Fire emissions in the US are approximately half from Northwestern wildfires and half from

prescribed fires that burn mostly in the Southeast US (Figure 2). Wildfires burn slightly more fuel

and therefore have overall larger emissions, but prescribed fires dominate the area burned and the

number of fires. FIREX-AQ will investigate both wild and prescribed fires. Wildfires generally

result in exposures with larger pollution concentrations over larger areas, and cause both local and

regional air quality impacts. Their emissions are often transported thousands of miles and can

impact large regions of the US at a time (Figure 3). Prescribed fires are usually smaller and less

intense than most wildfires but occur more frequently and throughout the whole year. They are

usually ignited during periods that minimize population expose and air quality impacts, but can

cause regional backgrounds to increase, are generally in closer proximity to populations, and are

responsible for a large fraction of the US PM2.5 emissions. To date agricultural fire outputs are still

poorly represented in emission inventories. The overarching objective of FIREX-AQ is to

provide measurements of trace gas and aerosol emissions for wildfires and prescribed fires

in great detail, relate them to fuel and fire conditions at the point of emission, characterize

the conditions relating to plume rise, follow plumes downwind to understand chemical

transformation and air quality impacts, and assess the efficacy of satellite detections for

estimating the emissions from sampled fires.