Abstract
Abstract. The volcanic eruption of Grimsvötn in Iceland in May 2011 affected surface-layer air quality at several locations in Northern Europe. In Helsinki, Finland, the main pollution episode lasted for more than 8 h around the noon of 25 May. We characterized this episode by relying on detailed physical, chemical and optical aerosol measurements. The analysis was aided by air mass trajectory calculations, satellite measurements, and dispersion model simulations. During the episode, volcanic ash particles were present at sizes from less than 0.5 μm up to sizes >10 μm. The mass mean diameter of ash particles was a few μm in the Helsinki area, and the ash enhanced PM10 mass concentrations up to several tens of μg m−3. Individual particle analysis showed that some ash particles appeared almost non-reacted during the atmospheric transportation, while most of them were mixed with sea salt or other type of particulate matter. Also sulfate of volcanic origin appeared to have been transported to our measurement site, but its contribution to the aerosol mass was minor due the separation of ash-particle and sulfur dioxide plumes shortly after the eruption. The volcanic material had very little effect on PM1 mass concentrations or sub-micron particle number size distributions in the Helsinki area. The aerosol scattering coefficient was increased and visibility was slightly decreased during the episode, but in general changes in aerosol optical properties due to volcanic aerosols seem to be difficult to be distinguished from those induced by other pollutants present in a continental boundary layer. The case investigated here demonstrates clearly the power of combining surface aerosol measurements, dispersion model simulations and satellite measurements in analyzing surface air pollution episodes caused by volcanic eruptions. None of these three approaches alone would be sufficient to forecast, or even to unambiguously identify, such episodes.
Highlights
Volcanic eruptions perturb aerosol and trace gas budgets in the troposphere and stratosphere, having thereby a potential to influence the global climate, air traffic, soils and vegetation, as well as animals and humans
We aim to address the following two questions: (1) what were the physical and chemical properties of volcanic aerosol particles after being entrained into the boundary layer air, and (2) how well these particles could be separated from other natural and anthropogenic aerosol particles present in measured air masses? In addition to providing new information about long-range transported volcanic aerosol particles, we will briefly discuss the compatibility of our observations with satellite measurements and dispersion model simulations
The great majority of the elevated particle mass concentrations could be explained by coarse particles, since the PM2.5 mass concentrations remained mainly below 20 μg m−3 and PM1 mass concentrations did not show any noticeable increases during the episode
Summary
Volcanic eruptions perturb aerosol and trace gas budgets in the troposphere and stratosphere, having thereby a potential to influence the global climate, air traffic, soils and vegetation, as well as animals and humans. Volcanic ash may cause serious damage to air craft (e.g. Guffanti et al, 2009; Gislason et al, 2011), and even relatively moderate concentrations of ash particles in the middle and upper troposphere may force air traffic authorities to change flight routes or to cancel flights (Prata, 2009; Schumann et al, 2011). Both gaseous and particulate emissions by volcanoes may have adverse effects on the environment and human health (e.g. Thordarson and Self, 2003), but this is possible only when the emissions enter the boundary layer by either direct air mass transport or sedimentation.
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