Investigating the Impacts of Wildfires on Air Quality in the Western US
Abstract:Wildfire emissions are an important source of a wide range of trace gases and particles that can impact local, regional and global air quality, climate forcing, biogeochemical cycles and human health. In the western US, wildfires dominate over prescribed fires. However, limited sampling of wildfire emissions means western US emission estimates rely largely on data from prescribed fires, which may not be a suitable proxy for wildfire emissions. Further, interactions of wildfire emissions with urban pollution, commonly the case with California wildfires, are complex and poorly understood.
The Alpha Jet Atmospheric eXperiment (AJAX) sampled a variety of Californian wildfire plumes during 2013 and 2014. In addition to wildfire plumes, flights sample upwind, background conditions allowing for an assessment of enhancement ratios of trace gas species (carbon dioxide, methane and ozone).
This paper presents airborne measurements of multiple trace constituents downwind of a variety of Californian wildfires, with a focus on the exceptionally large Yosemite Rim wildfire during summer 2013. During its intense burning phases, the Rim wildfire was sampled by AJAX on 29 August as well as by the NASA DC-8, as part of its SEAC4RS mission, on 26 and 27 August. AJAX revisited the wildfire on 10 September when it had reached its smoldering phase. The more extensive payload of the DC-8 helped to bridge key measurements that were not available as part of the AJAX payload (e. g. carbon monoxide). The emission ratios (ER), emission factors (EF) and combustion efficiency are compared with previous wildfire studies.
Integration of AJAX data with other available datasets, such as SEAC4RS, Lidar data from the California State University Mobile Atmospheric Profiling System (CSU-MAPS), MODIS/VIIRS Fire Radiative Power (FRP) and surface ozone and meteorology measurements is explored to assess the impacts of wildfires on downwind air quality including the densely populated California central valley.