Impacts of the 2014–2015 Holuhraun eruption on the UK atmosphere

Abstract

Abstract. Volcanic emissions, specifically from Iceland, pose a pan-European risk and are on the UK National Risk Register due to potential impacts on aviation, public health, agriculture, the environment and the economy, from both effusive and explosive activity. During the 2014–2015 fissure eruption at Holuhraun in Iceland, the UK atmosphere was significantly perturbed. This study focuses one major incursion in September 2014, affecting the surface concentrations of both aerosols and gases across the UK, with sites in Scotland experiencing the highest sulfur dioxide (SO2) concentrations. The perturbation event observed was confirmed to originate from the fissure eruption using satellite data from GOME2B and the chemical transport model, EMEP4UK, which was used to establish the spatial distribution of the plume over the UK during the event of interest. At the two UK European Monitoring and Evaluation Program (EMEP) supersite observatories (Auchencorth Moss, SE Scotland, and Harwell, SE England) significant alterations in sulfate (SO42−) content of PM10 and PM2.5 during this event, concurrently with evidence of an increase in ultrafine aerosol most likely due to nucleation and growth of aerosol within the plume, were observed. At Auchencorth Moss, higher hydrochloric acid (HCl) concentrations during the September event (max = 1.21 µg m−3, cf. annual average 0.12 µg m−3 in 2013), were assessed to be due to acid displacement of chloride (Cl−) from sea salt (NaCl) to form HCl gas rather than due to primary emissions of HCl from Holuhraun. The gas and aerosol partitioning at Auchencorth Moss of inorganic species by thermodynamic modelling confirmed the observed partitioning of HCl. Using the data from the chemical thermodynamic model, ISORROPIA-II, there is evidence that the background aerosol, which is typically basic at this site, became acidic with an estimated pH of 3.8 during the peak of the event.Volcano plume episodes were periodically observed by the majority of the UK air quality monitoring networks during the first 4 months of the eruption (August–December 2014), at both hourly and monthly resolution. In the low-resolution networks, which provide monthly SO2 averages, concentrations were found to be significantly elevated at remote “clean” sites in NE Scotland and SW England, with record-high SO2 concentrations for some sites in September 2014. For sites which are regularly influenced by anthropogenic emissions, taking into account the underlying trends, the eruption led to statistically unremarkable SO2 concentrations (return probabilities > 0.1, ∼ 10 months). However, for a few sites, SO2 concentrations were clearly much higher than has been previously observed (return probability < 0.005, > 3000 months). The Holuhraun Icelandic eruption has resulted in a unique study providing direct evidence of atmospheric chemistry perturbation of both gases and aerosols in the UK background atmosphere. The measurements can be used to both challenge and verify existing atmospheric chemistry of volcano plumes, especially those originating from effusive eruptions, which have been underexplored due to limited observations available in the literature. If all European data sets were collated this would allow improved model verification and risk assessments for future volcanic eruptions of this type.

Acid gases and aerosol measurements in the UK (1999–2015): regional distributions and trends

“…A second, but smaller pollutant episode that was captured by the AGANet occurred in September 2014, with elevated concentrations of SO 2 , HNO 3 , SO 2− 4 , NO − 3 , and NH + 4 that came from the Icelandic Holuhraun volcanic eruptions (Twigg et al, 2016). The elevated SO 2 concentration in September 2014 led to a modest increase in annual concentrations in SO 2 for 2014 (0.58 µg m −3 , cf.…”

“…UKEAP is comprised of two EMEP supersites and four component networks: precipitation network (Precip-net), NO 2 diffusion tube network (NO 2net), National Ammonia Monitoring Network (NAMN), and the Acid Gases and Aerosol Network (AGANet). At the two EMEP supersites (Auchencorth and Harwell -relocated to Chilbolton in 2016), semi-continuous hourly speciated measurements of reactive gases and aerosols are made with the MARGA system (Twigg et al, 2016). These measurements are contributing to the validation and improvement of atmospheric models, such as FRAME (Dore et al, 2015) and EMEP4UK (Vieno et al, , 2016 that are used to de-velop and provide the evidence base for air quality policies, both nationally and internationally.…”

Relationship between the 2014–2015 Holuhraun eruption and the iron record in the East GRIP snow pit

“…The 2014-2015 eruption of Holuhraun in Iceland commenced on 29 August 2014 and lasted for approximately 4 h, producing less than 1 million m 3 of lava, before the onset of the main basaltic effusive eruption on 31 August 2014, which lasted six months and ended on 28 February 2015. Long-range periodic impacts on air quality were reported in the UK, Ireland, Finland, the Netherlands, and Austria (Gíslason et al 2015;Schmidt et al 2015;Twigg et al 2016). In addition, dating these eruption events is important for the accurate absolute dating of the ice core.…”

Changing supersites: assessing the impact of the southern UK EMEP supersite relocation on measured atmospheric composition

“…Following this event there are no discernible changes in SO 2 concentration, including through the site relocation, apart from a singular peak in August 2014 which can be attributed to an Icelandic volcanic eruption (Twigg et al 2016). Whilst the emission inventory estimates greater local SO 2 emissions around Harwell than around Chilbolton (figure 3), these are overwhelmingly dominated at Harwell by Didcot B power station.…”

“…This is anticipated, as the limit of detection (LOD) of the UV fluorescence analyser (1.5 ppb, ∼4 μg m −3 ) is approximately two orders of magnitude greater than that of the MARGA (0.04 μg m −3 (Makkonen et al 2012)). The aim of the AURN SO 2 analysers is to detect pollution events (Twigg et al 2016) where concentrations could exceed national/EU limit values (hourly and daily means of 350 and 125 μg m −3 ), whereas the MARGA is designed to monitor changes in background concentrations of SO 2 . Extending the time series of SO 2 measurements at Harwell back to 2012 shows that there was a large reduction in concentrations in early 2013 ( figure 7), coincident with the closure of Didcot A coal and oil power station, which whilst operational was one of the largest SO 2 emission sources in the UK (Vieno et al 2010).…”