Dr Anja Schmidt is an Academic Research Fellow in the Institute for Climate and Atmospheric Science. Her current work involves modelling large-scale, sulphur-rich Icelandic volcanic eruptions. Today she compares the magnitude of man-made air pollution to what the UK could experience during a large Icelandic volcanic eruption.
Since the 29 of March, high levels of air pollution are experienced across the UK. Short-term exposure to air pollution has been linked to adverse health effects ranging from an increased risk of suffering asthma attacks, sore or dry throat, sore eyes to more severe effects such as worsening of or needing treatment for pre-existing heart and lung conditions.
On twitter, I was asked to put the current air pollution episode into context with the levels of air pollution that the UK could experience due to a long-lasting volcanic eruption in Iceland. In 2011, Leeds’ researchers published a study showing that a future Laki-type eruption in Iceland could severely degrade air quality across Europe for several months as a result of long-range transport of volcanic gases and particles [download the open access study here]. You might think that volcanic ash would cause all the trouble, but in 1783-1784 Laki pumped as much sulphur dioxide gas into the atmosphere over the course of eight months as all man-made sulphur dioxide emissions globally in 2010! Once sulphur dioxide is in the atmosphere, it gets chemically converted to form tiny sulphuric acid particles – the presence of which will add to the already existing burden of (natural and man-made) particles in the atmosphere. We usually refer to these as “particulate matter” or “PM”. PM2.5 means particles smaller than 2.5 micrometers in diameter – for comparison, a human hair typically has a diameter of 70 micrometers.
Figure 1: Average daily-mean particulate matter mass concentrations (PM2.5) measured in Leeds. The chart has been put together using daily-mean measurements published by DEFRA with the average calculated over the period given in each bar. Volcanic air pollution data are from Schmidt et al. (2011) with the average change in PM2.5 calculated for the north of England based on the first three months of a Laki-type eruption. On a daily basis the amount of volcanic air pollution will vary as a result of wind direction and eruption activity.
In Figure 1, I compare the average daily-mean particulate matter concentrations (PM2.5) experienced during man-made and volcanic pollution episodes with background air pollution in Leeds (West Yorkshire, UK). On average, particulate concentrations of 14 μg/m3 are measured in Leeds, which is considered a low level of air pollution on the air quality index devised by DEFRA (Department for Environment, Food and Rural Affairs) to protect public health. Winter- and springtime pollution is generally a little higher (21 μg/m3 on average in 2013) mainly due to stagnant air masses at this time of year. Daily-mean particulate concentrations of 21 μg/m3 are still below the air quality standard of 25 μg/m3 devised by the World Health Organization to protect public health. It is clear from Figure 1 that, in Leeds, the current air pollution episode is already worse than the one the UK experienced in April 2011. In fact, on the DEFRA air quality index the levels of air pollution between 29 March and 3 April 2014 are considered high to very high. On the BBC website you can see that there are already reports of an increase in 999 calls from people experiencing breathing difficulties across the UK.
A Laki-type eruption could last for days to months, and according to my computer model calculations, particulate matter concentrations could, on average, triple in Yorkshire during the first three months of such an eruption. Of course, the level of this additional volcanic pollution would vary on a daily basis mainly due to changes in pollutant transport (wind direction) and eruption activity. Effectively, in Yorkshire and other parts of the UK, we could experience pollution on a similar level as during April 2011 (see Figure 1), but the difference is, of course, that man-made pollution episodes last days to weeks, whereas we could experience volcanic air pollution for several weeks to months.
Figure 2: Pollution reduces visibility. On a ‘clean’ day (left photograph) with particulate matter concentrations (PM2.5) of about 15 μg/m3 one can see tens of kilometres. During April 2011, the UK experiences particulate matter concentrations in excess of 45 μg/m3, which notably reduced visibility to less than five kilometres (right photograph). During the first three months of a Laki-type eruption, particulate matter concentrations experienced in the UK could be of about the same magnitude as in April 2011. Photographs taken by K.S. Carslaw (University of Leeds) in April 2011 near Burley in Wharfedale (Yorkshire, UK). Figure modified from Schmidt, A. (in press).
High levels of air pollution reduce visibility. In Figure 2, I show two photographs taken from the same viewpoint. The left photograph was taken on a day with low pollution levels (PM2.5 of about 15 μg/m3 as typical for Leeds) and the one on the right was taken on a day with moderate levels of pollution (PM2.5 of about 45 μg/m3 as was measured during the air pollution episodes in April 2011). Visibility is clearly reduced – on a ‘clean’ day one can easily see tens of kilometres far, whereas during the 2011 pollution episode visibility was reduced to less than two kilometres. The air pollution levels in 2011 were of similar magnitude as those we predict for a future Laki-type eruption (Figure 1). Just imagine the public outcry and questions asked if we were to experience several weeks of pollution that is clearly noticeable across several parts of the country. What’s more, imagine what people must have thought is going on in 1783…
In our 2011 study, we used epidemiological evidence to estimate the likely scale of premature mortality due to the increase in particulate matter air pollution due to a Laki-type eruption. We found that in the UK, up to 20,000 people could die prematurely in the first year of a Laki-type eruption. This risk may sound far-fetched and while the probability of a long-lasting eruption such as Laki in Iceland is indeed lower (one event every 200 to 500 years) than that of one of the likes of Eyjafjallajökull in 2010 (one event every five years), its impacts on society may far exceed those we experienced in 2010 after the eruption of Eyjafjallajökull.
 Schmidt, A., Ostro, B., Carslaw, K.S., Wilson, M., Thordarson, T., Mann, G.W. and Simmons, A. (2011): Excess mortality in Europe following a future Laki-style Icelandic eruption, Proceedings of the National Academy of Sciences, 108, 38, 15710-15715. (download a copy, open access)
 Schmidt, A. (in press): Volcanic gas and aerosol hazards from a future Laki-type eruption in Iceland. In: Elsevier Volume #2 of the Hazards, Disaster & Risks Series: Volcanoes