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. Halogenated very short-lived substances (VSLSs), such as bromoform( CHBr3 ), can be transported to the stratosphere and contribute to thehalogen loading and ozone depletion. Given their highly variable emissionrates and their short atmospheric lifetimes, the exact amount as well as thespatio-temporal variability of their contribution to the stratospheric halogenloading are still uncertain. We combine observational data sets withLagrangian atmospheric modelling in order to analyse the spatial andtemporal variability of the CHBr3 injection into the stratosphere forthe time period 1979–2013. Regional maxima with mixing ratios of up to0.4–0.5 ppt at 17 km altitude are diagnosed to be over Central America (1) and over the Maritime Continent–west Pacific (2), both of which areconfirmed by high-altitude aircraft campaigns. The CHBr3 maximum overCentral America is caused by the co-occurrence of convectively driven shorttransport timescales and strong regional sources, which in conjunctiondrive the seasonality of CHBr3 injection. Model results at a dailyresolution reveal isolated, exceptionally high CHBr3 values in thisregion which are confirmed by aircraft measurements during the ACCENTcampaign and do not occur in spatially or temporally averaged model fields. CHBr3 injection over the west Pacific is centred south of the Equatordue to strong oceanic sources underneath prescribed by the here-appliedbottom-up emission inventory. The globally largest CHBr3 mixing ratiosat the cold point level of up to 0.6 ppt are diagnosed to occur over theregion of India, Bay of Bengal, and Arabian Sea (3); however, no data fromaircraft campaigns are available to confirm this finding. Inter-annualvariability of stratospheric CHBr3 injection of 10 %–20 % is to a largepart driven by the variability of coupled ocean–atmosphere circulationsystems. Long-term changes, on the other hand, correlate with the regionalsea surface temperature trends resulting in positive trends of stratospheric CHBr3 injection over the west Pacific and Asian monsoon region and negative trendsover the east Pacific. For the tropical mean, these opposite regional trendsbalance each other out, resulting in a relatively weak positive trend of 0.017±0.012  ppt Br per decade for 1979–2013, corresponding to 3 % Br per decade. The overall contribution of CHBr3 together with CH2Br2 to the stratospheric halogen loading accounts for 4.7 ppt Br, in good agreement with existing studies, with 50 % and 50 % beinginjected in the form of source and product gases, respectively.

Variability and past long-term changes of brominated very short-lived substances at the tropical tropopause