Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder

Caroline Womack

Research Interests

Air quality, tropospheric chemistry, cavity-enhanced spectroscopy, cavity ringdown spectroscopy, nitrogen oxides, aerosol optical properties

Current Research

My current research concerns the effect that reactive trace gases and aerosols can have on atmospheric chemistry, including the global climate and local air quality.

Wintertime particulate matter pollution: Salt Lake City, UT frequently experiences poor wintertime air quality due to its mountain terrain and meteorological episodes which trap pollutants close to the surface. In order to further understand what chemical mechanisms are involved in the buildup of aerosols in the area, I participated in the Utah Winter Fine Particulates Study (UWFPS) in Jan - Feb, 2017. We flew our custom built nitrogen oxides cavity ringdown spectrometer to measure NOx (a byproduct of fossil fuel combustion) and ozone (an air toxic) in a light aircraft throughout Salt Lake Valley area. Using this data set, we learned that the formation of ammonium nitrate aerosol is most sensitive to reductions in VOCs, not NOx as often assumed. This has implications for pollution control strategies in the valley. Read more about this campaign in our blog:

Biomass burning aerosol optical properties in controlled burns: Wildfires are increasing in intensity and frequency in the western U.S., and releasing increasing amounts of trace gas pollutants and aerosols. In order to better understand the effect these aerosols have on the climate, I participated in the first stage of the Fire Influence on Regional and Global Environments Experiment (FIREX) at the Missoula Fire Sciences Lab in Oct - Nov 2016. I was investigating the optical properties of biomass burning aerosol generated in controlled burns, using a custom build broadband cavity enhanced spectrometer.

Trace gas measurements in wildfires: During the summer of 2019, I flew the NOAA Airborne Cavity Enhanced Spectrometer (ACES), which measures NO2, glyoxal, methylglyoxal and HONO, on board the NASA DC-8 aircraft during the FIREX-AQ campaign. This campaign was designed to sample smoke from wildfires and agricultural prescribed fires with fully instrumented aircraft, mobile vans, and ground sites, in order to build a better understanding of wildfire emissions and how they transform downwind.

