Dibromomethane (CH2Br2), a natural stratospheric ozone depleting substance, is mostly emitted from the ocean, but the relative importance of coastal (or macroalgae) and open ocean emissions is unknown. We made long-term high-frequency measurements of CH2Br2 concentrations at two remote coastal sites in Japan, on the subtropical Hateruma Island (poor in macroalgae) and at Cape Ochiishi (rich in macroalgae). CH2Br2 concentrations at Hateruma showed prominent seasonal variation, being lower in summer (around 0.94 ppt) than in winter (around 1.23 ppt). In contrast, CH2Br2 concentrations at Ochiishi were highly variable, often exceeding 2 ppt in the summer but with minimum baseline concentrations close to those from Hateruma; in the winter the concentrations were almost constant at about 1.3 ppt. Analysis of the data suggested that (1) emissions from macroalgae were not likely to extend offshore, but instead were localized near the shore, (2) strong macroalgal emissions of CH2Br2 were almost limited to the summer, but it was not reflected in the seasonality of the baseline concentrations of CH2Br2 in the atmosphere, and therefore (3) macroalgal or coastal emissions of CH2Br2 in the temperate zone might have a rather limited contribution to the global CH2Br2 sources. These findings are especially important for the understanding of the tropospheric and stratospheric bromine budget.

中文翻译：

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在富含藻类和缺乏藻类的沿海地区大气中二溴甲烷的长期高频测量

二溴甲烷 (CH2Br2) 是一种天然的平流层臭氧消耗物质，主要从海洋排放，但沿海（或大型藻类）和公海排放的相对重要性尚不清楚。我们在日本的两个偏远沿海地点，即亚热带的波照间岛（缺乏大型藻类）和落石角（富含大型藻类），对 CH2Br2 浓度进行了长期高频测量。波照间的 CH2Br2 浓度表现出明显的季节性变化，夏季（约 0.94 ppt）低于冬季（约 1.23 ppt）。相比之下，Ochiishi 的 CH2Br2 浓度变化很大，通常在夏季超过 2 ppt，但最低基线浓度接近 Hateruma 的浓度；在冬季，浓度几乎恒定在 1.3 ppt 左右。数据分析表明：（1）大型藻类的排放不太可能向近海延伸，而是集中在海岸附近，（2）CH2Br2 的强烈大型藻类排放几乎仅限于夏季，但没有体现在季节性上大气中 CH2Br2 的基线浓度，因此 (3) 温带的大型藻类或沿海 CH2Br2 排放可能对全球 CH2Br2 源的贡献相当有限。这些发现对于了解对流层和平流层溴收支尤为重要。但它并未反映在大气中 CH2Br2 基线浓度的季节性中，因此 (3) 温带的大型藻类或沿海 CH2Br2 排放对全球 CH2Br2 源的贡献可能相当有限。这些发现对于了解对流层和平流层溴收支尤为重要。但它并未反映在大气中 CH2Br2 基线浓度的季节性中，因此 (3) 温带的大型藻类或沿海 CH2Br2 排放对全球 CH2Br2 源的贡献可能相当有限。这些发现对于了解对流层和平流层溴收支尤为重要。