Atmospheric Chemistry Program Seminar

Spectroscopic studies of oxygen and iodine using cavity enhanced extinction spectroscopy
Henning Finkenzeller, ANYL PhD thesis,
Volkamer group
"Atmospheric oxygen extinguishes approximately 2 W m-2 solar radiation in oxygen-oxygen collision-induced absorption (O2-O2 CIA). This heats the atmosphere, affects radiative transfer, and needs to be considered in atmospheric spectroscopy. The lack of O2-O2 CIA spectra below 335 nm wavelength is limiting remote sensing applications. Here we report measured spectra of the O2-O2 CIA cross-section between 297-500 nm using Cavity Enhanced Extinction Spectroscopy. Several heretofore unmeasured weak absorption bands (at 315, 328, 420, and 495 nm) are characterized for the first time in the gas phase under controlled laboratory conditions, i.e., at atmospheric pressure and variable temperature (293, 263, and 223 K). The spectra are optimized for use in hyperspectral remote sensing applications, provide opportunities to develop theory, and warrant application in radiative transfer calculations to re-assess O2-O2 CIA heating rates in the atmosphere.
Iodine is a reactive trace element in atmospheric chemistry that destroys ozone and efficiently nucleates particles. Iodine emissions have tripled since 1950 and are projected to keep increasing. While iodic acid (HIO3) is widespread and grows particles more efficiently than sulfuric acid, its gas-phase formation mechanism is unresolved. Here, in CLOUD experiments which generate iodine radicals at atmospherically relevant rates, we show that iodooxy hypoiodite, IOIO, is efficiently converted into HIO3 via reactions (R1) IOIO + O3 → IOIO4 and (R2) IOIO4 + H2O → HIO3 + HOI + O2. The laboratory derived mechanism is corroborated by theory and shown to explain field observations of daytime HIO3 in the remote lower free troposphere. The new mechanism provides a missing link between iodine sources and particle formation and - since aerosol iodate is readily reduced in the atmosphere, thereby recycling iodine back to the gas phase - suggests an important catalytic role of iodine in aerosol formation."