View Publications

  • Womack CC; Chace WS; Wang S; Baasandorj M; Fibiger DL; Franchin A; Goldberger L; Harkins C; Jo DS; Lee BH. (Feb 2023). Midlatitude Ozone Depletion and Air Quality Impacts from Industrial Halogen Emissions in the Great Salt Lake Basin. Environmental Science and Technology (Washington) , 57(5), 1870-1881. 10.1021/acs.est.2c05376
  • Womack CCC; Brown SSS; Ciciora SJ; Gao R-S; McLaughlin RJ; Robinson MA; Rudich Y; Washenfelder RA. (Nov 2022). A lightweight broadband cavity-enhanced spectrometer for NO2 measurement on uncrewed aerial vehicles. Atmospheric Measurement Techniques , 15(22), 6643-6652. 10.5194/amt-15-6643-2022
  • Bourgeois I; Peischl J; Neuman JA; Brown SS; Allen HM; Campuzano-Jost P; Coggon MM; DiGangi JP; Diskin GS; Gilman JB. (Aug 2022). Comparison of airborne measurements of NO, NO2, HONO, NOy, and CO during FIREX-AQ. Atmospheric Measurement Techniques , 15(16), 4901-4930. 10.5194/amt-15-4901-2022
  • Stockwell CE; Bela MM; Coggon MM; Gkatzelis GI; Wiggins E; Gargulinski EM; Shingler T; Fenn M; Griffin D; Holmes CD. (May 2022). Airborne Emission Rate Measurements Validate Remote Sensing Observations and Emission Inventories of Western U.S. Wildfires. Environmental Science and Technology (Washington). 10.1021/acs.est.1c07121
  • Washenfelder RA; Azzarello L; Ball K; Brown SS; Decker ZCJ; Franchin A; Fredrickson CD; Hayden K; Holmes CD; Middlebrook AM. (May 2022). Complexity in the Evolution, Composition, and Spectroscopy of Brown Carbon in Aircraft Measurements of Wildfire Plumes. Geophysical Research Letters , 49(9). 10.1029/2022GL098951
  • Bourgeois I; Peischl J; Neuman JA; Brown SS; Allen HM; Campuzano-Jost P; Coggon MM; DiGangi JP; Diskin GS; Gilman JB. (Jan 2022). Comparison of airborne measurements of NO, NO<sub>2</sub>, HONO, NO<sub>y</sub> and CO during FIREX-AQ. 10.5194/amt-2021-432
  • Liao J; Wolfe GM; Hannun RA; St Clair JM; Hanisco TF; Gilman JB; Lamplugh A; Selimovic V; Diskin GS; Nowak JB. (Dec 2021). Formaldehyde evolution in US wildfire plumes during the Fire Influence on Regional to Global Environments and Air Quality experiment (FIREX-AQ). Atmospheric Chemistry and Physics , 21(24), 18319-18331. 10.5194/acp-21-18319-2021
  • Decker ZCJ; Wang S; Bourgeois I; Campuzano Jost P; Coggon MM; DiGangi JP; Diskin GS; Flocke FM; Franchin A; Fredrickson CD. (Dec 2021). Novel Analysis to Quantify Plume Crosswind Heterogeneity Applied to Biomass Burning Smoke. Environmental Science and Technology (Washington) , 55(23), 15646-15657. 10.1021/acs.est.1c03803
  • Xu L; Crounse JD; Vasquez KT; Allen H; Wennberg PO; Bourgeois I; Brown SS; Campuzano-Jost P; Coggon MM; Crawford JH. (Dec 2021). Ozone chemistry in western US wildfire plumes. Science Advances , 7(50). 10.1126/sciadv.abl3648
  • Decker ZCJ; Robinson MA; Barsanti KC; Bourgeois I; Coggon MM; DiGangi JP; Diskin GS; Flocke FM; Franchin A; Fredrickson CD. (Nov 2021). Nighttime and daytime dark oxidation chemistry in wildfire plumes: an observation and model analysis of FIREX-AQ aircraft data. Atmospheric Chemistry and Physics , 21(21), 16293-16317. 10.5194/acp-21-16293-2021
  • Hallar AG; Brown SS; Crosman E; Barsanti KC; Cappa CD; Faloona I; Fast J; Holmes HA; Horel J; Lin J. (Oct 2021). Coupled Air Quality and Boundary-Layer Meteorology in Western U.S. Basins during Winter: Design and Rationale for a Comprehensive Study. Bulletin of the American Meteorological Society , 102(10), E2012-E2033. 10.1175/bams-d-20-0017.1
