The BIRA-IASB BrO Product

Tropospheric bromine monoxide (BrO)

Reactive bromine in the atmosphere

DOAS BrO Retrievals

BrO Product Validation

On-going developments

Reactive bromine in the atmosphere

Bromine monoxide (BrO) is a key trace species in the ozone chemistry because of its large efficiency as catalyst of the ozone destruction. In the polar stratosphere, its role has been studied for a long time after the suggestion of the BrO-ClO cycle by McElroy et al. [1986]. Recent findings indicate that the halogen induced O3 loss chemistry where the ClO-BrO cycle is responsible for approximately 50% of the seasonal spring O3 destruction is now largely understood [Chipperfield and Pyle, 1998]. However the continued increase of bromine loading in the stratosphere while chlorine load has reached a maximum around 1997 is still a matter of concern as it could cause the abundance of equivalent chlorine to decline more slowly than predicted.

It has long been assumed that reactive halogen species were confined to the stratosphere, playing a significant role only in polar region during spring. However, during the last few years, significant amounts of BrO were also observed in the troposphere first by ground-based instruments and more recently from space by the Global Ozone Monitoring Experiment (GOME) [Wagner and Platt, 1998; Richter et al., 1997]. The mechanisms responsible for the production of reactive bromine in both the boundary layer and in the free-troposphere are not well understood at the moment, although the role of sea-ice and sea-salt aerosol has been clearly identified. Nevertheless, at the levels (up to 100 ppt) produced in the polar boundary layer during the so-called "polar spring bromine explosion events", it is clear that BrO has a strong impact on the tropospheric chemistry, being responsible for complete removal of the ozone within hours or days - the "Polar Tropospheric Ozone Hole". Furthermore, the accumulating evidence for the presence of BrO (at levels around 1-3 ppt) in the free-troposphere of polar regions but also at mid-latitude, raises the question of the possible impact of reactive halogens on the tropospheric chemistry at the regional scale or even more widespread.