Stratospheric HBr concentration profile obtained from far-infrared emission spectroscopy (original) (raw)
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A Model Study of the Potential Role of the Reaction BrO+OH in the Production of Stratospheric HBr
We have used a constrained one-dimensional photochemical model to investigate the effect of a potential minor channel of the fast reaction between BrO -{-OH to produce HBr. There is no direct evidence for this reaction but the analogous yield of HC1 from C10 + OH is thought to be about 5%. With only a 1-2% yield of HBr the modelled HBr mixing ratio between 20-30 km increases from around 0.5 parts per 10 •' by volume (pptv) to 1-2 pptv. This brings the model into agreement with recent balloonborne observations of stratospheric HBr. Should BrO + OH produce HBr with around 1-2% yield then this reaction will dominate HBr production between 20-35 km. As the main loss of HBr is reaction with OH this will lead to steady state HBr:BrO partitioning which is independent of other species, and temperature.
Geophysical Research Letters, 2000
Stratospheric BrO was spectroscopically monitored by its UV absorption in direct sunlight on 8 balloon flights that were conducted at middle and high latitudes in 1996 through 2000 [e.g., Ferlemann et al.,1998, 2000]. For conditions where detailed photochemical model calculations [Chipperfield, 1999] correctly predict other measured chemical (e.g., NO2, O3) and dynamical (e.g. N2O, F12, et cetera) tracers, the total stratospheric bromine (organic and inorganic) amount (Bry) is inferred. An excellent agreement between measured and modeled stratospheric BrO is found, assuming JPL‐97 kinetics and Bry=20 ppt in the photochemical model. As the BrO absorption cross section (σBrO) is the only external parameter used in the measurement, our finding tightly constrains the amount of total inorganic bromine (Bryin), 20±2.5 ppt above 25 km in 1996/97, as well as the photochemistry of stratospheric bromine.
Sensitivity of ozone to bromine in the lower stratosphere
Geophysical Research Letters, 2005
Measurements of BrO suggest that inorganic bromine (Br y) at and above the tropopause is 4 to 8 ppt greater than assumed in models used in past ozone trend assessment studies. This additional bromine is likely carried to the stratosphere by short-lived biogenic compounds and their decomposition products, including tropospheric BrO. Including this additional bromine in an ozone trend simulation increases the computed ozone depletion over the past ~25 years, leading to better agreement between measured and modeled ozone trends. This additional Br y (assumed constant over time) causes more ozone depletion because associated BrO provides a reaction partner for ClO, which increases due to anthropogenic sources. Enhanced Br y causes photochemical loss of ozone below ~14 km to change from being controlled by HO x catalytic cycles (primarily HO 2 +O 3) to a situation where loss by the BrO+HO 2 cycle is also important.
Long-term observations of stratospheric bromine reveal slow down in growth
Geophysical Research Letters, 2006
1] The total stratospheric inorganic bromine burden (Br y ) was derived from balloon-borne bromine monoxide (BrO) observations performed with the LPMA/DOAS (Limb Profile Monitor of the Atmosphere/Differential Optical Absorption Spectroscopy) balloon payload in the last ten years. The measurements show that significantly more ozone-depleting bromine ((4.1[or 4.3] ± 2.5) ppt) reaches the stratosphere than the atmospheric transport of the major stratospheric bromine source gases, methyl bromide (CH 3 Br) and all halons can account for. The major contributors to this discrepancy are varying amounts of bromine tied in inorganic gases, particulate matter and very short-lived substances (VSLS) of natural origin. Despite the significant contribution of stratospheric bromine from natural processes, international protocols introduced to limit the production of brominated gases have been effective by slowing down the overall growth of Br y .
Climatology of the stratospheric BrO vertical distribution by balloon-borne UV–visible spectrometry
Journal of Geophysical Research, 2002
1] A balloon-borne UV-visible spectrometer, the SAOZ-BrO, has been designed for the measurement of BrO on small and relatively low-cost balloons. It allows the retrieval of the vertical BrO profile with a resolution of 1 km, a precision of 0.5-2 pptv (below 25 km), and a +5/À10% accuracy during the daytime balloon ascent. Fifteen successful flights have been carried out since 1997. Significant BrO amounts were observed at all latitudes and seasons, with a peak concentration altitude varying from 15 km in the winter vortex to 22 km in the tropics. The mixing ratio increases steadily from the tropopause to 25-30 km, depending on the latitude, above which it remains constant up to 30 km. The latitudinal and seasonal changes (maximum at high latitude and in the winter) are largely controlled by the vertical transport of total inorganic bromine and to a smaller extent by photochemistry. Photochemical changes are primarily related to NO 2 abundances. On a constant potential temperature surface, the BrO mixing ratio is the largest in Polar Regions in the winter, where NO 2 is nearly absent. In contrast, BrO is the smallest during the polar day and in the summer at midlatitude. The presence of activated chlorine in the cold vortex has little impact on BrO abundances. Finally, significant amounts were observed in the upper troposphere: (1) in the summer at midlatitude where it was the result of a stratosphere-troposphere exchange (STE) event advecting bromine from the stratosphere and (2) at the tropics where its presence is likely due to the conversion of organic bromine at lower altitude. Citation: Pundt, I., J.-P. Pommereau, M. P. Chipperfield, M. Van Roozendael, and F. Goutail, Climatology of the stratospheric BrO vertical distribution by balloon-borne UV -visible spectrometry,
Measurement of stratospheric HBr using high resolution far infrared spectroscopy
Geophysical Research Letters, 1995
Far infrared spectral features of HBr have been observed in the stratospheric emission spectrum using a balloon borne high resolution Fourier transform spectrometer equipped with a high sensitivity detector specially designed for this purpose. The value of 1.6 + 0.6 parts per trillion in volume for the HBr mixing ratio has been retrieved, from the global-fit analysis of 12! spectra, in the 25-36.5 km altitude range. The result is briefly compared with models and previous assessments.
