Reference data set of volcanic ash physicochemical and optical properties

Abstract

Uncertainty in the physicochemical and optical properties of volcanic ash particles creates errors in the detection and modeling of volcanic ash clouds and in quantification of their potential impacts. In this study, we provide a data set that describes the physicochemical and optical properties of a representative selection of volcanic ash samples from nine different volcanic eruptions covering a wide range of silica contents (50–80 wt % SiO2). We measured and calculated parameters describing the physical (size distribution, complex shape, and dense‐rock equivalent mass density), chemical (bulk and surface composition), and optical (complex refractive index from ultraviolet to near‐infrared wavelengths) properties of the volcanic ash and classified the samples according to their SiO2 and total alkali contents into the common igneous rock types basalt to rhyolite. We found that the mass density ranges between ρ = 2.49 and 2.98 g/cm3 for rhyolitic to basaltic ash types and that the particle shape varies with changing particle size (d < 100 μm). The complex refractive indices in the wavelength range between λ = 300 nm and 1500 nm depend systematically on the composition of the samples. The real part values vary from n = 1.38 to 1.66 depending on ash type and wavelength and the imaginary part values from k = 0.00027 to 0.00268. We place our results into the context of existing data and thus provide a comprehensive data set that can be used for future and historic eruptions, when only basic information about the magma type producing the ash is known.

MOPSMAP v1.0: a versatile tool for the modeling of aerosol optical properties

“…ω 0 is correlated with the ash type, which is mainly a result of the significant variability in m i (see Fig. 16b of Vogel et al, 2017). For all ashes, ω 0 increases slightly with wavelength, typically by about 0.05 over the wavelength range shown.…”

“…However, for realistic MOPSMAP calculations valid in the longrange regime, size distributions different from the ones used Modeled wavelength-dependent optical properties for ashes from different volcanoes. More details on the ash samples are given in Table 1 of Vogel et al (2017). The colors indicate ash type: basalt is dark blue, basaltic andesite is light blue, andesite is green, dacite is orange, and rhyolite is red (see Fig.…”

“…The colors indicate ash type: basalt is dark blue, basaltic andesite is light blue, andesite is green, dacite is orange, and rhyolite is red (see Fig. 7 of Vogel et al, 2017 for reference).…”

“…The application of this non-absorbing fraction approach seems reasonable when taking into account the variability in the transparency of the particles shown in Fig. 5 of Vogel et al (2017). Due to the data set limits of MOPSMAP, particles with r > 47.5 µm are modeled as r = 47.5 µm and aspect ratios > 5 are set to 5.…”

“…close to the source Vogel et al (2017) present a data set comprising shape-size distributions of ashes from nine different volcanoes as well as wavelength-dependent refractive indices for five different ash types. The particles were collected between 5 and 265 km from the volcanoes.…”