The canonical model of stratospheric volcanic SO
2 gas-to-particle conversion assumes a sulfur-gas-only precursor followed by gradual increase in sulfate-particle mass at the expense of the initial SO2 loading. However there is abundant evidence that this model is incomplete. However, the extent to which our understanding is incomplete is even now unknown. What is known is that volcanic eruptions in the satellite era—big (e.g. Pinatubo and El Chichon) and small (e.g. Nabro)—generally exhibit an immediate formation or existence of sulfate particles. The mass of these sulfate plumes has never been methodically quantified, unlike the initial SO
2 mass. However, it can be shown that indicators of sulfates from the get-go in relatively recent, mild volcanic events like Nabro (Penning de Vries et al., 2014) are manifest in many nascent volcanic clouds of major eruptions. An example of the young sulfate plume—formed during El Chichon’s 1982 event-- is shown in Figure 1. Robock and Matson (19??) tracked this “dust veil” around the globe from the very first post-eruption days. The satellite signal that unites the El Chichon plume with Nabro is the UV-backscatter-based scattering aerosol index, a quantity as accessible as the more “popular” absorbing aerosol index (used for ash detection). The UV scattering aerosol index shows unmistakable signs of hours-to-days-old sulfates, corroborated by visible satellite imagery, in many eruption plumes in the satellite era. We will survey the satellite-era eruptions (since 1979) and synergize more recent satellite data to constrain the nature and abundance of sulfates from the get-go. We will also make first-order attempts to estimate the mass and concentration of these young sulfate plumes in the quest to complete the total sulfur budget in certain historical stratospheric volcanic events.
References
Penning de Vries, M. J. M., Dörner, S., Puķīte, J., Hörmann, C., Fromm, M. D., and Wagner, T.: Characterization of a stratospheric sulfate plume from the Nabro volcano using a combination of passive satellite measurements in nadir and limb geometry, Atmos. Chem. Phys., 14, 8149-8163, https://doi.org/10.5194/acp-14-8149-2014, 2014.
Robock, A. and M. Matson, Circumglobal Transport of the El Chichón Volcanic Dust Cloud, Science, 221, 195-197, DOI: 10.1126/science.221.4606.195,1983.
Figure 1. Nimbus 7 TOMS Scattering Aerosol Index for El Chichon eruption cloud on 5-6 April 1982 (bottom, l-r). Color scale is for negative values, proportional to scattering aerosol optical depth. Upper left: TOMS SO2. Upper right: schematic of UVAI departures from zero. Positive values are for absorbing AI (e.g. ash). Negative values are the scattering-aerosol index (liquid sulfates).
