Abstract
Abstract. Volatile halogenated organic compounds containing bromine and iodine, which are naturally produced in the ocean, are involved in ozone depletion in both the troposphere and stratosphere. Three prominent compounds transporting large amounts of marine halogens into the atmosphere are bromoform (CHBr3), dibromomethane (CH2Br2) and methyl iodide (CH3I). The input of marine halogens to the stratosphere has been estimated from observations and modelling studies using low-resolution oceanic emission scenarios derived from top-down approaches. In order to improve emission inventory estimates, we calculate data-based high resolution global sea-to-air flux estimates of these compounds from surface observations within the HalOcAt (Halocarbons in the Ocean and Atmosphere) database (https://halocat.geomar.de/). Global maps of marine and atmospheric surface concentrations are derived from the data which are divided into coastal, shelf and open ocean regions. Considering physical and biogeochemical characteristics of ocean and atmosphere, the open ocean water and atmosphere data are classified into 21 regions. The available data are interpolated onto a 1°×1° grid while missing grid values are interpolated with latitudinal and longitudinal dependent regression techniques reflecting the compounds' distributions. With the generated surface concentration climatologies for the ocean and atmosphere, global sea-to-air concentration gradients and sea-to-air fluxes are calculated. Based on these calculations we estimate a total global flux of 1.5/2.5 Gmol Br yr−1 for CHBr3, 0.78/0.98 Gmol Br yr−1 for CH2Br2 and 1.24/1.45 Gmol Br yr−1 for CH3I (robust fit/ordinary least squares regression techniques). Contrary to recent studies, negative fluxes occur in each sea-to-air flux climatology, mainly in the Arctic and Antarctic regions. "Hot spots" for global polybromomethane emissions are located in the equatorial region, whereas methyl iodide emissions are enhanced in the subtropical gyre regions. Inter-annual and seasonal variation is contained within our flux calculations for all three compounds. Compared to earlier studies, our global fluxes are at the lower end of estimates, especially for bromoform. An under-representation of coastal emissions and of extreme events in our estimate might explain the mismatch between our bottom-up emission estimate and top-down approaches.
Highlights
Halogen-containing volatile organic compounds play an important role in tropospheric (Vogt et al, 1999; von Glasow et al, 2004) and stratospheric chemical cycles (Solomon et al, 1994; Salawitch et al, 2005)
Marine and atmospheric global surface concentration maps of bromoform, dibromomethane and methyl iodide calculated with the robust fit (RF) regression are shown in Fig. 4
Data are classified into coastal, shelf and open ocean regions, and are interpolated on a 1◦ × 1◦ grid
Summary
Halogen (fluorine, chlorine, bromine, iodine)-containing volatile organic compounds play an important role in tropospheric (Vogt et al, 1999; von Glasow et al, 2004) and stratospheric chemical cycles (Solomon et al, 1994; Salawitch et al, 2005). The most widely reported shortlived halogenated compounds containing bromine in both the atmosphere and the ocean are bromoform (CHBr3) and dibromomethane (CH2Br2) Together, they may contribute ∼ 15–40 % to stratospheric bromine (Montzka and Reimann, 2011), with CHBr3 considered to be the largest single source of organic bromine (Penkett et al, 1985) to the atmosphere. Seasonal variations have been observed in coastal regions (Archer et al, 2007; Orlikowska and Schulz-Bull, 2009), the database is insufficient to resolve a global temporal dependence Anthropogenic sources, such as water chlorination, are locally significant, but relatively small on a global scale (Quack and Wallace, 2003). Recent studies have revealed a missing source of ∼ 5 pptv inorganic bromine in the stratosphere, which could possibly be explained by the contribution of oceanic VSLS (Sturges et al, 2000; Sinnhuber and Folkins, 2006; Dorf et al, 2008)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
