Porous aerosol in degassing plumes of Mt. Etna and Mt. Stromboli

Abstract

Aerosols of the volcanic degassing plumes from Mt. Etna and Mt. Stromboli were probed with in situ instruments on board the Deutsches Zentrum fur Luft- und Raumfahrt research aircraft Falcon during the contrail, volcano, and cirrus experiment CONCERT in September 2011. Aerosol properties were analyzed using angular-scattering intensities and particle size distributions measured simultaneously with the Polar Nephelometer and the Forward Scattering Spectrometer probes (FSSP series 100 and 300), respectively. Aerosols of degassing plumes are characterized by low values of the asymmetry parameter (between 0.6 and 0.75); the effective diameter was within the range of 1.5-2.8 mu m and the maximal diameter was lower than 20 mu m. A principal component analysis applied to the Polar Nephelometer data indicates that scattering features of volcanic aerosols of different crater origins are clearly distinctive from angular-scattering intensities of cirrus and contrails. Retrievals of aerosol properties revealed that the particles were "optically spherical" and the estimated values of the real part of the refractive index are within the interval from 1.35 to 1.38. The interpretation of these results leads to the conclusion that the degassing plume aerosols were porous with air voids. Our estimates suggest that aerosol particles contained about 18 to 35% of air voids in terms of the total volume

In situ measurements of angular dependent light scattering by aerosols over the contiguous United States

“…To prevent the first few principal component loadings from being dominated by the large absolute variations in forward scattering intensity the analysis was performed on the natural logarithm of theF 11 values. This transformation produces a set of principal 20 components where the first component, for example, explains the largest possible relative variance in data (Shcherbakov et al, 2016). No transformation was applied to the −F 12 /F 11 measurements.…”