Identification of Smoke and Sulfuric Acid Aerosol in SAGE III/ISS Extinction Spectra Following the 2019 Raikoke Eruption

Abstract

Abstract. The 2019 eruption of Raikoke was the largest volcanic eruption since 2011 and it was coincident with 2 major wildfires in the northern hemisphere. The impact of these events was manifest in the SAGE III/ISS extinction coefficient measurements. As the volcanic aerosol layers moved southward, a secondary peak emerged at an altitude higher than that which is expected for sulfuric acid aerosol. It was hypothesized that this secondary plume may contain a non-negligible amount of smoke contribution. We developed a technique to classify the composition of enhanced aerosol layers as either smoke or sulfuric acid aerosol. This method takes advantage of the different spectral properties of smoke and sulfuric acid aerosol, which is manifest in distinctly different spectral slopes in the SAGE III/ISS data. Herein we demonstrate the utility of this method using 4 case-study events (2018 Ambae eruption, 2019 Ulawun eruption, 2017 Canadian pyroCb, and 2020 Australian pyroCb) and provide corroborative data from the CALIOP instrument before applying it to the Raikoke plumes. We determined that, in the time period following the Raikoke eruption, smoke and sulfuric acid aerosol were present throughout the atmosphere and the 2 aerosol types were preferentially partitioned to higher (smoke) and lower (sulfuric acid) altitudes. Herein, we present an evaluation of the performance of this classification scheme within the context of the aforementioned case-study events followed by a brief discussion of this method's applicability to other events as well as its limitations.

Stratospheric Aerosol Composition Observed by the Atmospheric Chemistry Experiment Following the 2019 Raikoke Eruption

“…In the Raikoke southern branch at low latitudes, Knepp et al (2021) use SAGE III aerosol measurements (9 data points at near-infrared, visible, and ultraviolet wavelengths) to classify many aerosols above 20 km as smoke.…”

“…In the Raikoke southern branch at low latitudes, Knepp et al. (2021) use SAGE III aerosol measurements (9 data points at near‐infrared, visible, and ultraviolet wavelengths) to classify many aerosols above 20 km as smoke. Absorption by black carbon in smoke particles was proposed to explain self‐lofting observed in the aerosols, behavior taken as proof of the presence of smoke.…”

SAGE III/ISS aerosol/cloud categorization and its impact on GloSSAC

“…For SAGE III/ISS aerosol extinction, we have an advantage of additional wavelength measurements including a longer wavelength (1544 nm) that can be used for the analyses. As noted above, while SAGE III/ISS measurements have been used in many studies, due to a reported negative bias in the 525 nm channel (Wang et al, 2020), we now apply a simple correction by spectrally interpolating extinction between 450 and 756 nm channel using Ångström exponent (Knepp et al, 2021). While the most commonly used wavelength combinations for SAGE series of measurements are 525 and 1020 nm, due to the reasons listed in section 2.1, we prefer to use a different wavelength combination of 756 and 1544.…”