Pinatubo eruption. The climatic aftermath

Small-scale volcanic aerosols variability, processes and direct radiative impact at Mount Etna during the EPL-RADIO campaigns

The aerosol properties of Mount Etna’s passive degassing plume and its short-term processes and radiative impact were studied in detail during the EPL-RADIO campaigns (summer 2016–2017), using a synergistic combination of observations and radiative transfer modelling. Summit observations show extremely high particulate matter concentrations. Using portable photometers, the first mapping of small-scale (within \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim 20\,\hbox {km}$$\end{document}∼20km from the degassing craters) spatial variability of the average size and coarse-to-fine burden proportion of volcanic aerosols is obtained. A substantial variability of the plume properties is found at these spatial scales, revealing that processes (e.g. new particle formation and/or coarse aerosols sedimentation) are at play, which are not represented with current regional scale modelling and satellite observations. Statistically significant progressively smaller particles and decreasing coarse-to-fine particles burden proportion are found along plume dispersion. Vertical structures of typical passive degassing plumes are also obtained using observations from a fixed LiDAR station constrained with quasi-simultaneous photometric observations. These observations are used as input to radiative transfer calculations, to obtain the shortwave top of the atmosphere (TOA) and surface radiative effect of the plume. For a plume with an ultraviolet aerosol optical depth of 0.12–0.14, daily average radiative forcings of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$-\;4.5$$\end{document}-4.5 and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$-\;7.0\,\hbox {W/m}^2$$\end{document}-7.0W/m2, at TOA and surface, are found at a fixed location \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim 7\,\hbox {km}$$\end{document}∼7km downwind the degassing craters. This is the first available estimation in the literature of the local radiative impact of a passive degassing volcanic plume.

Drivers of solar radiation variability in the McMurdo Dry Valleys, Antarctica

Annually averaged solar radiation in the McMurdo Dry Valleys, Antarctica has varied by over 20 W m^-2 during the past three decades; however, the drivers of this variability are unknown. Because small differences in radiation are important to water availability and ecosystem functioning in polar deserts, determining the causes are important to predictions of future desert processes. We examine the potential drivers of solar variability and systematically eliminate all but stratospheric sulfur dioxide. We argue that increases in stratospheric sulfur dioxide increase stratospheric aerosol optical depth and decrease solar intensity. Because of the polar location of the McMurdo Dry Valleys (77-78°S) and relatively long solar ray path through the stratosphere, terrestrial solar intensity is sensitive to small differences in stratospheric transmissivity. Important sources of sulfur dioxide include natural (wildfires and volcanic eruptions) and anthropogenic emission.

Fluorescence imaging of microbe-containing particles shot from a two-stage Light-gas gun into an aerogel

We have proposed an experiment (the Tanpopo mission) to capture microbes on the Japan Experimental Module of the International Space Station. An ultra low-density silica aerogel will be exposed to space for more than 1 year. After retrieving the aerogel, particle tracks and particles found in it will be visualized by fluorescence microscopy after staining it with a DNA-specific fluorescence dye. In preparation for this study, we simulated particle trapping in an aerogel so that methods could be developed to visualize the particles and their tracks. During the Tanpopo mission, particles that have an orbital velocity of ~8 km/s are expected to collide with the aerogel. To simulate these collisions, we shot Deinococcus radiodurans-containing Lucentite particles into the aerogel from a two-stage light-gas gun (acceleration 4.2 km/s). The shapes of the captured particles, and their tracks and entrance holes were recorded with a microscope/camera system for further analysis. The size distribution of the captured particles was smaller than the original distribution, suggesting that the particles had fragmented. We were able to distinguish between microbial DNA and inorganic compounds after staining the aerogel with the DNA-specific fluorescence dye SYBR green I as the fluorescence of the stained DNA and the autofluorescence of the inorganic particles decay at different rates. The developed methods are suitable to determine if microbes exist at the International Space Station altitude.

Trends and sources of perchlorate in Arctic snow

Samples from the Devon Island ice cap (Nunavut, Canada) were used to calculate the annual input of atmospheric formed perchlorate. Depth samples collected in the spring of 2006 were dated between 1996 and 2005. An optimized ion chromatography tandem mass spectrometry (IC-MS/MS) method with direct injection allowed detection of perchlorate in all analyzed samples. Concentrations varied between 1 and 18 ng L(-1), showed seasonality, and were correlated with the total ozone levels from the area. A significant correlation was observed between chloride and perchlorate only for data sets corresponding to peak perchlorate concentrations. Data available suggests that perchlorate from the Arctic snow was formed in the atmosphere following two different mechanisms. Stratospheric chlorine radicals reacted with ozone year around, producing concentrations of perchlorate correlated with the total ozone level. The second pathway was specific to the summer months, when the amounts of perchlorate were correlated with the chloride concentrations, suggesting a possible tropospheric formation. Analysis of a deep ice core sample confirmed that perchlorate was present in precipitation at similar concentration more than 2000 years ago. Perchlorate ion represents a sink for the stratospheric chlorine, being removed via precipitation. The estimated amount of perchlorate that reached the Arctic in 2005 was 41-86 t.

Response of a deciduous forest to the Mount Pinatubo eruption: enhanced photosynthesis

Volcanic aerosols from the 1991 Mount Pinatubo eruption greatly increased diffuse radiation worldwide for the following 2 years. We estimated that this increase in diffuse radiation alone enhanced noontime photosynthesis of a deciduous forest by 23% in 1992 and 8% in 1993 under cloudless conditions. This finding indicates that the aerosol-induced increase in diffuse radiation by the volcano enhanced the terrestrial carbon sink and contributed to the temporary decline in the growth rate of atmospheric carbon dioxide after the eruption.