Year of Award
Master of Science (MS)
Chemistry (Analytical/Environmental Option)
Department or School/College
Chemistry and Biochemistry
Robert Yokelson, Tony Ward
Formic acid, acetic acid, Western United States wildfires, emissions, photochemistry
University of Montana
Analytical Chemistry | Environmental Chemistry
Formic acid (HCOOH) and acetic acid (CH3COOH) are two of the most ubiquitous organic acids in the atmosphere. Chemical transport models consistently underestimate HCOOH and CH3COOH concentrations in environments including fire smoke, implying our incomplete understanding of their global budget. Emissions and secondary production of HCOOH and CH3COOH within complex mixtures in fire smoke is uncertain.
I used measurements from the NSF/NCAR C-130 aircraft during the Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE-CAN) campaign to investigate emissions and photochemical production of HCOOH and CH3COOH from smoke plumes. First, I compared two instruments to assess the quality of HCOOH measurements in smoke plumes for 15 research flights. HCOOH mixing ratios from the high-resolution time-of-flight chemical ionization mass spectrometer (HRToF-CIMS) on average are approximately 1.48 times higher than the proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) for HCOOH, and 1.36 times higher for emission passes.
Secondly, I examined emissions of HCOOH and CH3COOH through emission ratios (ERs) and emission factors (EFs) of 24 fires sampled during WE-CAN. HCOOH (HRToF-CIMS) ERs average 6.1 ± 2.6 ppb/ppmCO but show an increasing trend at 1.46 ppb/ppmCO/hour, suggesting chemical formation may have occurred prior to plume sampling by the C-130, all of which were less than two hours of physical aging since known fire locations. CH3COOH (PTR-ToF-MS) average ER is 11.5 ± 2.2 ppb/ppmCO, with an increase of 0.483 ppb/ppmCO/hour. WE-CAN derived CH3COOH EF, 2.38 ± 0.57 g/kg, is consistent with previous studies within ± 25 %, despite diversified fuel. HCOOH EFs from WE-CAN, 1.45 ± 0.57 g/kg, were larger than the 75th percentile of previous literature, likely reflecting fast chemistry in the first two hours of physical smoke age in field data.
Third, I explored the production of HCOOH and CH3COOH in smoke plumes within 6 hours of aging. HCOOH normalized excess mixing ratios (NEMR) increase moving downwind at the rate 2.23ppb/ppmCO/hour. CH3COOH increases 2.05ppb/ppmCO/hour for the first hour, but then on average decreases by -0.76ppb/ppmCO/hour, possibly due to loss processes exceeding formations.
Wielgasz, Catherine Elizabeth, "INVESTIGATION OF EMISSIONS AND CHEMISTRY OF FORMIC ACID AND ACETIC ACID IN WILDFIRE SMOKE" (2021). Graduate Student Theses, Dissertations, & Professional Papers. 11676.
© Copyright 2021 Catherine Elizabeth Wielgasz