  • Womack CC; Manfred KM; Wagner NL; Adler G; Franchin A; Lamb KD; Middlebrook AM; Schwarz JP; Brock CA; Brown SS. (May 2021). Complex refractive indices in the ultraviolet and visible spectral region for highly absorbing non-spherical biomass burning aerosol. Atmospheric Chemistry and Physics , 21(9), 7235-7252. 10.5194/acp-21-7235-2021
  • Lao M; Crilley LR; Salehpoor L; Furlani TC; Bourgeois I; Neuman JA; Rollins AW; Veres PR; Washenfelder RA; Womack CC. (Nov 2020). A portable, robust, stable, and tunable calibration source for gas-phase nitrous acid (HONO). Atmospheric Measurement Techniques , 13(11), 5873-5890. 10.5194/amt-13-5873-2020
  • Moravek, A; Murphy, JG; Hrdina, A; Lin, JC; Pennell, C; Franchin, A; Middlebrook, AM; Fibiger, DL; Womack, CC; McDuffie, EE; Martin, R; Moore, K; Baasandorj, M; Brown, SS. (Dec 2019). Wintertime spatial distribution of ammonia and its emission sources in the Great Salt Lake region. ATMOSPHERIC CHEMISTRY AND PHYSICS , 19(24). 10.5194/acp-19-15691-2019
  • Adler, G; Wagner, NL; Lamb, KD; Manfred, KM; Schwarz, JP; Franchin, A; Middlebrook, AM; Washenfelder, RA; Womack, CC; Yokelson, RJ; Murphy, DM. (Sep 2019). Evidence in biomass burning smoke for a light-absorbing aerosol with properties intermediate between brown and black carbon. AEROSOL SCIENCE AND TECHNOLOGY , 53(9). 10.1080/02786826.2019.1617832
  • McDuffie, EE; Womack, CC; Fibiger, DL; Dube, WP; Franchin, A; Middlebrook, AM; Goldberger, L; Lee, B; Thornton, JA; Moravek, A; Murphy, JG; Baasandorj, M; Brown, SS. (Jul 2019). On the contribution of nocturnal heterogeneous reactive nitrogen chemistry to particulate matter formation during wintertime pollution events in Northern Utah. ATMOSPHERIC CHEMISTRY AND PHYSICS , 19(14). 10.5194/acp-19-9287-2019
  • Womack, CC; McDuffie, EE; Edwards, PM; Bares, R; de Gouw, JA; Docherty, KS; Dube, WP; Fibiger, DL; Franchin, A; Gilman, JB; Goldberger, L; Lee, BH; Lin, JC; Lone, R; Middlebrook, AM; Millet, DB; Moravek, A; Murphy, JG; Quinn, PK; Riedel, TP; Roberts, JM; Thornton, JA; Valin, LC; Veres, PR; Whitehill, AR; Wild, RJ; Warneke, C; Yuan, B; Baasandorj, M; Brown, SS. (May 2019). An Odd Oxygen Framework for Wintertime Ammonium Nitrate Aerosol Pollution in Urban Areas: NOx and VOC Control as Mitigation Strategies. GEOPHYSICAL RESEARCH LETTERS , 46(9). 10.1029/2019GL082028
  • Franchin, A, DL Fibiger, L Goldberger, EE McDuffie, A Moravek, CC Womack, ET Crosman, KS Docherty, WP Dube, SW Hoch, BH Lee, R Long, JG Murphy, JA Thornton, SS Brown, M Baasandorj and AM Middlebrook. (Dec 2018). Airborne and ground-based observations of ammonium-nitrate-dominated aerosols in a shallow boundary layer during intense winter pollution episodes in northern Utah. ATMOSPHERIC CHEMISTRY AND PHYSICS , 18(23). 10.5194/acp-18-17259-2018
  • Manfred, KM, RA Washenfelder, NL Wagner, G Adler, F Erdesz, CC Womack, KD Lamb, JP Schwarz, A Franchin, V Selimovic, RJ Yokelson and DM Murphy. (Feb 2018). Investigating biomass burning aerosol morphology using a laser imaging nephelometer. ATMOSPHERIC CHEMISTRY AND PHYSICS , 18(3). 10.5194/acp-18-1879-2018
  • Barreau, L, O Martinez, KN Crabtree, CC Womack, JF Stanton and MC McCarthy. (Aug 2017). Oxygen-18 Isotopic Studies of HOOO and DOOO. JOURNAL OF PHYSICAL CHEMISTRY A , 121(33). 10.1021/acs.jpca.7b05380
  • Womack, CC, JA Neuman, PR Veres, SJ Eilerman, CA Brock, ZCJ Decker, KJ Zarzana, WP Dube, RJ Wild, PJ Wooldridge, RC Cohen and SS Brown. (May 2017). Evaluation of the accuracy of thermal dissociation CRDS and LIF techniques for atmospheric measurement of reactive nitrogen species. ATMOSPHERIC MEASUREMENT TECHNIQUES , 10(5). 10.5194/amt-10-1911-2017