Large-scale weather patterns favorable for volcanic smog occurrences on O'ahu, Hawai'i

Kilauea Volcano, located on the Island of Hawai'i, released approximately 3700 t of sulfur dioxide (SO2) per day from April 2009 through 2014. Within the atmosphere, SO2 is oxidized and converted to sulfuric-acid aerosols, and this volcanic smog is commonly referred to as vog. This study focuses on large-scale weather patterns that bring vog to O'ahu. The Hawai'i State Department of Health PM2.5 measurements were used to identify elevated vog conditions, and a total of 101 vog days were found. European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data were used to determine weather patterns. These 101 vog days were the result of 57 distinct vog events lasting from 3 h up to 4 days. The 57 events were further categorized into three large-scale weather patterns: pre-cold fronts (37 cases), upper-level disturbances (17 cases), and Kona lows (3 cases). The pre-cold front events had variable duration lasting up to 4 days, and the largest vog concentrations occurred during long-duration pre-cold front events. Trade winds did not transport vog to O'ahu. As part of this effort, ERA-Interim data were downscaled to a resolution of 10 km and then 3.3 km using the Weather Research and Forecasting (WRF) model. The downscaled reanalysis data were used as input by the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. The HYSPLIT model allowed for a visual representation of how vog is advected by large-scale wind patterns.