There is little doubt that humans pollute the air by operating power plants, factories, and large-scale farms. Transportation, be it by automobile, ship, or airplane contributes a significant amount of air pollution as well. According to a press release from Eurekalert, however, these are not the only sources of toxic gas that you need to be worried about.

A massive eruption from a volcano called Bárðarbunga in Iceleand was found to release as much as three times the amount of toxic gas that is currently emitted by all of the industry in the entire continent of Europe, based on a new study.

The volcano released at least 120,000 tons of sulphur dioxide gas per day, which is the leading cause behind acid rain and can also lead to serious respiratory issues. The eruption, which happened last year, is the biggest on record in the last 200 years. A river of lava flowed throughout the northern section of Iceland for a duration of nearly six months.

A team of European scientists from the universities of Leeds and Edinburg, in addition to researchers from the Met Office, used satellite imaging data to map where the sulphur dioxide was going, and how much there was being emitted from the volcanic eruption. They created computer models that predicted where the gas was likely to end up.

Sulphur dioxide doesn’t just come from volcanoes. It is also produced by the burning of fossil fuels and as a byproduct of certain industrial processes, like smelting. Although levels of manmade sulfur dioxide in the atmosphere have been on a steady decline for the past two and a half decades, the contribute from Bárðarbunga volcano in 2010 put a significant amount of the gas into the atmosphere.

The study was published in the Journal of Geophysical Research, and was supported by the Natural Environment Research Council and the Royal Society of Edinburgh, among other supporters. According to one of the researchers that worked on the study, Dr. John Stevenson of the University of Edinburgh’s school of GeoSciences, “This eruption produced lava instead of ash, so it didn’t impact on flights – but it did affect air quality. These results help scientists predict where pollution from future eruptions will spread.”

Dr. Anja Schmidt, from the School of Earth and Environment at the University of Leeds, who was also the study’s lead author, explains further: “The eruption discharged lava at a rate of more than 200 cubic meters per second, which is equivalent to filling five Olympic-sized pools in a minute. Six months later, when the eruption ended, it had produced enough lava to cover an area the size of Manhattan.”

The sulfur dioxide pollution from the eruption tapered off over time, but when it began it was eight times higher than the levels produced by all man-made sources in Europe each day.

According to the EPA, sulfur dioxide is one of a group of extremely reactive gasses referred to as “oxides of sulfur.” Behind volcanoes, the largest man-made source of these gases is from the combustion of fossil fuels at power plants and other industrial facilities. Smaller SO2 sources include smelting, or extracting metal from ores, and the burning of fuels for large transportation vehicles like trains, ships, and non-road equipment, which contains high levels of sulfur.

Sulfur pollution used to be a serious problem, but authorities have taken steps to mitigate its negative impacts on the environment. The EPA first set standards for the gas in 1971, with levels not to exceed 140 ppb daily and a 30 ppb annual average standard. It set the cap for short-term emissions, over a three-hour period, at 500 ppb. It revisited the regulations again in 2010 and established a new 1-hour standard at a level of 75 parts per billion, and revoked two primary standards that were in place from the original regulation because they did not provide any additional benefit after the new standards were put in place.

One of the biggest risks posed by sulfur dioxide is acid rain. SO2 is one of the main precursors for this phenomenon, along with nitrogen oxides. Both of these chemicals come from the power sector. The EPA put forth the first cap and trade program in the nation, and allowed polluters to trade credits to reduce the overall level of pollution with a market-based system.