Polluters can no longer hide their emissions of sulphur dioxide by failing to report them. Canadian researchers have found a way to detect that kind of pollution using satellites.

In doing so, they've uncovered some very big polluters: oil and gas plants in the Persian Gulf that hadn't been reporting their emissions.

Those polluters may be responsible for six to 12 per cent of man-made emissions worldwide of sulphur dioxide, reports the new study led by Chris McLinden, a research scientist at Environment and Climate Change Canada. The results were published this week in the journal Nature Geoscience.

McLinden and his colleagues used data from NASA's Earth-observing AURA satellite, launched in 2002, which carries an instrument capable of measuring sulphur dioxide. (NASA)

The data also confirmed reports that sulphur dioxide emissions are falling worldwide.

Sulphur dioxide is a pollutant that can generate acid rain, which is harmful to many freshwater animals. And it produces particulate matter that's harmful to human health when we breathe it in.

It's been linked to both short-term risks such as asthma, as well as potentially deadly long-term risks such as lung cancer and cardiovascular disease.

"Globally, that's the component of air pollution for which the most deaths are attributed," McLinden said.

Because of that, sulphur dioxide-producing facilities mainly coal-fired power plants, the oil and gas industry and ore — smelters — are required to report their emissions to federal agencies such as Environment and Climate Change Canada each year.

Those are combined into international inventories that track worldwide emissions so scientists can use them to calculate potential effects, such as rates of premature mortality in a particular region that can be linked to measured levels of particulate matter.

Inaccurate statistics

In Canada, industrial facilities typically measure sulphur dioxide emissions directly using a device that's attached to smokestacks, generating fairly accurate readings. But in other countries, the statistics may be based on estimates, McLinden said.

This map shows man-made sources of sulphur dioxide pollution detected by satellite that haven't been reported in global inventories. Many of the biggest sources are in the Persian Gulf and Mexico. (Chris McLinden/Environment and Climate Change Canada)

Sometimes, measurements don't jibe with known local sources, he added. Things like that lead scientists to suspect that there are sources missing from conventional international inventories of pollutants.

"There's so many sources, I think people just assume that a few are falling through the cracks, especially maybe in developing nations that don't have the same rigorous reporting obligations," he added.

Scientists have been discussing the possibility of being able to track pollutants using satellites in space for a long time, but the study authors think this is the first time they've actually succeeded.

McLinden and his colleagues used data from NASA's Earth-observing AURA satellite, launched in 2002, which carries an instrument capable of measuring sulphur dioxide. The data was combined with information about wind directions and wind speeds to pinpoint sulphur dioxide sources.

Volcano surprise

"Initially, I think we maybe thought it wasn't working when we got these huge sources in the middle of the Pacific," McLinden recalled.

Those turned out to be volcanoes — the study found 75 of them emitting substantial amounts of sulphur dioxide, despite the fact that they were dormant and not erupting.

A general view shows a unit of South Pars Gas field in Asalouyeh Seaport, north of Persian Gulf, Iran November 19, 2015. The new study suggests that oil and gas plants in the Persian that haven't been reporting their sulphur dioxide emissions may be responsible for six to 12 per cent of man-made sulphur dioxide emissions worldwide. (Raheb Homavandi/Reuters)

"Most of them hadn't been measured before," McLinden said. The study found that the dormant volcanoes were emitting almost 30 per cent of the sulphur dioxide in the atmosphere (with the rest being man-made), although erupting volcanoes might emit much more.

The researchers compared the sources identified by the satellite data with global sulphur dioxide inventories.

They found that many smaller sources couldn't be detected by satellite.

"On the other hand, we noticed that conventional inventories were missing some fairly sizeable SO2 [sulphur dioxide] sources," McLinden said.

In some regions, the inventories were off by a factor of three or more compared to the measurements.

The densest cluster of unreported emitters was in the Middle East. Further research identified where they were coming from — mostly oil and gas extraction facilities.

"Google Earth was a huge help," McLinden said.

Other previously unknown sources included oil and gas facilities and a power plant in Mexico, along with other industrial sources in Africa and Asia.

No missing sources in Canada

"As a Canadian, it was certainly reassuring to see there was none of these missing sources in Canada," McLinden added.

The new study was led by Chris McLinden, a research scientist at Environment and Climate Change Canada. (Courtesy Chris McLinden)

Overall, the more complete data will help scientists generate more accurate pollution forecasts and estimates for things like premature mortality from pollution, McLinden said.

"Ultimately what this will lead to, we hope, is better global inventories that can be used to make better decisions," he added.

In theory, the information could also be used to help enforce environmental regulations, but that depends on the laws and policies of individual countries, McLinden said.

The researchers think the new technique could be used to detect some other pollutants from space, such as nitrogen oxides.

Some pollutants, such as carbon dioxide and methane, may be more challenging to measure using satellites because their sources are more densely clustered and they stay in the atmosphere for a much longer time.

The study included scientists from Dalhousie University in Halifax, NASA Goddard Space Flight Center, University of Maryland, and the Harvard Smithsonian Center for Astrophysics.