HIGH FREQUENCY MEASUREMENTS OF DIBROMOMETHANE IN THE ATMOSPHERE AND NEW FINDINGS ON ITS OCEANIC SOURCES
Dibromomethane (CH2Br2) is mostly emitted from the ocean, and is believed to be involved in the stratospheric ozone chemistry. Hourly measurements of this compound were done as a part of the NIES halocarbon monitoring project at Hateruma Island (24.05N, 123.8E) and Cape Ochiishi (43.15N, 145.5E). The former is a coral island in subtropical ocean, and the latter is a cliff cape facing into the north-west Pacific Ocean with rich macro-algae growth. CH2Br2 from Hateruma (2004~2011) showed a prominent seasonal variation, lower in summer (~0.9ppt) than in winter (~1.3 ppt), which could be explained by its enhanced removal by OH radicals in summertime. On the other hand, CH2Br2 from Ochiishi (2008~2011) was highly variable often exceeding 2 ppt in summertime with minimum baseline mixing ratios close to those from Hateruma, and was almost constant around 1.3ppt in winter. These findings suggest (1) the macroalgal emission of CH2Br2 was rather limited to summertime, whereas (2) the open ocean source of CH2Br2, which would outweigh its coastal algal source, was likely to have fairly constant strength throughout the year.
Yokouchi, Y., National Institute for Environmental Studies, Japan, email@example.com
Saito, T., National Institute for Environmental Studies, Japan
Mukai, H., National Institute for Environmental Studies, Japan
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