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

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Wisher, A., Oram, D. E., Laube, J. C., Mills, G. P., van Velthoven, P., Zahn, A., Brenninkmeijer, C. A. M.
• Format: Other/Unknown Material
• Language: English
• Published: 2018
• Subjects: North Atlantic
• Online Access: https://doi.org/10.5194/acp-14-3557-2014; https://www.atmos-chem-phys.net/14/3557/2014/

Short-lived organic brominated compounds make up a significant part of the organic bromine budget in the atmosphere. Emissions of these compounds are highly variable and there are limited measurements, particularly in the extra-tropical upper troposphere/lower stratosphere and tropical troposphere. Measurements of five very short-lived bromomethanes (VSLB) were made in air samples collected on the CARIBIC project aircraft over three flight routes; Germany to Venezuela/Columbia during 2009–2011, Germany to South Africa during 2010 and 2011 and Germany to Thailand/Kuala Lumpur, Malaysia during 2012 and 2013. In the tropical troposphere, as the most important entrance region to the stratosphere, we observe a total mean organic bromine derived from these compounds across all flights at 10–12 km altitude of 3.4 ± 1.5 ppt. Individual mean tropical tropospheric mixing ratios across all flights were 0.43, 0.74, 0.14, 0.23 and 0.11 ppt for CHBr 3 , CH 2 Br 2 , CHBr 2 Cl, CHBrCl 2 and CH 2 BrCl respectively. The highest levels of VSLB-derived bromine (4.20 ± 0.56 ppt) were observed in flights between Bangkok and Kuala Lumpur indicating that the South China Sea is an important source region for these compounds. Across all routes, CHBr 3 and CH 2 Br 2 accounted for 34% (4.7–71) and 48% (14–73) respectively of total bromine derived from the analysed VSLB in the tropical mid-upper troposphere totalling 82% (54–89). In samples collected between Germany and Venezuela/Columbia, we find decreasing mean mixing ratios with increasing potential temperature in the extra-tropics. Tropical mean mixing ratios are higher than extra-tropical values between 340–350 K indicating that rapid uplift is important in determining mixing ratios in the lower tropical tropopause layer in the West Atlantic tropics. O 3 was used as a tracer for stratospherically influenced air and we detect rapidly decreasing mixing ratios for all VSLB above ∼100 ppb O 3 corresponding to the extra-tropical tropopause layer.