BrO Concentrations Research Articles

Stratospheric ozone: Impact of human activity

Current knowledge of the chemistry of the stratosphere is reviewed using measurements from the Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment to test the accuracy of our treatment of processes at mid-latitudes, and results from the Airborne Antarctic Ozone Experiment (AAOE) to examine our understanding of processes for the polar environment. It is shown that, except for some difficulties with N 2O 5 and possibly ClNO 3, gas phase models for nitrogen and chlorine species at 30°N in spring are in excellent agreement with the data from ATMOS. Heterogeneous processes may have an influence on the concentrations of NO 2, N 2O 5, HNO 3, and ClNO 3 for the lower stratosphere at 48°S in fall. Comparison of model and observed concentrations of O 3 indicate good agreement at 30°N, with less satisfactory results at 48°S. The discrepancy between the loss rate of O 3 observed over the course of the AAOE mission in 1987 and loss rates calculated using measured concentrations of ClO and BrO is found to be even larger than that reported by Anderson et al. (1989, J. geophys. Res. 94, 11480). There appear to be loss processes for removal of O 3 additional to the HOC1 mechanism proposed by Solomon et al. (1986, Nature 321, 755), the ClO-BrO scheme favored by McElroy et al. (1986, Nature 321, 759), and the ClO dimer mechanism introduced by Molina and Molina (1987, J. phys. Chem. 91, 433). There is little doubt that industrial halocarbons have a significant impact on stratospheric O 3. Controls on emissions more stringent than those defined by the Montreal Protocol will be required if the Antarctic Ozone Hole is not to persist as a permanent feature of the stratosphere.

In situ observations of midlatitude stratospheric ClO and BrO

A balloon‐borne experiment to measure midlatitude stratospheric [BrO] and [ClO] by NO chemical conversion/atomic resonance fluorescence was flown from Palestine, Texas, on 20 May 1986. In this first study of BrO, no signal attributable to BrO was detected, and upper limits (2σ uncertainty) between 35 and 24 km altitude give BrO mixing ratios less than 15 pptv. Current models predict mixing ratios that are 1.7 times larger. Measurements of [ClO] were obtained at less than .2 km altitude resolution from 41 to 22 km. The smoothly varying altitude profile lies within the range of 2‐D model calculations.

Period of homogeneous oscillations in the ferroin-catalyzed Zhabotinskii system

This work is primarily an experimental investigation of the ferroin-catalyzed Zhabotinskii system [malonic acid (MA), sulfuric acid, sodium bromate, traces of bromide ions, and ferroin]. We measure the transmittance as a function of time at 546 nm. The emphasis is placed on the properties of the period of homogeneous oscillations. It is found that T depends on the initial concentrations of reactants: T (s) = C [BrO−3]−1.60 [H2SO4]−2.70 [MA]−0.270 s (mol dm−3)4.57. The period is not perfectly constant. We investigate the conditions which favor irregularities: Low concentrations of BrO−3, H2SO4, or MA; high concentrations of catalyst or reaction products. The irregularities in the period of homogeneous oscillations are of direct interest for our understanding of the formation of waves in the distributed system. Also, we find bifurcations in which a transition from steady-state to full-blown oscillations is observed. Such bifurcations may be due to an unstable limit cycle or to a saddle-node transition. We discuss the saddle-node case in terms of the Bautin model. Finally, two steady states are observed. One of them has not been reported previously: In this state, the catalyst is mostly oxidized (blue). The oxidized steady state occurs at low [MA]0. Under the same conditions of low [MA]0, the distributed system exhibits both oxidizing (blue) and reducing (red) waves. This interesting new observation shows how much the ferroin-catalyzed Zhabotinskii system is still underinvestigated.

Kinetic studies for diatomic free radicals using mass spectrometry. Part 3.—Elementary reactions involving BrO X2Π radicals

Elementary reactions involving BrO X2Π radicals have been studied at 298 K in a discharge-flow system linked to a mass spectrometer with collision-free sampling. Detection of BrO was made directly by means of the BrO+ ion current, calibrated in terms of absolute BrO concentrations using the rapid reaction (1), NO + BrO [graphic omitted] NO2+Br.(1) Rate constants at 298 K (cm3 molecule–1 s–1) are reported for the second order decay reaction (2), BrO + BrO [graphic omitted] 2 Br + O2(2) as well as for reaction (1): k1=(2.2 ± 0.4)× 10–11; k2=(6.4 ± 1.3)× 10–12 cm3 molecule s–1. In addition, the rate constant k3 for reaction of Br 2P3/2 atoms with O3(3), has been determined at 298 K: Br + O3 [graghic omitted] BrO + O2(3), k3=(1.2 ± 0.2)× 10–12 cm3 molecule–1 s–1.