Beginning on the morning of 21 December 2020, Mt. Kilauea in Hawaii, USA and Mt. Etna in Sicily, Italy, two of the world’s most active volcanoes, were erupting explosive plumes of lava and ash at the same time in a seeming geological coincidence. This has resulted in a large-scale air quality impact for thousands of miles beyond the eruptions themselves.

Around 9:30 PM local time on 20 December 2020, Mt. Kilauea began to erupt and spew ash into the air for hundreds of miles around the U.S. state of Hawaii and caused a 4.4-magnitude earthquake. Authorities on the island urged residents of the island to stay inside to avoid the toxic impact of ash blown from the eruption into the surrounding regions.¹

In the hours following the 20 December eruption, the air quality index (AQI) in communities like Pahala, Naalehu, and Ocean View appeared to rise gradually following the initial eruption, with the Kahuku Cross Fence station on the Ko’olau Summit Trail recording AQI measurements well into the 100s (“unhealthy for sensitive groups”) by the middle of the day.

Pictured: Air quality monitoring stations around the southern tip of the big island of Hawaii southwest of Mt. Kilauea (represented by the fire icon in the top right of the image), with AQI measurements over 100 (“unhealthy for sensitive groups”) near the Kahuku Cross Fence station on the Ko’olau Summit Trail and well into the “moderate” range near Pahala.

The air quality impact of Kilauea may not seem immense at first glance. But over time, Kilauea’s eruptions have been linked to dangerously high levels of PM2.5(particulate matter with a diameter size of 2.5 microns or smaller)– in a 2020 study, researchers found that PM2.5 levels rose as high as 300 micrograms per cubic meter (μg/m3) (350 AQI) during a previous eruption in 2018, and this eruption is expected to have similar results.²

Mt. Etna, on the other hand, has already been erupting for over a week (since 14 December 2020) leading up to the Kilauea eruption. But on the morning of 21 December, volcanologists recorded Mt. Etna as showing “strong explosive activity,” with huge amounts of ash and lava bursting out of the volcano during violent periods called “paroxysms.”³

Pictured: Increasing poor air quality recorded across Sicily (indicated by the yellow haze covering much of the northern part of the island) on 21 December 2020 – relative location of Mt. Etna circled in red.

Hazardous air quality from Mt. Etna eruption

Throughout the previous week, Mt. Etna had already emitted enormous clouds of volcanic ash as high as 15,000 feet (4600 meters, or 2.8 miles) into the air around the southern tip of Italy and beyond. Previous research has found that air pollution from Mt. Etna’s eruptions can rise as high 3.7 miles (6 kilometers) into the air.⁴

As renewed volcanic activity began on 21 December, the air quality impact became evident many miles away.

Late into the day on 21 December, dense clouds of steam and ash continued to rise high into the atmosphere. Wind currents have been blowing smoke from Mt. Etna as far away as southern and eastern Europe, where air quality has already been poor for weeks due to wood-burning in homes and cold weather trapping air pollution close to the ground level.

Pictured: Air quality impacts of Mt. Etna’s eruption throughout southern and eastern Europe (Sicily picture at bottom center of image). Sarajevo, Bosnia and Herzegovina recorded as the most polluted city in the world with an AQI of 465 – well into the “hazardous” range at which dangerous health effects are experienced by everyone.

With this trifecta of volcano smoke, wood-burning, and cold temperature, much of south and eastern Europe experienced AQI measurements well into the 100s and 200s.

Late on 21 December 2020, the city of Sarajevo reached number one on the World AQI Ranking, peaking at 465 and surpassing the cities of Kolkata and Delhi in India that had been experiencing hazardous air quality for months earlier.

Pictured: IQAir AirVisual World’s Most Polluted Cities ranking, with the city of Sarajevo in Bosnia and Herzegovina recorded as the world’s most polluted city.

Smoke from Mt. Etna also appeared to travel as far south as northern and western Africa. Wind currents blew smoke southwest from the Mediterranean sea surrounding Sicily deep into the African continent. Here, air pollution from vehicle and industrial emissions as well as biomass and wood burning for heat are also common.⁵

Pictured: Poor air quality in northern and western Africa resulting from a dangerous combination of vehicle and industrial emissions, biomass and wood burning, and volcano smoke from Mt. Etna.

