Drivers of diel and regional variations of halocarbon emissions from the tropical North East Atlantic

• Published in: Atmospheric Chemistry and Physics
• Main Authors: H. Hepach, B. Quack, F. Ziska, S. Fuhlbrügge, E. L. Atlas, K. Krüger, I. Peeken, D. W. R. Wallace
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2014
• Subjects: Physics; QC1-999; Chemistry; QD1-999; North East Atlantic
• Online Access: https://doi.org/10.5194/acp-14-1255-2014; https://doaj.org/article/5d569cae241f405f802b4fb10457ba1d

Methyl iodide (CH 3 I), bromoform (CHBr 3 ) and dibromomethane (CH 2 Br 2 ), which are produced naturally in the oceans, take part in ozone chemistry both in the troposphere and the stratosphere. The significance of oceanic upwelling regions for emissions of these trace gases in the global context is still uncertain although they have been identified as important source regions. To better quantify the role of upwelling areas in current and future climate, this paper analyzes major factors that influenced halocarbon emissions from the tropical North East Atlantic including the Mauritanian upwelling during the DRIVE expedition. Diel and regional variability of oceanic and atmospheric CH 3 I, CHBr 3 and CH 2 Br 2 was determined along with biological and physical parameters at six 24 h-stations. Low oceanic concentrations of CH 3 I from 0.1–5.4 pmol L −1 were equally distributed throughout the investigation area. CHBr 3 and CH 2 Br 2 from 1.0 to 42.4 pmol L −1 and to 9.4 pmol L −1 , respectively were measured with maximum concentrations close to the Mauritanian coast. Atmospheric CH 3 I, CHBr 3 , and CH 2 Br 2 of up to 3.3, 8.9, and 3.1 ppt, respectively were detected above the upwelling, as well as up to 1.8, 12.8, and 2.2 ppt at the Cape Verdean coast. While diel variability in CH 3 I emissions could be mainly ascribed to oceanic non-biological production, no main driver was identified for its emissions over the entire study region. In contrast, biological parameters showed the greatest influence on the regional distribution of sea-to-air fluxes of bromocarbons. The diel impact of wind speed on bromocarbon emissions increased with decreasing distance to the coast. The height of the marine atmospheric boundary layer (MABL) influenced halocarbon emissions via its influence on atmospheric mixing ratios. Oceanic and atmospheric halocarbons correlated well in the study region, and in combination with high oceanic CH 3 I, CHBr 3 and CH 2 Br 2 concentrations, local hot spots of atmospheric halocarbons could solely be ...