Bromocarbons in the tropical coastal and open ocean atmosphere during the 2009 Prime Expedition Scientific Cruise (PESC-09)

Abstract

Atmospheric concentrations of very short-lived species (VSLS) bromocarbons, including CHBr_3, CH_2Br_2, CHCl_2Br, CHClBr_2, and CH_2BrCl, were measured in the Strait of Malacca and the South China and Sulu–Sulawesi seas during a two-month research cruise in June–July 2009. The highest bromocarbon concentrations were found in the Strait of Malacca, with smaller enhancements in coastal regions of northern Borneo. CHBr_3 was the most abundant bromocarbon, ranging from 5.2 pmol mol^−1 in the Strait of Malacca to 0.94 pmol mol^−1 over the open ocean. Other bromocarbons showed lower concentrations, in the range of 0.8–1.3 pmol mol^−1 for CH_2Br_2, 0.1–0.5 pmol mol^−1 for CHCl_2Br, and 0.1–0.4 pmol mol^−1 for CHClBr_2. There was no significant correlation between bromocarbons and in situ chlorophyll a, but positive correlations with both MODIS and SeaWiFS satellite chlorophyll a. Together, the short-lived bromocarbons contribute an average of 8.9 pmol mol^−1 (range 5.2–21.4 pmol mol^−1) to tropospheric bromine loading, which is similar to that found in previous studies from global sampling networks (Montzka et al., 2011). Statistical tests showed strong Spearman correlations between brominated compounds, suggesting a common source. Log–log plots of CHBr_3/CH_2Br_2 versus CHBr_2Cl/CH_2Br_2 show that both chemical reactions and dilution into the background atmosphere contribute to the composition of these halocarbons at each sampling point. We have used the correlation to make a crude estimate of the regional emissions of CHBr_3 and to derive a value of 32 Gg yr^−1 for the Southeast (SE) Asian region (10° N–20° S, 90–150° E). Finally, we note that satellite-derived chlorophyll a (chl a) products do not always agree well with in situ measurements, particularly in coastal regions of high turbidity, meaning that satellite chl a may not always be a good proxy for marine productivity.