Global modeling of biogenic bromocarbons

Abstract

[1] A global three-dimensional chemical transport model has been used to simulate atmospheric bromoform using a variety of prescribed surface emission scenarios and a simple atmospheric chemistry scheme. Model simulations indicate that global emissions of bromoform calculated previously using top-down methods are too low, and emissions are likely to be significantly larger than suggested in the World Meteorological Organization's reports on the Scientific Assessment of Ozone Depletion of 1998 and 2002. Our simulations suggest that global emissions of bromoform are in the range of 400-600 GgCHBr 3 /yr and that a large proportion of emissions are situated in tropical regions. Both these factors are likely to have an important influence on estimates of the quantity of bromine transported from the surface to the lower stratosphere by short-lived bromocarbon species and its subsequent impact on ozone in this region. Further simulations including methyl bromide, bromoform and the other major short-lived bromocarbons emitted from the ocean (CH 2 Br 2 , CH 2 BrCl, CHBr 2 Cl, CHBrCl 2 ) provide estimates on the amount of reactive bromine in the troposphere and lower stratosphere derived from these compounds.

Bromocarbons in the tropical coastal and open ocean atmosphere during the 2009 Prime Expedition Scientific Cruise (PESC-09)

“…If we assume that this emission ratio of 5 is appropriate for the SE Asian region, (10 • N to 20 • S, 90 • E to 160 • E, as used by Pyle et al, 2011), and recalling that the air mass histories in the two periods of these two studies are quite similar, then we could derive an emission estimate for CHBr 3 from the regional CH 2 Br 2 emission. That value is not observationally constrained; instead we use the SEA regional CH 2 Br 2 emission from an updated version of the Warwick et al (2006) inventory (as used by Yang et al, 2014). As before, spatially uniform ocean emissions of CH 2 Br 2 are assumed in the tropics, but emissions are halved, so that the global total of 57 Gg CH 2 Br 2 /yr is more consistent with the recent studies of Liang et al (2010) and Ordonez et al (2012).…”

“…Using this method, O'Brien et al (2009) estimated a global emission of bromoform of 823-1404 Gg yr −1 (values depend inter alia on the assumed CH 2 Br 2 emissions) using data collected at Cape Verde in June 2006. This emission is much higher than estimates in Ko et al (2003) or in Warwick et al (2006). However, Pyle et al (2011) suggest that it is not reasonable to derive global emission estimates from regional data for a short-lived species such as bromoform.…”

“…It is also consistent with the recent work of Ashfold et al (2014), who estimated a total tropical CHBr 3 emission of 225 Gg yr −1 ; simply scaling this tropical number down (using the ratio of areas) to the SEA region considered here implies a CHBr 3 emission of 33 Gg yr −1 . Our estimates, and those of Pyle et al (2011) and Ashfold et al (2014), are all much less than the regional value in Warwick et al (2006). To be more confident about our emission value would require, amongst other things, improved estimates of the CH 2 Br 2 emission.…”

Airborne measurements of organic bromine compounds in the Pacific tropical tropopause layer

“…These studies have led to significant progress in modeling the VSL org contribution to the formation of stratospheric inorganic bromine (Br y ) (3,4,(6)(7)(8)(9)(10)(11). However, the scarcity of observations to constrain the emissions, the impact of deep convection, and the effect of dehydration processes limit the prediction of short-lived source gases that reach the stratosphere (3).…”

The impact of local surface changes in Borneo on atmospheric composition at wider spatial scales: coastal processes, land-use change and air quality

“…However, a local South East Asian source magnitude can be derived from the OP3 data, amounting to somewhere between 21 and 50 Gg CHBr 3 yr -1 . These are reductions compared with a previous estimate [74]. Given the importance of the Maritime Continent for global halogen sources and transport, this new range of values for the local source strength provides an important constraint on overall global emissions; our best estimate is now 382 Gg CHBr 3 yr -1 , compared with probable upper and lower limits from about 400 to 595 Gg CHBr 3 yr -1 in Warwick et al [74] and the much wider range in WMO [57].…”