Edinburgh, no stranger to an occasional haze, experienced an unprecedented atmospheric event on 31 May, unlike any seen over the past 30 years. While sea haar from the North Sea often blankets Scotland’s capital, the haze observed that Friday felt distinctively different. UKCEH researchers are currently investigating if this haze can be attributed to a volcanic plume that transited the UK following an eruption in Iceland.
A new fissure eruption occurred on the Reykjanes Peninsula in Iceland, the fifth eruption in a series that began in December 2023 near the town of Grindavik. Initially deemed a local concern due to its non-explosive nature, the eruption’s impact on UK’s air quality was thought to be minimal. However, meteorological circumstances caused sulphur dioxide (SO2) levels in Scotland to rocket to levels not witnessed since the 1970s on the morning of 31 May.
The Scottish Environment Protection Agency’s (SEPA) national volcanic emissions network first detected an increase in SO2 on the Isle of Lewis on the evening of 30 May. During the early hours, the plume moved southward, peaking in Scotland’s Central Belt by 6 am on 31 May. St Leonard’s in Edinburgh reported a maximum concentration of 1161 µg m-3.
Using a combination of observations and modelling data, UKCEH researchers were able to pinpoint the high SO2 levels, making it highly likely that the increased levels could be attributed to the Icelandic volcano. The UKCEH’s EMEP4UK atmospheric chemistry transport computer model application confirmed the sequence of events, indicating that if the eruption had occurred differently, the SO2 emissions might have missed the UK entirely.
What distinguished this from previous events is that significantly higher concentrations of SO2 were recorded than previously reported in the UK, surpassing those of previous Icelandic eruptions in recent years. Alongside high SO2, the volcanic plume comprised a mixture of other gases, our researchers are now investigating the composition of the plume in more detail.
Should we be concerned?
While this event exceeded air quality objectives for 10 hours in Edinburgh, it did not breach workplace exposure limits or pose a significant health risk. Our modelling effort helped predict that this plume would pass rapidly over the UK. Through chemical reactions, sulphur dioxide can contribute to the formation of small airborne particles (PM2.5) that are harmful to human health. Measurement and model results indicate that PM2.5 concentrations stayed well below levels of concern during this event.
Ecosystems are also vulnerable to sulphur dioxide. However, again the short-lived nature of the plume means that damage is likely to have been minimal.
This event will give us valuable insights into how well we can predict the impacts of volcanic eruptions on human health and our environment. This helps us both to respond at short notice, and to be prepared for future eruptions.
For further information please see the related blog.
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Notes for editors
About the SO2 spike
- The current air quality objective for SO2 is 350 µg m-3 (hourly average).
- A maximum concentration of 1161 µg m-3was reported from the AURN network at Leonard St (https://uk-air.defra.gov.uk/networks/network-info?view=aurn).
- Concentrations stayed well below the workplace exposure limit for an 8-hour shift average of 1300 µg m-3 and for 15-minute exposure of 2700 µg m-3 (https://www.hse.gov.uk/pubns/priced/eh40.pdf).
AURN Network
The Automatic Urban and Rural Network (AURN) is the UK’s largest automatic monitoring network and is the main network used for compliance reporting against the Ambient Air Quality Directives.
About UKCEH’s air quality work
Through our work in modelling and field observations, we generate long-term, high-frequency time series data of atmospheric composition change and identify contributing emission sources. These data inform development and monitoring of effective clean air policies, as well as enabling rapid responses to atmospheric events and informing how we build resilience to future events.
About SEPA’s national volcanic emissions network
SEPA’s Volcanic Emissions Network is an air monitoring network designed to detect ground level sulphur dioxide and particulate matter arriving in Scotland from volcanic activities in Iceland.
Set up in 2016 as a direct response to the 2010 Eyjafjallajökull and 2011 Grímsvötn eruptions, the VEN is a permanent air monitoring network comprising four sites across northern Scotland at Loch of Strathbeg, Tulloch Bridge, Lewis, and Orkney.
The network extends the geographical coverage of the existing air quality monitoring network in Scotland and forms part of an early warning system to better detect and report on potential effects on air quality to the Scottish Government, partners in the health sector and the public.
About EMEP4UK
The EMEP4UK is an off-line atmospheric chemistry transport model (ACTM) based on the EMEP MSC-W model, which has been developed by the co-operative programme for monitoring and evaluation of the long-range transmission of air pollutants in Europe (www.emep.int). The model EMEP4UK is capable of representing the UK hourly atmospheric composition at a horizontal scale ranging from 100 km to 1 km. The Weather Research Forecast (WRF) model was used as the main meteorological driver. Further details of the air quality forecasts from the model can be found here: http://www.emep4uk.ceh.ac.uk/
Though emission rates at the time were unknown, the EMEP4UK model (previously used in responding to volcanic fissure eruptions from Iceland), enabled us to replicate the observations across the UK and forecast how long the plume would impact UK air quality. The magnitude of the SO2 emission source added to the model was estimated from previous volcanic activities in Iceland, and were injected into the atmosphere at an altitude varying form 2 km to 1 km. At the start of the eruption the emissions were set to 15000 kg/s of SO2 for the first few hours, reduced to 5000 kg/s SO2 afterwards. The emissions magnitude used in this simulation was set to match the observed SO2 in the UK.
About Auchencorth Moss
The Auchencorth Moss Atmospheric Observatory managed and operated by UKCEH, is the largest instrumented site in Scotland for monitoring air quality. Established in 1994, the site monitors over 300 chemical and physical aspects of the atmosphere and can report near real-time information on the composition of our air, enabling us to rapidly assess air pollution events.