Abstract
Abstract. We have sampled atmospheric ice nuclei (IN) and aerosol in Germany and in Israel during spring 2010. IN were analyzed by the static vapor diffusion chamber FRIDGE, as well as by electron microscopy. During the Eyjafjallajökull volcanic eruption of April 2010 we have measured the highest ice nucleus number concentrations (>600 l−1) in our record of 2 yr of daily IN measurements in central Germany. Even in Israel, located about 5000 km away from Iceland, IN were as high as otherwise only during desert dust storms. The fraction of aerosol activated as ice nuclei at −18 °C and 119% rhice and the corresponding area density of ice-active sites per aerosol surface were considerably higher than what we observed during an intense outbreak of Saharan dust over Europe in May 2008. Pure volcanic ash accounts for at least 53–68% of the 239 individual ice nucleating particles that we collected in aerosol samples from the event and analyzed by electron microscopy. Volcanic ash samples that had been collected close to the eruption site were aerosolized in the laboratory and measured by FRIDGE. Our analysis confirms the relatively poor ice nucleating efficiency (at −18 °C and 119% ice-saturation) of such "fresh" volcanic ash, as it had recently been found by other workers. We find that both the fraction of the aerosol that is active as ice nuclei as well as the density of ice-active sites on the aerosol surface are three orders of magnitude larger in the samples collected from ambient air during the volcanic peaks than in the aerosolized samples from the ash collected close to the eruption site. From this we conclude that the ice-nucleating properties of volcanic ash may be altered substantially by aging and processing during long-range transport in the atmosphere, and that global volcanism deserves further attention as a potential source of atmospheric ice nuclei.
Highlights
The recent eruption of the Eyjafjallajokull volcano in Iceland, besides affecting aviation in Europe, raises the question about potential effects of volcanic emissions on weather and climate
The chemical composition and morphology of particles that had been previously identified as ice nuclei by FRIDGE were determined by environmental scanning electron microscopy (ESEM) combined with energy-dispersive X-ray microanalysis (EDX). 239 individual particles were analyzed in four samples that were collected on the silicon substrates during the volcanically affected days of 16–17 April and 16–17 May
Laboratory nucleation experiments on ash samples collected in the vicinity of the eruption site (Hoyle et al, 2011; Steinke et al, 2011), as well as conclusions drawn from these data, argue against a significant volcanic contribution to ice nuclei (IN) abundance
Summary
The recent eruption of the Eyjafjallajokull volcano in Iceland, besides affecting aviation in Europe, raises the question about potential effects of volcanic emissions on weather and climate. Satellite observations in the South Atlantic and North Pacific (Gasso, 2008) show that natural degassing or weakly explosive volcanoes affect low marine stratocumulus for up to 1300 km downwind by decreasing droplet effective radius and increasing visible brightness, and may add cloud cover in otherwise cloudless areas While these observations did not consider explicitly the ice-nucleating ability of the volcanic aerosol, Lidar measurements over central Europe during the advection of the Eyjafjallajokull volcanic ash plume observed a clear impact of ash on cloud glaciation (Seifert et al, 2011). Our measurements of the IN number concentration with the static vapor diffusion chamber FRIDGE (Klein et al, 2010a) presented below show a significant enhancement of atmospheric IN when the dispersed ash cloud of the Eyjafjallajokull eruption reached central Europe in April 2010 and the eastern Mediterranean in May 2010.
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