Bromine and iodine change atmospheric oxidative capacity, deplete ozone, modify NOx = (NO2 + NO) and HOx = (OH + HO2), and in turn impact air quality and human health as well as radiative forcing and climate. The radical monoxides, BrO and IO, have large structured rovibronic absorptions in the Ultraviolet-Visible (UV-Vis) spectrum which results in rapid and active photochemistry as key intermediates in the impacts listed above, and also makes them detectable to differential optical absorption spectroscopy (DOAS). This work presents measurements of BrO and IO using DOAS, particularly from aircraft, from which total gas-phase bromine and iodine, Bry and Iy, are inferred using chemical box models. The implications of these measurements are examined. Active multiphase chemistry is found to be relevant from the marine boundary layer (MBL) to the lower stratosphere (LS).
First, this work examines measurements of bromine over the western Pacific which identify a minimum in gas-phase bromine near the tropopause and quantify a stratospheric injection of 2.7 pptv of inorganic bromine to the stratosphere where it contributes to ozone loss. Heterogeneous chemical regimes are identified which can be used to understand uncertainty in inferring Bry from BrO in the tropical tropopause layer (TTL).
Next, this work examines iodine in the upper troposphere (UT) and LS. The first detection of gas-phase iodine (as IO) in the LS is presented, as is the first quantification of particulate iodine. Iodine is found to partition shparly toward the particulate phase from the troposphere to the stratosphere. Gas-phase and particulate iodine are both found to contribute significantly to ozone loss in the UT-LS.
Multiphase iodine chemistry is also found to be atmospherically relevant west of South America where layers of iodine assosciated with dust are found to lead to miniature ozone holes in the free troposphere.
Finally, this work examines the chemical coupling between bromine and aldehydes. This is found to be critical to reproducing the phase partitioning of bromine between the gas phase and sea salt aerosol in the MBL. It aslo modulates the heterogeneous chemical regimes identified earlier, not only in the TTL but also in the UT.
|Commitee:||Van Roozendael, Michel, de Gouw, Joost, Montzka, Stephen A|
|School:||University of Colorado at Boulder|
|School Location:||United States -- Colorado|
|Source:||DAI-B 81/6(E), Dissertation Abstracts International|
|Subjects:||Atmospheric Chemistry, Chemistry|
|Keywords:||Bromine, Halogens, Iodine, Marine, Spectroscopy, Stratosphere|
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