Constraining Emission and Chemistry of Formic and Acetic Acids from Fire Smoke with WE-CAN Field Observations

Formic and acetic acids are two of the most important and abundant organic acids in the atmosphere, as both are major sources of atmospheric acidity. Their global sources are not well understood, evidenced by the incapability of models to reproduce their observations in different environments. Biomass burning is estimated to be a large but highly uncertain source of both acids, which are thought to be mostly formed during photochemical processes. We will present formic acid and acetic acid measurements made with a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) aboard the NSF/NCAR C-130 aircraft during the Western wildfire Experiment for Cloud chemistry, Aerosol absorption and Nitrogen (WE-CAN) campaign. WE-CAN is scheduled to sample up to 110 hours over the western United States in July – August 2018 to understand chemistry and emissions of wildfire smoke. We will interpret organic acid observations along with a suite of chemical species via a photochemical box model (Framework for 0-D Atmospheric Modeling (F0AM) v3.1); this will be in terms of our current understanding of primary emissions and chemical formations of formic acid and acetic acid within wildfire plumes. Both explicit and lumped chemical mechanisms (Master Chemical Mechanism and GEOS-Chem) will be tested against observed organic acids in the first day of evolution of wildfire plumes. We will predict downwind plume chemistry, calculate emission factors for organic acids, and discuss the importance of different precursors and potential missing chemical pathways for the formation of organic acids in fire smoke.