Laboratory studies and in situ stratospheric observations of inorganic chlorine and bromine species critical to catalytic ozone destruction

Studies of inorganic chlorine and bromine compounds, which play pivotal roles in stratospheric ozone depletion, are presented. Chlorine species are measured with the Harvard Halogen flight instrument by detecting their constituent Cl atoms using a thermal dissociation, resonance fluorescence technique. Thermodynamic and kinetic analyses establish that ClO, ClOOCl, and ClONO₂ can each be uniquely measured in the flight instrument. Accurate calibration of the chlorine axes is critical.; The first ClOOCl measurements ever obtained in the atmosphere, acquired as part of the SOLVE flight mission to Kiruna, Sweden, are presented, thereby verifying the existence and quantifying the role of ClOOCl in polar ozone loss. A photochemical steady-state analysis is used to evaluate ClOOCl reaction rate constants. Chlorine activation was monitored throughout the polar winter for the first time, decreasing from ∼80% in late January and early February to less than 50% by mid-March. The intravortex inorganic chlorine budget shows agreement of 91% for the first SOLVE ER-2 deployment and 79% for the second; the average extravortex budget agreement is 70%.; The historically used 8-reaction kinetic model, required to convert the Cl concentrations observed in flight to actual chlorine species concentrations, is found, insufficient. Three additional reactions involving ClOO formation and loss via NO are demonstrated to be important via modeling and a laboratory kinetics study. This suggests that the ClO values from all past flight missions have a temperature-dependent low bias.; A new RF axis for bromine was designed and flown in the SOLVE mission. BrO was detected with greater sensitivity, selectivity, and spatial resolution than ever before.; The first spectra of the A 2Π_3/2 ← X 2Π_3/2 electronic transition of BrO using Fourier transform UV spectroscopy were obtained. Vibrational spectra acquired at 298 and 228 K have highly accurate wavenumbers and relative cross sections. Using a Birge-Sponer extrapolation with Le Roy-Bernstein theory, the dissociation energy and thereby the heat of formation of BrO(g), Δ_f H°(298.15 K) = 126.2 ± 1.7 kJ/mol, are determined. Modeling high-resolution rotational spectra of the 7,0 and 12,0 bands of BrO yields improved band origins, rotational constants, centrifugal distortion constants, linewidths, and lifetimes.