A model study of the pollution effects of the first three 1 months of the Holuhraun volcanic fissure : comparison with 2 observations and air pollution effects 3 4

11 The volcanic fissure at Holuhraun, Iceland started at the end of August 2014 and continued 12 for six months to the end of February 2015, with an extensive lava flow onto the Holuhraun 13 plain. This event was associated with large SO2 emissions, amounting up to approximately 4.5 14 times the daily anthropogenic SO2 emitted from the 28 European Union countries, Norway, 15 Switzerland and Iceland. In this paper we present results from EMEP/MSC-W model 16 simulations where we added 750 kgs SO2 emissions at the Holuhraun plain from September 17 to November (SON), testing three different emission heights. The three simulated SO2 18 concentrations, weighted with the OMI satellite averaging kernel, are found to be within 30% 19 of the satellite observed SO2 column burden. Constraining the SO2 column burden by the 20 satellite data, while using the kernel along with the three simulated height distributions of 21 SO2, we estimate that the median of the daily burdens may have been between 13 and 40 kt in 22 the North Atlantic area under investigation. We suggest this to be the uncertainty in the 23 satellite derived burdens of SO2, mainly due to the unknown vertical distribution of SO2. 24 Surface observations in Europe outside Iceland showed concentration increases up to >500 25 μgm SO2 from volcanic plumes passing. Three well identified episodes, where the plume 26 crossed several countries, are compared in detail to surface measurements. For all the events, 27 the general, timing of the observed concentration peaks compared quite well to the model 28 results. The overall changes to the European SO2 budget due to the volcanic fissure are 29