Atmospheric bromoform at Mace Head, Ireland: Evidence for a peatland source

• Main Authors: Carpenter, L. J., Wevill, D. J., O'Doherty, S., Spain, G., Simmonds, P. G.
• Other Authors: Department of Chemistry York, UK, University of York York, UK, School of Chemistry, University of Bristol Bristol, Department of Physics NUI Galway, National University of Ireland Galway (NUI Galway)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2005
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Mace; North Atlantic
• Online Access: https://hal.science/hal-00301694; https://hal.science/hal-00301694/document; https://hal.science/hal-00301694/file/acpd-5-5935-2005.pdf

International audience In situ atmospheric observations of bromoform (CHBr 3 ) made over a 2.5 year period at Mace Head, Ireland from May 2001?December 2003, including during the NAMBLEX (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 (December?February). 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 long-range 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 0.6+0.1 in south-easterly (100?170°) air to 1.9+0.8 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 have a fetch predominantly over land, which locally is comprised of coastal peatland ecosystems (peat bogs and coastal conifer plantations), previously identified as being strong 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 ...