The air quality index (AQI) helps illustrate the health risks of air quality measurements: the higher the levels of air pollution, the stronger the health impacts of air pollution on sensitive groups. When the AQI reaches 300 or higher, air pollution is considered to be at emergency levels – suggesting that the impact of Mt. Etna’s volcanic ash may have deadly consequences.

Pictured: U.S. AQI levels, PM2.5 levels, and health recommendations if a person is exposed to these levels of pollution for 24 hours.

Evolving air quality impact from Mt. Kilauea

At first glance, the air quality impact in Hawaii seemed less grim following the Kilauea eruption. Air quality data in the immediate environments surrounding the volcanos didn’t appear to show significant impacts from volcanic ash and smoke.

But Kilauea has regularly erupted and caused seismic activity like earthquakes and fissures in and around the volcano since 1983.⁶ And in the past, volcano smoke plumes from Kilauea have risen high into the air and traveled on wind currents for hundreds or thousands of miles as far southwest as Johnston Island – 1,000 miles southwest of Kilauea.⁷

This appears to be the case with Kilauea today – at a higher-level view, the air quality impact from smoke moving westward on trade winds can be seen from the Kilauea eruption out to sea. Continued monitoring may reveal that this ash has traveled much farther to the west along the global currents.

Pictured: Air quality data west of the Hawaiian islands. Note the wind currents moving westward and the growing areas of yellow (“moderate”) air quality recorded just west of the big island, indicating the possible impact of Kilauea (fire icon) on air quality many miles west.

Health impacts of volcano smoke

Volcano smoke and its associated pollutants can impact human health as far as thousands of miles from its source.⁸

Common volcanic smoke pollutants include:

• carbon dioxide
• sulfur dioxide
• carbon monoxide
• hydrogen sulfide
• carbon disulfide
• hydrogen chloride
• methane
• hydrogen fluoride
• hydrogen bromide
• heavy metals such as mercury, lead, and gold

Short-term health problems associated with volcanic smoke include:⁹

• skin and eye irritation
• bronchoconstriction
• respiratory disease aggravation

Long-term exposure to volcanic smoke can negatively impact respiratory, cardiovascular, and nervous systems.

Several volcanic gaseous pollutants can have serious to lethal impact on life. More than 1,700 people and 3,000 livestock died from a sudden release of carbon dioxide near the volcanic Lake Nyos, Cameroon in 1986.¹⁰

As noted in a 2020 study published in Medical Hypotheses, there is an association between air pollutants and severe viral respiratory disease.¹¹ The study has hypothesized that given the air pollutants contained in volcanic smoke including sulfuric acid, hydrogen sulfide, and hydrochloric acid, COVID-19 (a serious disease, often fatal, that is caused by the SARS-CoV-2 virus) may have been more easily diffused in Italy by Mount Etna’s pollutant contribution.

How to protect yourself from volcano smoke

To stay safe during a volcanic event, you should have a plan before, during, and after the eruption.^12,13,14,15

Your plan before a volcano becomes a threat should include advance supplies, knowing your community warning system, and having a shelter-in-place plan from ash. If your biggest risk isn’t ash, you may need to have an evacuation plan in place. Talk to your doctor if you have respiratory problems.

While a volcanic eruption is underway, you should protect yourself from smoke by taking the following steps:

• Avoid being downwind and in downstream valleys.
• Stay indoors unless you are in a hazard zone.
• Close and seal all doors, windows, ventilation, and chimney dampers.
• Place wet towels at the bottom of drafty doors.
• Use an air purifier for volcano smoke if volcanic pollutants seep indoors.
• Try not to use forced air heaters, air conditioners, or clothes dryers.
• Don’t operate fans.
• Make sure all animals are in closed shelters.
• Limit your time outdoors.
• If you must be outdoors, wear a well-fitting N95/KN95 air pollution mask(masks with a 95% efficiency rating – “N” designates a rating based on the U.S. standard, KN designates a rating based on the Chinese standard).
• If a mask is unavailable, use a handkerchief or cloth as a last resort.
• Don’t go on your roof to remove ash.
• Protect your eyes, skin, and cover your head.

After a volcanic eruption, you should continue to observe the following guidelines:

• Continue to avoid driving through heavy ash, which could clog machinery and stall your vehicle.
• If you have trouble breathing, stay indoors and avoid all contact with ash.
• Stay off the roof, as ash is very slippery.
• Use social media or text to contact loved ones. Phone lines may be down or overwhelmed.