Abstract. Bromoform is the major by-product from chlorination of cooling water in coastal power plants. Power plants in East and Southeast Asian economies have increased rapidly exceeding global growth. Bottom-up estimates of bromoform emissions based on few measurements appear to under-represent the industrial sources of bromoform from East Asia. By means of Lagrangian analyses, we assess the amount of bromoform produced from power plant cooling water treatment in East and Southeast Asia. The spread of bromoform is simulated as passive particles that are advected using the 3-dimensional velocity fields from the high-resolution NEMO-ORCA0083 ocean general circulation model. Simulations are run for three scenarios with varying initial bromoform concentrations given by the range of measurements of bromoform in cooling water discharge. From comparison of our model results to observations, we expect initial bromoform concentrations between 20–60 µg L−1 used for the two lower scenarios, to be most realistic. From these two scenarios, we find elevated bromoform along the coastlines of East Asia with average concentrations of 23 and 68 pmol L−1 and maximum values in the Yellow, Japan and East China Seas. The industrially-produced bromoform is quickly emitted into the atmosphere with average air-sea flux of 3.1 and 9.1 nmol m−2 h−1, respectively. Based on the emission estimates, atmospheric abundances of anthropogenic bromoform are derived from FLEXPART simulations and compared to simulations based on climatological bottom-up emission estimates. In the marine boundary layer of East Asia, anthropogenic bromoform amounts up to 0.5–1.6 ppt during boreal summer and is thus 2–7 times larger compared to the bottom-up estimates. During boreal winter some part of the anthropogenic bromoform is transported by the northeasterly winter monsoon towards the tropical regions, whereas during boreal summer anthropogenic bromoform is confined to the northern hemisphere subtropics. Convective events in the tropics entrain an additional 0.03 ppt of anthropogenic bromoform into the upper troposphere/lower stratosphere. We find that bromoform from cooling water treatment in East Asia is a significant source of atmospheric bromine responsible for annual emissions of 100–300 Mmol Br, which might be a missing factor in global flux estimates of organic bromine. About 90 % of this anthropogenic bromoform is discharged north of 20° N, while in the tropics natural sources dominate and only a small fraction of the anthropogenic bromoform reaches the stratosphere.;
