INVESTIGATION OF EMISSIONS AND CHEMISTRY OF FORMIC ACID AND ACETIC ACID IN WILDFIRE SMOKE

Author

Catherine Elizabeth WielgaszFollow

Year of Award

2021

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Chemistry (Analytical/Environmental Option)

Department or School/College

Chemistry and Biochemistry

Committee Chair

Lu Hu

Commitee Members

Robert Yokelson, Tony Ward

Keywords

Formic acid, acetic acid, Western United States wildfires, emissions, photochemistry

Publisher

University of Montana

Subject Categories

Analytical Chemistry | Environmental Chemistry

Abstract

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.

Recommended Citation

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.
https://scholarworks.umt.edu/etd/11676