Abiotic Methyl Bromide Formation from Vegetation, and Its Strong Dependence on Temperature

Abstract

Methyl bromide (CH3Br) is the most abundant brominated organic compound in the atmosphere. It is known to originate from natural and anthropogenic sources, although many uncertainties remain regarding strengths of both sources and sinks and the processes leading to its formation. In this study a potential new CH3Br source from vegetation has been examined, analogous to the recently discovered abiotic formation of methyl chloride from plant pectin. Several plant samples with known bromine content, including ash (Fraxinus excelsior), saltwort (Batis maritima), tomato reference material (NIST-1573a), hay reference material (IAEA V-10), and also bromine enriched pectin, were incubated in the temperature range of 25-50 degrees C and analyzed for CH3Br emission using gas chromatography/mass spectrometry. All plant samples inspected showed an exponential increase in CH3Br emission as a function of temperature increase, i.e., emissions were observed to approximately double with every 5 degrees C rise in temperature. Next to temperature, it was found that emissions of CH3Br were also dependent on the bromine content of the plants. The highest CH3Br release rates were found for the saltwort which contained the highest bromine concentration. Arrhenius plots confirmed that the observed emissions were from an abiotic origin. The contribution of abiotic CH3Br formation from vegetation to the global budget will vary geographically as a result of regional differences in both temperature and bromide content of terrestrial plants.

Stable bromine isotopic composition of methyl bromide released from plant matter

“…The same reaction pathway has been suggested for bromide salts (Hamilton et al, 2003). This abiotic reaction pathway was suggested to be an important source to the atmospheric methyl halide budget (Keppler et al, 2005;Wishkerman et al, 2008).…”

“…Consequently, the use of CH3Br as a fumigant is scheduled to be phased out by 2015 under amendments to the Montreal Protocol (Montzka et al, 2011). However, methyl bromide is also released naturally from oceans (King et al, 2002), biomass burning (Andreae and Merlet, 2001), salt marshes (Rhew et al, 2000), wetlands (Varner et al, 1999), fungi (Harper, 1985), and several plant species (Gan et al, 1998, Wishkerman et al, 2008. The main sinks are believed to be uptake by oceans (Butler et al, 2007) and soils (Shorter et al, 1995) as well as reaction with OH radicals in the atmosphere (Saltzman et al, 2004).…”

Organohalogen emissions from saline environments – spatial extrapolation using remote sensing as most promising tool

“…Interestingly some compounds (CH 3 Cl, CH 3 Br) were found under dry conditions, others exclusively for moist soil (compare Table 3). The underlying formation scheme for a thermolysis production might have similarities to the pectin reaction reported by Wishkerman et al (2008) and offers a possible pathway of degradation of biotic material (e.g. algae mats) that remains in the topsoil during dry seasons.…”

“…Keppler et al (2005) highlighted the need for a better quantification of longerlived halomethanes such as CH 3 Cl and CH 3 Br from recently discovered, additional natural terrestrial sources. For example, Wishkerman et al (2008) elucidated the reaction of plant pectin with bromide forming CH 3 Br. This appears abiotically at ambient temperatures and the emissions are doubled with every 5 • C rise.…”

Bromine enrichment in marsh sediments as a marker of environmental changes driven by Grand Solar Minima and anthropogenic activity (Caminha, NW of Portugal)

“…The work from Rhew et al (2000Rhew et al ( , 2002 and all the succeeding investigation (Cox et al, 2004;Drewer et al, 2006;Manley et al, 2006;Wishkerman et al, 2008;Rhew and Mazéas, 2010;Rhew et al, 2014) highlighted that salt marshes are also sources of some potentially hazardous chemicals, amongst them, methyl bromide (CH 3 Br). CH 3 Br is a trace gas considered as the single largest carrier of bromine (Br) from the terrestrial and marine environments to the atmosphere.…”