Abstract
Abstract. Bromoform is the major by-product from chlorination of cooling water in coastal power plants. The number of power plants in East and Southeast Asian economies has increased rapidly, exceeding mean global growth. Bottom-up estimates of bromoform emissions based on few measurements appear to under-represent the industrial sources of bromoform from East Asia. Using oceanic 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 three-dimensional velocity fields over the years 2005/2006 from the high-resolution NEMO-ORCA0083 ocean general circulation model. Simulations are run for three scenarios with varying initial bromoform concentrations based on the range of bromoform measurements in cooling-water discharge. Comparing the modelled anthropogenic bromoform to in situ observations in the surface ocean and atmosphere, the two lower scenarios show the best agreement, suggesting initial bromoform concentrations in cooling water to be around 20–60 µg L−1. Based on these two scenarios, the model produces elevated bromoform in coastal waters of East Asia with average concentrations of 23 and 68 pmol L−1 and maximum values in the Yellow Sea, Sea of Japan and East China Sea. The industrially produced bromoform is quickly emitted into the atmosphere with average air–sea flux of 3.1 and 9.1 nmolm-2h-1, respectively. Atmospheric abundances of anthropogenic bromoform are derived from simulations with the Lagrangian particle dispersion model FLEXPART based on ERA-Interim wind fields in 2016. In the marine boundary layer of East Asia, the FLEXPART simulations show mean anthropogenic bromoform mixing ratios of 0.4–1.3 ppt, which are 2–6 times larger compared to the climatological bromoform estimate. During boreal winter, the simulations show that 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 0.04–0.05 ppt of anthropogenic bromoform into the stratosphere, averaged over tropical Southeast Asia. In our simulations, only about 10 % of anthropogenic bromoform is outgassed from power plants located in the tropics south of 20∘ N, so that only a small fraction of the anthropogenic bromoform reaches the stratosphere. We conclude that bromoform from cooling-water treatment in East Asia is a significant source of atmospheric bromine and might be responsible for annual emissions of 100–300 Mmol of Br in this region. These anthropogenic bromoform sources from industrial water treatment might be a missing factor in global flux estimates of organic bromine. While the current emissions of industrial bromoform provide a significant contribution to regional tropospheric budgets, they provide only a minor contribution to the stratospheric bromine budget of 0.24–0.30 ppt of Br.
Highlights
Power plants require cooling water to regulate the temperature in the system
Average values of 6–13 pmol L−1 were measured in the Yellow and East China seas during boreal spring and summer (Yang et al, 2014, 2015), and 17 pmol L−1 was measured in boreal winter (He et al, 2013b)
Our analyses suggests that anthropogenic bromoform accumulates in the boundary layer, increasing the bromine budget in East and Southeast Asia by 85 %–254 % compared to the Ziska2013 climatology
Summary
Power plants require cooling water to regulate the temperature in the system. As their demand for cooling water is very high, power plants are often located at the coast to profit from an unlimited water supply. The composition and amount of generated DBPs depend on many factors including the type and concentration of the injected oxidant and the chemical characteristics of the treated water such as salinity, temperature and amount of dissolved organic matter (Liu et al, 2015). Cooling-water effluents regularly involve the discharge of large water volumes into the marine environment (Khalanski and Jenner, 2012). This water is often warmer than the surrounding waters, and its decreased density means it stays at the sea surface. Chemicals such as DBPs contained in cooling water are likely to spread laterally across the sea surface, which facilitates air– sea gas exchange for volatile DBPs
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