Radiative Forcing Analysis of the 2018 Kīlauea Flank Eruption

Volcanic eruptions release high concentrations of sulfur dioxide (SO2), which form sulfuric acid aerosols after oxidation. Sulfuric acid aerosols reflect shortwave solar radiation, significantly reducing the amount of solar radiation reaching Earth's surface. Studying local radiative forcing resulting from volcanic eruptions can reduce the uncertainty in estimating the cooling effects of natural sulfur dioxide emissions. The 2018 Kīlauea flank eruption on the lower East Rift Zone (ERZ) and the resulting collapse of the floor of the volcanic crater released enhanced levels of SO2 and coarse material into a relatively pristine environment.

Analyzing the optical and radiative properties derived from two AErosol RObotic NETwork (AERONET) sites (Naalehu and Mauna Loa; 49 km and 34 km from Kilauea, respectively) and Interagency Monitoring of Protected Visual Environments (IMPROVE) data of aerosol composition and abundances showed the aerosols at the Naalehu site to be primarily dominated by sulfates and coarse mass. The high abundance of volcanic aerosols at Naalehu was supported by Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) modeling and satellite imagery of the plume. However, there was a weak correlation between ammonium sulfate and increases in aerosol optical depth (AOD) at the Mauna Loa site. The estimated radiative forcing effect of sulfates based on AERONET inversions at Naalehu were -1.12 ± 0.17 W/m2 per μg/m3 of SO2 mass concentration at Kīlauea. However, only 29 of these inversions were performed during the two months of measurements at Naalehu due to constraints on when they can be performed. By fitting the power law wavelength dependence of single scatter albedo and backscatter fraction, we can recalculate the radiative forcing using AOD measurements to obtain higher temporal resolution radiative forcing estimates. With higher resolution data, the radiative forcing effect of volcanic sulfates can be better constrained.