Emissions and chemistry of formaldehyde in biomass burning plumes

Biomass burning generates a wide variety of reactive volatile organic compounds (VOC). Chemical transformations of these VOC fuel the downwind production of ozone, aerosol, and other byproducts relevant to air quality and climate. Roughly half of biomass burning VOC emissions are not measured, however, and observations of long-term plume evolution are sparse. Formaldehyde (HCHO) is a major product of this chemistry and can serve as an integrated constraint on VOC reactivity across the lifetime of a biomass burning plume. HCHO is also directly emitted by fires and can be a dominant radical source. Furthermore, as one of the few hydrocarbons detectable via UV-based remote sensing, HCHO can provide a unique perspective on regional and global impacts of biomass burning.

With dual roles as both a primary emission and secondary product, HCHO is central to the evolution and impacts of biomass burning plumes. We propose a three-phase research program focused on HCHO observations.

I. We will evaluate the chemical evolution of California�??s 2013 Rim Fire using a combination of airborne measurements, trajectory analysis and photochemical box modeling. Specific questions include:

�?� What are the primary radical sources in the plume?

�?� Can we constrain the reactivity of unquantified VOC?

�?� What is the chemical lifetime of the plume?

II. We will deploy the NASA in situ airborne formaldehyde (ISAF) instrument on the NOAA WP-3D as part of the summer 2018 FIREX field intensive. This mission will develop the targeted dataset needed to characterize the emissions and chemical evolution of North American fires.

III. We will analyze observations collected during FIREX. Many of the questions from the first task are also relevant here, and we will build off of experience and tools developed in our Rim Fire case study. Several additional tasks are proposed that will capitalize on the rich FIREX dataset, including 1) evaluation of chemical mechanisms with a highly-constrained 0-D box model, 2) improvement of orbital HCHO column retrievals over fires and their application to estimates of reactive VOC emissions, and 3) assessment of regional model performance.