Atmospheric Chemistry Program Seminar: Randall Chiu, CU-ANYL Chem
May
1
Mon
2023
12:15 pmMDT
Open to Public
Air-Sea Exchange of Reactive Gases: Chemistry at Interfaces and Partitioning in Aqueous Droplets
Randall Chiu,
Volkamer group,
ANYL PhD thesis
"Many puzzles remain regarding the interaction of halogens with oxygenated volatile organic compounds (OVOC) in the marine boundary layer (MBL). Observations of the OVOC glyoxal (CHOCHO) over the remote Pacific Ocean are difficult to reconcile with its brief (2-4 hour) atmospheric lifetime and high water solubility (Henry’s law constant ~4×105 M/atm). In those same airmasses, concentrations of reactive halogen species, specifically bromine monoxide (BrO) are below detection limits even though models predict up to 1.3 pptv. Presented here is a surface reaction that holds promise for explaining one or both puzzles. In the lab, fatty acids on a simulated sea surface microlayer (SML) undergo photochemical transformation to unsaturated aldehydes (2-alkenals), subsequent ozonolysis of which produces glyoxal. In a follow-up study, 2-alkenals were shown to react with Br to produce HBr in high yield. Depending on the concentration of fatty acids in SML, fatty acid photochemistry holds promise as a candidate for the missing BrO sink.
The second work presented are aircraft ozone eddy covariance (EC) flux over the Pacific Ocean during the 2023 Technical Innovation Into Iodine and GV Environmental Research (TI3GER) technical campaign. Ozone EC fluxes were measured with three independent ozone sensors of two different designs (NCAR Fast O3, a nitric oxide chemiluminescence instrument, and KIT Fast Airborne O3, a coumarin dry chemiluminescence instrument), which has not been done before. All three instruments were shown to be suitable for EC flux experiments. Particularly interesting case studies are presented in which ozone EC flux exhibits different spatial variability than water vapor EC flux. In addition, the availability of three independent EC flux measurements was used to constrain the uncertainty and limit of detection (LOD) methods in the literature."