Characterization of Emissions of NO2 and Other Radical Sources from Biomass Burning

Biomass burning emissions are a complex mixture of numerous gas and particle phase species that can significantly affect many atmospheric processes. Emissions of NO_x and other radical precursors play a key role in controlling ozone formation, which impacts air quality and promotes secondary organic aerosol formation. Understanding the effect of these emissions on local and regional chemistry can be challenging as the composition and magnitude of the emissions change both as the fire progresses and as the plume ages. Characterizing these changes is complicated by plume inhomogeneities and potential losses of reactive species on inlets. Open path instruments that measure the total column abundance of various species directly in the open atmosphere do not suffer from inlet effects, and because the measurement integrates over vertical and horizontal inhomogeneities, the total flux of a given species can be determined without assumptions about the distribution of that species in the atmosphere.

In this work we use the University of Colorado airborne Differential Optical Absorption Spectroscopy (DOAS) instrument to characterize the fluxes of various compounds. The DOAS instrument has three channels, a direct sun (DS-DOAS) channel in the green (538-588 nm), and two zenith-sky (ZS-DOAS) channels, one in the blue (425-490 nm) and the other in the UV (320-390 nm), allowing for measurements of nitrogen dioxide (NO₂), ozone (O₃), formaldehyde (HCHO), nitrous acid (HONO), and glyoxal (CHOCHO). This instrument, along with several other remote sensing and in situ instruments, was deployed on the University of Wyoming King Air aircraft for the trace gas emission fluxes from biomass burning sources (BB-FLUX) campaign based in Boise, ID during the summer of 2018. Column abundances were determined by flights underneath the plume, and upwind legs and vertical profiles allowed for the characterization of backgrounds and wind speeds. Results from these plume intercepts, along with implications for radical chemistry and ozone formation, will be presented.