Why Did Sulphur Dioxide Double During Lockdown?

While air quality across Britain generally showed a marked improvement during lockdown, one particular pollutant displayed an astonishing increase in its concentrations. A new study conducted by the University of Liverpool has demonstrated that sulphur dioxide (SO2) levels actually doubled during the first 100 days that quarantine measures were in place.

While the researchers behind the report are not entirely sure why such a phenomenon occurred, it has been posited that a drop-off in other contaminants may have interfered with the delicate balance of air chemistry. This, exacerbated by a summer of hot weather and low humidity, may have served to enhance the prominence of SO2 in the environment.

Double the trouble

SO2 is a harmful gas which can damage the human body, the natural world and the environment. People who are exposed to SO2 over even a short period can experience breathing difficulties, especially if they already suffer from underlying conditions such as asthma. Children are particularly vulnerable.

However, it’s when SO2 is allowed to build up in the atmosphere that it can really become dangerous, since it can mutate into other sulphur oxides (SOx), which are a chief component of particulate matter (PM). PM are particles of pollution that are considerably finer than a human hair, meaning they can be easily inhaled into the lungs and can even infiltrate the bloodstream. This can have devastating effects on the cardiovascular and respiratory systems of those exposed to them.

The biggest cause of SO2 emissions is normally fossil fuel power stations and other industrial plants, while the shipping industry is another chief contributor (even though the sector is moving towards improving maritime air quality), as well as other natural sources like volcanoes.

Causes unknown

It would have been expected, then, that SO2 levels would have fallen during the height of COVID-19 mitigation measures in line with other pollutants, but the reverse turned out to be the case. SO2 concentrations were up by over 100% in many parts of the country. The cause of the sharp increase in this particular contaminant is not fully understood, although those behind the research have their own theories.

“We think these changes could be driven by an imbalance in the complex air chemistry near to the surface exacerbated by the meteorological conditions in particularly low humidity levels and changes in pollutions concentrations,” explained Dr Jonny Higham, lead author on the study.

“It is important to note that the complex and relatively stable air composition in the near surface layer can be disrupted in a short period of time by the significant reduction of primary emissions from human activities. For the case of UK, getting cleaner air from a large NO2 reduction may not be as straightforward as it seems."