Bromine monoxide (BrO) is important in the catalytic destruction of stratospheric ozone, especially in the lower stratosphere (below about 20 km).
Model studies indicate that catalytic cycles involving BrO may account for as much as 60% of ozone loss for very cold Arctic winters. Bromine
monoxide is the main daytime constituent of stratospheric inorganic bromine (Bry), making up about 50% of Bry. The other Bry constituents are Br, HOBr,
BrONO2, HBr, and BrCl. In contrast, for stratospheric inorganic chlorine (Cly), the reactive constituents (Cl and ClO) make up only a few percent of Cly.
To quantify the impact of inorganic bromine on stratospheric ozone loss, accurate measurements of its abundance are needed. However, because of their low abundances (several ppt),
relatively few measurements have been made of its constituents. Therefore Bry is typically estimated from
stratospheric measurements of BrO, combined with estimates of the other constituents from photochemical models. One current problem is that
estimates of Bry from measurements of stratospheric BrO obtained by various satellite and balloon-borne instruments show some disagreement.
A second current problem is that estimates of Bry from measurements of stratospheric BrO tend to exceed predictions of Bry based on measurements
of the organic source gases from which Bry is believed to be derived (CH3Br and halons). It is currently strongly suspected that there may be
additional sources of stratospheric inorganic bromine.
The BrO Molecule
How it is part of MLS Science Objectives
One of the objectives for MLS and the Aura mission is to understand and monitor changes in the chemistry and atmospheric composition that can affect stratospheric ozone. Measurements of stratospheric BrO, the dominant form of bromine in the stratosphere and the dominant form of bromine directly involved in ozone destruction, will help quantify the contribution of Bry to ozone loss.
How EOS MLS measures BrO
The standard product for BrO is taken from the 640-GHz retrieval. The spectral signature of BrO in the MLS radiances is very small, leading to a poor signal to noise ratio on individual MLS observations. Some form of averaging (e.g. monthly zonal means) is required to obtain scientifically useful results.
Quick Product Information for Data Version v4.2
- Swath Name: BrO
- Status Flag: Only use profiles for which the Status field is an even number.
- Useful Range: 10 – 3.2 hPa (day/night dierences needed)
- DAAC Short Name: ML2BRO
- Precision: Only use values for which the estimated precision is a positive number.
- Quality Threshold: >1.3
- ConvergenceThreshold: <1.05
|Download EOS Aura MLS BrO v4.2 data