/9/2026). The Geological Agency recorded seven low-frequency earthquakes, four hybrid or multiphase earthquakes, four shallow volcanic earthquakes, four deep volcanic earthquakes, and one continuous tremor.

The head of the Geological Agency, Lana Saria, said Anak Krakatau remains at Alert status (Level III). The public and tourists are advised to stay outside a 3-kilometer radius of the center of activity.

With volcanic activity running high across Indonesia, public attention tends to fix on ashfall. But an eruption also carries other particles that can't be seen, said Arini Fadhilah, S.Farm., M.Si., a toxicology lecturer at the Faculty of Pharmacy, Universitas Muhammadiyah Surakarta (UMS).

An eruption produces several kinds of exposure, Arini explained, each working through a different mechanism. Alongside volcanic ash there are volcanic gases such as sulfur dioxide (SO2), carbon dioxide (CO2), hydrogen chloride (HCl), carbon monoxide (CO), and hydrogen fluoride (HF), each with its own characteristics and health risks, and each calling for its own kind of personal protection.

"What people need to understand is that an eruption doesn't only produce ash. There are volcanic particles, volcanic gases, and secondary hazards that show up after the eruption," Arini said in an online interview on Friday (11/9/2026).

For all the anxiety that flares up each time a volcano erupts, the most important step, Arini believed, is reducing exposure. The basic rule is to stay indoors when ash is falling.

Doors and windows should be shut tight to keep particles out. Fans and air conditioners that pull in outside air should be switched off for the time being.

"If people have to go out, we recommend a particulate respirator, an N95, KN95, KF94, or FFP2, fitted properly so it seals around the nose and mouth," Arini said.

A mask's effectiveness, she said, depends not just on the type but on how well it fits the wearer's face. A loose mask still lets particles slip in through the gaps along the sides.

Eye protection matters too, since ash is abrasive. Protective glasses or goggles help keep particles from reaching the eyes directly.

The skin should be covered as well, with long sleeves, long trousers, and closed shoes to limit contact with the ash.

Amid all this guidance, though, social media has filled with complaints about a jump in the price of health supplies, especially masks.

Citing Kompas, mask prices climbed sharply as volcanic ash spread after Anak Krakatau's eruption from Sunday (6/9/2026) into Monday (7/9/2026).

"The people selling masks are just awful. Last night I checked out, then this morning it got canceled, they said the price went up. When I saw the new price, it had literally gone up tenfold. I hope the ash at your house just keeps swirling around forever! ????!!!!!" wrote @bapethh, as quoted by Kompas on Friday (11/9/2026). The post had received 1,900 reposts and 32,800 comments.

This, Arini said, showed how many people still misunderstand what masks actually do during an eruption. A fair number assume a KN95 can protect against every hazard a volcano throws off.

"N95 and KN95 masks are particulate respirators, built to filter particles like volcanic ash, not gases. So they don't offer adequate protection against SO2," she explained.

Dealing with gas exposure calls for a specialized respirator, one fitted with a cartridge or canister made to absorb acidic gases. Even that can't be used casually, since how well it works depends on the type of cartridge, the gas concentration, how long you're exposed, and how properly the respirator is fitted.

Panic buying, then, is not the answer. The presence of SO2 doesn't mean everyone suddenly needs a gas mask. If the main threat is ash, a properly worn particulate respirator is enough, while protection against gas should be matched to what air-quality monitoring actually shows.

"Rather than panic, people just need to limit their exposure and follow official information on air quality and evacuation," she said, driving the point home.

Arini said that although it may look like ordinary dust, volcanic ash is actually eruption material with abrasive properties, meaning it can scratch easily. Its particles are also extremely fine, so they can enter the respiratory tract when inhaled.

The smaller the particle size, the more easily it can reach the lungs. As a result, people can experience coughing, a stinging sensation in the throat, nasal irritation, and worsening of pre-existing asthma or lung conditions.

Volcanic ash can also irritate the eyes. The surface of the eye can become abraded by friction from the fine particles, causing stinging, redness, and watering.

On top of that, some volcanic ash can contain crystalline silica. This compound is known to be linked to silicosis when someone experiences repeated exposure over a long period of time.

"But people shouldn't immediately jump to the conclusion that being caught in an ashfall once will definitely lead to that disease," Arini said, cautioning against overreaction. According to her, the risk of silicosis is more closely tied to ongoing respirable exposure, not a single eruption event.

Besides volcanic ash, rumors about the spread of SO2 following the Anak Krakatau eruption have also been widely discussed. This gas is indeed often associated with a sharp smell resembling sulfur or a freshly struck match.

SO2 is a colorless gas, so it can't be identified by sight alone, unlike volcanic ash, which is clearly visible.

"Volcanic ash and SO2 can both irritate the eyes and respiratory tract, even though the form of exposure is different," she explained.

At low concentrations, SO2 exposure can cause stinging eyes, irritation of the nose and throat, and coughing. But as concentration increases, the impact can become far more serious.

According to Arini, SO2 gas can trigger bronchoconstriction, or narrowing of the airways. People with asthma are among the groups most vulnerable to a worsening of their condition.

At very high concentrations, SO2 exposure can even cause severe respiratory distress and oxygen deficiency. Even so, the public also doesn't need to panic immediately every time they hear the term sulfur dioxide.

According to her, the presence of volcanic gases such as SO2 is simply a natural characteristic of volcanic activity. But the level of danger depends on gas concentration, wind direction, duration of exposure, and a person's location relative to the source of the eruption.

"In real world conditions, people are almost never exposed to just one substance," Arini said.

Volcanic ash and volcanic gas can appear at the same time. In fact, in the atmosphere the two can interact with other pollutants, forming an even more complex mixture.

Arini explained that one possibility that can arise is an additive effect. Volcanic ash and SO2 both irritate the respiratory system, so when the two are present together, the resulting discomfort can be more severe than exposure to either one alone.

"Research from various countries that I've studied also shows that the surface of volcanic ash can become a place where various pollutant compounds from the atmosphere attach themselves," she explained.

However, she cautioned that people shouldn't immediately link those research findings to every eruption event.

"Findings from one region don't mean the ash from every volcano will necessarily contain hazardous compounds at the same levels," she said.

SO2 itself, she continued, can also undergo chemical changes in the atmosphere, forming extremely small sulfate particles, including PM2.5, which is known to easily enter the lungs.

Because of this, the health risk from an eruption isn't shaped by a single substance, but by a combination of various environmental factors.

Writer: Genis Dwi Gustati

Translator: Farizal Luqman Majid

Editor: Al Habiib Josy Asheva