Global sea-to-air flux climatology for bromoform, dibromomethane and methyl iodide

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 (CHBr<sub>3</sub>), dibromomethane (CH<sub>2</sub>Br<sub>2</sub>) and methyl iodide (CH<sub>3</sub>I). The input of marine halogens to the stratosphere is based on observations and modeling 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 database (<a href="https://halocat.geomar.de/"target="_blank">https://halocat.geomar.de/</a>). 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 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<sup>−1</sup> for CHBr<sub>3</sub>, 0.78/0.98 Gmol Br yr<sup>−1</sup> for CH<sub>2</sub>Br<sub>2</sub> and 1.24/1.45 Gmol I yr<sup>−1</sup> for CH<sub>3</sub>I (Robust Fit/Ordinary Least Square regression technique). Contrary to recent studies, negative fluxes occur in each sea-to-air flux climatology, mainly in the Arctic and Antarctic region. "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 calculations for all three compounds. Compared to earlier studies, our global fluxes are at the lower end of estimates, especially for bromoform. An underrepresentation of coastal emissions and of extreme events in our estimate might explain the mismatch between our bottom up emission estimate and top down approaches

Iodine's impact on tropospheric oxidants: a global model study in GEOS-Chem

“…IO, OIO, I 2 ) species (SaizLopez et al, 2012b). Recent measurements from aircraft (Dix et al, 2013;Wang et al, 2015), balloons (Butz et al, 2009), mountain tops (Puentedura et al, 2012), ground stations (Lawler et al, 2014;Mahajan et al, 2010;Read et al, 2008), and cruises (Großmann et al, 2013;Jones et al, 2010;Mahajan et al, 2012) have enabled the development of global organic halogen emissions Ziska et al, 2013) and, more recently, data sets of IO observations with extensive geographical coverage (PradosRoman et al, 2015b;Wang et al, 2015).…”

Importance of seasonally resolved oceanic emissions for bromoform delivery from the tropical Indian Ocean and west Pacific to the stratosphere

“…There are different approaches in creating global bromoform emission inventories. In the bottom-up approach, emissions are extrapolated from marine and atmospheric observations in different locations (Quack and Wallace, 2003;Butler et al, 2007;Palmer and Reason, 2009;Ziska et al, 2013). The topdown approach uses chemistry transport and chemistry climate models to infer possible emission distributions that reproduce observed atmospheric abundances of VSLSs Liang et al, 2010;Ordóñez et al, 2012).…”

Deriving an atmospheric budget of total organic bromine using airborne in situ measurements from the western Pacific area during SHIVA

“…Due to the low ozone values observed in the upper troposphere in this region, low OH values and a low oxidation capacity are expected in this region resulting in prolonged lifetimes of many trace species (Kley et al, 1996;Solomon et al, 2005;Rex et al, 2014). Hossaini et al (2013) used their 3-D chemical transport model to evaluate a range of different emission inventories Liang et al, 2010;Ziska et al, 2013). For this purpose the model outputs for the different emission inventories were compared to independent atmospheric observations including the SHIVA aircraft data, and revealed that significant differences in these scenarios exist for many geographical regions including the western Pacific region.…”