A model study of the pollution effects of the first 3 months of the Holuhraun volcanic fissure: comparison with observations and air pollution effects

Abstract. The volcanic fissure at Holuhraun, Iceland started at the end of August 2014 and continued for 6 months to the end of February 2015, with an extensive lava flow onto the Holuhraun plain. This event was associated with large SO₂ emissions, amounting up to approximately 4.5 times the daily anthropogenic SO₂ emitted from the 28 European Union countries, Norway, Switzerland and Iceland. In this paper we present results from EMEP/MSC-W model simulations to which we added 750 kg s⁻¹ SO₂ emissions at the Holuhraun plain from September to November (SON), testing three different emission heights. The three simulated SO₂ concentrations, weighted with the OMI (Ozone Monitoring Instrument) satellite averaging kernel, are found to be within 30 % of the satellite-observed SO₂ column burden. Constraining the SO₂ column burden with the satellite data while using the kernel along with the three simulated height distributions of SO₂, we estimate that the median of the daily burdens may have been between 13 and 40 kt in the North Atlantic area under investigation. We suggest this to be the uncertainty in the satellite-derived burdens of SO₂, mainly due to the unknown vertical distribution of SO₂. Surface observations in Europe outside Iceland showed concentration increases up to > 500 µg m⁻³ SO₂ from volcanic plumes passing. Three well identified episodes, where the plume crossed several countries, are compared in detail to surface measurements. For all events, the general timing of the observed concentration peaks compared quite well to the model results. The overall changes to the European SO₂ budget due to the volcanic fissure are estimated. Three-monthly wet deposition (SON) of SO_x in the 28 European Union countries, Norway and Switzerland is found to be more than 30 % higher in the model simulation with Holuhraun emissions compared to a model simulation with no Holuhraun emissions. The largest increases, apart from extreme values on Iceland, are found on the coast of northern Norway, a region with frequent precipitation during westerly winds. Over a 3-month average (during SON 2014) over Europe, SO₂ and PM_2.5 surface concentrations, due to the volcanic emissions, increased by only ten and 6 % respectively. Although the percent increase of PM_2.5 concentration is highest over Scandinavia and Scotland, an increase in PM exceedance days is found over Ireland and the already polluted Benelux region (up to 3 additional days), where any small increase in particulate matter concentration leads to an increase in exceedance days.