Atmospheric bromoform at Mace Head, Ireland: seasonality and evidence for a peatland source

Abstract

Abstract. In situ atmospheric observations of bromoform (CHBr 3 ) made over a 2.5 year period at Mace Head, Ireland from May 2001-Dec 2003, including during the NAM-BLEX (North Atlantic Marine Boundary Layer Experiment) campaign, show broad maxima from spring until autumn and winter minima, with mixing ratios of 5.3+1.0 pptv (mid March -mid October) and 1.8+0.8 pptv (DecemberFebruary). This indicates that, unlike CHCl 3 , which has a summer minimum and winter maximum at Mace Head, local biological sources of CHBr 3 have a greater influence on the atmospheric data than photochemical decay during longrange transport. The emission sources are predominantly macroalgal, but we find evidence for a small terrestrial flux from peatland ecosystems, which so far has not been accounted for in the CHBr 3 budget. Sharp increases in CHCl 3 and CHBr 3 concentrations and decreases in O 3 concentrations occurred at night when the wind direction switched from an ocean-to a land-based sector (land breeze) and the wind speed dropped to below 5 ms −1 . These observations infer a shallow atmospheric boundary layer with increased O 3 deposition and concentration of local emissions of both CHCl 3 and CHBr 3 . The ratio of CHCl 3 / CHBr 3 varied strongly according to the prevailing wind direction; from 0.60+0.15 in south-easterly (100-170 • ) and northerly (340-20 • ) air to 2.5+0.4 in north-easterly (40-70 • ) air. Of these land-sectors, the south-easterly air masses are likely to be strongly influenced by macroalgal beds along the coast and the emission ratios probably reflect those from seaweeds in addition to land sources. The north-easterly airmasses however had an immediate fetch inland, which locally is comprised of coastal peatland ecosystems (peat bogs and coastal conifer plantations), previously identified as being strongCorrespondence to: L. J. Carpenter (ljc4@york.ac.uk) sources of atmospheric CHCl 3 under these conditions. Although we cannot entirely rule out other local land or coastal sources, our observations also suggest peatland ecosystem emissions of CHBr 3 . We use correlations between CHCl 3 and CHBr 3 during the north-easterly land breeze events in conjunction with previous estimates of local wetland CHCl 3 release to tentatively deduce a global wetland CHBr 3 source of 20.4 (0.4-948) Gg yr −1 , which is approximately 7% of the total global source.

Short-lived brominated hydrocarbons – observations in the source regions and the tropical tropopause layer

“…This value is in good agreement with other published data from coastal mid-latitude sites, as the 0.15 determined for measurements at Mace Head (Carpenter et al, 2003) and 0.14 derived from measurements in the seacoast region of New Hampshire (Zhou et al, 2008). The results for the TransBrom IAU data indicate a higher slope of 0.25 for the two species, which can be explained by a stronger impact of chemical decay on the concentration ratios.…”

“…The results for the TransBrom IAU data indicate a higher slope of 0.25 for the two species, which can be explained by a stronger impact of chemical decay on the concentration ratios. Following Carpenter et al (2003) a correlation according to Eq. (5) was investigated to evaluate the impact from degradation processes.…”

Very short-lived bromomethanes measured by the CARIBIC observatory over the North Atlantic, Africa and Southeast Asia during 2009–2013

“…Carpenter et al, 2005). However, it is uncertain as to whether a seasonal cycle in CHBr 3 , or other VSLB, would be present in the upper troposphere or the regions sampled in this study.…”

Transport of short-lived species into the Tropical Tropopause Layer

“…Such mixing ratios have generally been observed only where sources are nearby, and are double what might be regarded as "background" levels (e.g. CHBr 3 measurements reported by Yokouchi et al, 2005;Carpenter et al, 2005;Zhou et al, 2008;Pyle et al, 2011).…”