Airborne Measurements and Air Quality Impacts of the 2016 California Soberanes Wildfire

Emissions from biomass burning are an important source of trace gases and particles that degrade local and regional air quality, contribute to climate forcing, and have human health effects. Among the compounds emitted are greenhouse gases including carbon dioxide (CO₂) and methane (CH₄), organics such as formaldehyde (HCHO), and other harmful species including carbon monoxide (CO) and particulate matter (PM). In addition, biomass burning is a primary source of volatile organic compounds (VOCs) and nitrogen oxides (NO_x = NO + NO₂), contributing to formation of tropospheric ozone (O₃) and reduced regional air quality. Emissions of the various ozone precursors in a fire differ based on vegetation (fuel) type, fire intensity, and age of the plume, complicating the prediction of O₃ formation.

The Soberanes Fire began from an illegal campfire on 22 July 2016 in the Garrapata State Park in Monterey County, California (36.46 °N, -121.90 °W). Over the following three months, the fire burned over 132,000 acres. Presented here are aircraft measurements of CO₂, CH₄, O₃, and HCHO from five flights near and downwind of the Soberanes wildfire, collected as part of the Alpha Jet Atmospheric eXperiment (AJAX). In situ data are used to determine emission ratios (ERs), or excess mixing ratio relative to CO₂, with particular emphasis on the evolution of methane ERs over the lifecycle of the fire. In addition, measurements of NOx and O₃ from a coastal mountaintop site are presented and are used to estimate O₃ production rates during the Soberanes Fire burning period. Lastly, the extent of ozone enhancement and air quality impacts downwind of the fire will be addressed using ground-based monitoring data, the NOAA Hazard Mapping System (HMS) smoke product, and the HYSPLIT trajectory model.