Heterogeneous atmospheric bromine chemistry
Journal of Geophysical Research: Atmospheres, 1996
This paper considers the effect of heterogeneous bromine reactions on stratospheric photochemistry. We have considered reactions on both sulfate aerosols and on polar stratospheric clouds (PSCs). It is shown that the hydrolysis of BrONO2 on sulfate aerosols enhances the HOBr concentration, which in turn enhances the OH and HO2 concentrations, thereby reducing the HC1 lifetime and concentration. The hydrolysis of BrONO2 leads to a nighttime production of HOBr, making HOBr a major nighttime bromine reservoir. The photolysis of HOBr gives a rapid increase in the OH and HO2 concentration at dawn, as was recently observed by $alawitch et al. [1994]. The increase in the OH and HO2 concentration, and the decrease in the HC1 concentration, leads to additional ozone depletion at all latitudes and for all season. At temperatures below 210 K the bulk phase reaction of HOBr with HC1 in sulfate aerosols becomes important. The most important heterogeneous bromine reactions on polar stratospheric clouds are the mixed halogen reactions of HC1 with HOBr and BrONO2 and of HBr with HOC1 and C1ONO2. Therefore, the heterogeneous reactions considerably perturb the chlorine partitioning. In contrast, because bromine species are short-lived heterogeneous bromine reactions are important as they allow the formation of catalytic cycles for the conversion of H20 into HOx (=OH+HO2), HC1 into C10 and NOx (=NO+NO2) derived from ozonesondes [Logan, 1994]. This paper into HNO3, as well as for the rapid recycling of the shows that at least part of this ozone loss is likely to be bromine reservoir species BrONO2 and HBr. This leads due to in situ heterogeneous bromine reactions. to ozone loss at all latitudes and for all seasons, partic-The atmospheric chemistry of reactive bromine species u!arly when high loadings of sulfate aerosol are present is characterized by their short lifetimes. The longestlived reactive bromine species is HBr, which has a lifetime of up to a day but constitutes only a small fraction of the total reactive bromine (BrOy) present in the atmosphere [Lary, 1995]. In contrast, the longest-lived reactive chlorine species is HC! which typically has a lifetime of over a week in the lower stratosphere and often constitutes the largest fraction of the total reactive chlorine (ClOy) present in the atmosphere. Heterogeneous chlorine reactions are important because they provide a mechanism, not provided by gas
Gas Phase Atmospheric Bromine Photochemistry
This paper reviews the current knowledge of gas phase bromine photochemistry and presents a budget study of atmospheric bromine species. The effectiveness of the ozone catalytic loss cycles involving bromine is quantified by considering their chain length and effectiveness. The chain effectiveness is a new variable defined as the chain length multiplied by the rate of the cycle's rate-limiting step. The chain effectiveness enables a fair comparison of different catalytic cycles involving species which have very different concentrations. This analysis clearly shows that below 25 km the BrO/C10 and BrO/HO2 cycles are among the most important ozone destruction cycles.
Comparison of measurements and model calculations of stratospheric bromine monoxide
Journal of Geophysical Research, 2002
1] Ground-based zenith sky UV-visible measurements of stratospheric bromine monoxide (BrO) slant column densities are compared with simulations from the SLIMCAT three-dimensional chemical transport model. The observations have been obtained from a network of 11 sites, covering high and midlatitudes of both hemispheres. This data set gives for the first time a near-global picture of the distribution of stratospheric BrO from ground-based observations and is used to test our current understanding of stratospheric bromine chemistry. In order to allow a direct comparison between observations and model calculations, a radiative transfer model has been coupled to the chemical model to calculate simulated slant column densities. The model reproduces the observations in general very well. The absolute amount of the BrO slant columns is consistent with a total stratospheric bromine loading of 20 ± 4 ppt for the period 1998-2000, in agreement with previous estimates. The seasonal and latitudinal variations of BrO are well reproduced by the model. In particular, the good agreement between the observed and modeled diurnal variation provides strong evidence that the BrO-related bromine chemistry is correctly modeled. A discrepancy between observed and modeled BrO at high latitudes during events of chlorine activation can be resolved by increasing the rate constant for the reaction BrO + ClO ! BrCl + O 2 to the upper limit of current recommendations. However, other possible causes of the discrepancy at high latitudes cannot be ruled out. INDEX TERMS: 0340 Atmospheric Composition and Structure: Middle atmosphere-composition and chemistry; 0394 Atmospheric Composition and Structure: Instruments and techniques Citation: Sinnhuber, B.-M., et al., Comparison of measurements and model calculations of stratospheric bromine monoxide,
Role of the BRO + HO2reaction in the stratospheric chemistry of bromine
Geophysical Research Letters, 1992
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