With over 1500 active volcanos worldwide, gases and ash emitted from volcanic eruptions is an international issue. Volcanic smoke, also known as “vog”, can travel hundreds, and even thousands of miles away from a volcano and affect distant communities. So what exactly do volcanos emit? How do volcanos affect air quality?
Gases Emitted By Volcanos
Volcanos emit a variety of gases including H20, CO2, SO2, H2, CO, H2S, and HCL. The most abundant gas is typically water vapor (H20).
Below shows the percentage concentration of gases released by three volcanos. Note the large difference between each volcano’s emissions. It is typical for the types of gases and their proportions to vary widely between volcanos.
| Volcano | Kilauea Summit | Erta’ Ale | Momotombo |
| H20 | 37.1 | 77.2 | 97.1 |
| CO2 | 48.9 | 11.3 | 1.44 |
| SO2 | 11.80 | 8.34 | 0.50 |
| H2 | 0.49 | 1.39 | 0.70 |
| CO | 1.51 | 0.44 | 0.01 |
| H2S | 0.04 | 0.68 | 0.23 |
| HCL | 0.08 | 0.42 | 2.89 |
Outside of water vapor, volcanos also emit a large amount of CO2, around 200 million tons per year. But contrary to a popular myth, volcanos do not produce even close to the amount of CO2 produced by human activities. Studies show human activity is responsible for over 130 times the amount of CO2 emitted by volcanos.
Furthermore, volcanos also makeup the world’s largest sources of SO2, HCl, and HF emissions.
Particulates Emitted By Volcanos
Volcanos also emit rock, mineral, and glass particles into the air, called tephra. The largest pieces of tephra (>64mm) typically fall to the ground close to the volcano.
Ash particles on the other hand (particles <2mm) can reach high levels in the atmosphere and travel hundreds and even thousands of miles. These particulates can be as small as .001 mm or 1 micron. Particulates this small, called PM2.5, are particularly dangerous to humans as they are small enough to enter the bloodstream and organs.
Read More: Do Air Purifiers Remove PM2.5?
Most of the tephra larger than 1mm fall to the ground within 30 minutes of eruption. But particles less then .01 mm can stay in the atmosphere for two or three years!
Volcanic ash samples show volcanos emit much more larger, coarser particulates than finer particulates. But these collections may undercount the amount of smaller particulates emitted, as they are more likely to stay suspended in the air. Below is a distribution of particle size from Eyjafjallajökull volcano in Iceland.
How Do Volcanos Affect Air Quality?
How volcanos affect air quality can vary greatly between volcano. Factors such as size and power of the eruption, as well as local wind conditions can play a large role in how air quality is affected. But volcanos have the ability to disrupt air quality in the following ways:
Volcanos Can Raise Dangerous PM2.5 and PM10 Levels
Dangerous fine particulate levels can rise significantly nearby a volcano eruption largely due to volcanic ash. Data shows volcano eruptions can increase levels in PM2.5 particulates, as well as larger PM10 particulates. These particulates are a serious danger to our health and the environment.
WATCH: 5 Things You Should Know about PM2.5 Air Pollution
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Studies show volcanos affect PM10 levels even more than PM2.5 levels close to the eruption. The reason is that volcanic ash typically contains a lower ratio (.23) of PM2.5 to PM10 than what is present in typical urban air pollution (.65). That being said, it is generally the smaller PM2.5 sized volcanic ash that can travel great distances, affecting communities far from the eruption.
How far can these particulates travel? Data shows volcanic vog particulates can travel thousands of miles around the world.
Some examples of increased PM2.5 and PM10 levels due to volcano eruptions:
*The 1980 Mount St. Helens eruption in the US led to elevated concentrations of PM10 for months, ranging from 50–570 μg/m3, many times over the WHO recommended limit.
*The Eyjafjallajökull volcano eruption in Iceland during 2010 increased PM10 concentrations to over 50 μg/m3 on 25 days during that year.
*PM2.5 levels were recorded over 165 μg/m3 at the rim of Masaya Volcano in Nicaragua, over 16 times the WHO recommended annual limit.
Sulfur Dioxide (SO2) Can Reach Dangerous Levels Close to Eruption
In the absence of strong winds, SO2 emitted by Kilauea can accumulate in the air and reach levels that exceed federal health standards. In Hawai`i Volcanoes National Park, this has occurred more than 85 times since 1986. SO2 is very toxic and in high concentrations can be deadly.
Sulfur Oxides Emitted By Volcanos Can React With Sunlight To Create PM2.5
Sulfur oxides can also contribute to the creation of fine particulate matter such as PM2.5 far from the eruption. How does this happen? Chemistry! SO2 released from the volcano can react with sunlight, atmospheric gases and aerosols, and convert to fine particles.
The farther volcanic vog travels from the volcano, the more PM2.5 and harmful particulate matter the vog contains. Why? The more time SO2 is suspended in the air, the greater the chance it will react to create PM2.5.
In fact, a study shows 90% of SO2 from a volcano eruption is converted to fine particulate matter within one month.
Volcanos Create Acid Rain
Toxic gases emitted from volcanos, in particular SO2, HCl, and HF, mix with water vapor to form acid rain, which can harm crops downwind from the eruption.
The eruption of the Turrialba volcano in Costa Rica in 2014 created a great deal of acid rain, which in turn had a major impact on the surrounding area’s agricultural industry. It is estimated that the acid rain impacted up to 65 hectares of crops in the area.
Read More: How Volcanos Can Be a Danger to Your Health
Bottom Line: How Do Volcanos Affect Air Quality?
Volcanos can create dangerous levels of SO2 close to the eruption, as well as PM2.5 and PM10. Further away from the eruption, volcanic gases can react and create PM2.5, which can spread for thousands of miles.
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