Simulations of anthropogenic bromoform indicate high emissions at the coast of East Asia

Abstract

<p><strong>Abstract.</strong> 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<sup>−1</sup> 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<sup>−1</sup> 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<sup>−2</sup> h<sup>−1</sup>, 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.</p>

Renewed and emerging concerns over the production and emission of ozone-depleting substances

“…For instance, in coastal areas where these cooling waters are dumped, bromoform concentrations range between 0.5 and 50 µg L -1 (REFS 81,82 ). For South-East Asia alone, anthropogenic emissions are on average 24 Gg Br yr −1 (REF 83 ), which is 30% more than the measurement-based estimate of total emission derived for the same region (18 Gg Br yr −1 ; from REF 74 , Fig. 4).…”

Atmospheric gas-phase composition over the Indian Ocean

“…CH2Br2 from the sea to the atmosphere (Mehlmann et al, 2020). Enhanced emissions of brominated VSLS coincide with biologically active equatorial and coastal upwelling regions (Quack et al, 2007) and the distribution of macroalgae and anthropogenic sources along the coasts (Carpenter and Liss, 2000;Maas et al, 2020). Iodinated VSLS such as CH3I, on the other hand, show elevated oceanic abundances in the subtropical gyre regions in agreement with identified production by photochemical reactions (Richter and Wallace, 2004).…”

“…Intraseasonal variability can impact atmospheric transport patterns over the Indian Ocean with the dominant mode being the eastward propagating Madden-Julian Oscillation (MJO). Equatorially trapped, baroclinic oscillations in the tropical wind field propagate slowly eastward across the Indian Ocean, Maritime Continent, and West Pacific with an intraseasonal cycle of 30-60 days (Madden and Julian, 1972). A typical MJO event exhibits large-scale convection anomalies where enhanced convection and rainfall develop over the western Indian Ocean with suppressed convection further east over the western Pacific (Zhang, 2005).…”

“…The atmospheric deposition of ozone on marine surface water and subsequent reaction with dissolved organic matter can also form volatile organoiodine compounds (Martino et al, 2009) or organobromine compounds (Kornmüller, 2007). Especially in polluted coastal regions, their formation from this process is expected in addition to the release of organohalogens formed during industrial disinfection processes (Maas et al, 2020). Measurement-based modelling showed that an unexpected formation of ozone from reactive bromine and iodine species can occur in the marine boundary layer near coastlines and ship plumes under VOC-limited conditions associated with high nitrogen oxide concentrations (Shechner and Tas, 2017).…”