Compositional comparison and atmospheric impacts of volatile organic compounds (VOCs) emitted from agricultural fires and wildfires measured with the NOAA Integrated Whole Air Sampling System during FIREX-AQ

Abstract:

Biomass burning smoke is composed of a complex assortment of volatile organic compounds (VOCs). VOCs may be toxic and adversely affect air quality and climate through ozone and particle formation. An extensive collection of instruments were deployed aboard the NASA DC-8 research aircraft during the NOAA/NASA Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) in summer 2019 in order to interrogate the chemical and physical properties of biomass burning emissions and subsequent chemistry.

Here we present findings utilizing the NOAA Integrated Whole Air Sampling System (iWAS) with off-line analysis of VOCs via GC-MS along with other complimentary VOC measurements and trace gases measured by the FIREX-AQ team. The NOAA iWAS system is capable of instantaneous, on-demand sampling and has fast fill rates (4-10 seconds per canister). This was critical for characterizing narrow agricultural plumes and allowed for high resolution sampling across wildfire plume transects in order to investigate possible changes in chemistry at the plume edges relative to the plume center. In total, we collected 870 wildfire and 435 agricultural smoke samples and analyzed each for over 120 VOCs, some of which are rarely measured from airborne platforms.

We will compare the VOC to CO enhancement ratios of multiple wildfires and agricultural fires and the dependencies of VOC emissions on fuel type and/or fire temperature when possible. In general, the wildfires sampled in eastern Washington had higher observed VOC mixing ratios and higher VOC/CO ratios for simple alkanes, alkenes, and aromatics. The agricultural fire emissions were more chemically diverse and, in general, had higher VOC/CO ratios for certain alkynes and oxygenated VOCs compared to the wildfires sampled. Acetonitrile (ACN), a commonly used biomass burning tracer, had a wide range of observed enhancement ratios from 3.3 to 0.5 ppb ACN/ppm CO for wildfires and agricultural fires, respectively. We have identified several biomass-burning specific VOC pairs, such as the propenenitrile-to-propanenitrile ratio, that may be used to interrogate intra-plume oxidation. Lastly, we will compare the various contributions of VOCs to the VOC-OH reactivity of biomass burning emissions as a proxy for potential ozone formation.