Macroalgae (seaweeds) are a major contributor in emitting very short-lived (VSL) bromocarbons into the atmosphere especially in tropical countries with high primary productivity such as Malaysia. Abiotic factors such as light intensities and chlorophyll a concentrations can influence the production of bromocarbons emitted by seaweeds, however, not many studies have systematically quantified their influence on the release rates of VSL bromocarbons. Hence, to measure this, we used a seaweed

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... e system mimicking a natural environment to study the release rate of VSL bromocarbons (CH 2 Br 2 , CHBr 3 and CHBr 2 Cl) for several red, brown and green seaweeds (Gracilaria changii, Ulva reticulata, Caulerpa racemosa var. macrophysa, Kappaphycus alvarezii, Sargassum binderi, Sargassum siliquosum, and Padina australis. The production of VSL bromocarbons showed a diurnal cycle with halocarbon concentrations increasing to a maximum level at mid-day (1738 pmolL -1 ) and decreasing when light intensity and SST decreased. The production of VSL bromocarbons of seaweeds kept in the sunlight is five times higher than the production of aquaculture tanks placed in dark environments indicating the occurrence of photochemical production. The average photochemical rate for VSL bromocarbons from aquaculture tank experiments ranges from 1 to 137 pmol per g -1 FW -1 h -1 . This makes the red seaweeds (Gracilaria changii) as the highest. Likewise, bromoperoxide (BPO) extracted from all seaweeds also showed the highest activity in red seaweed followed by brown and green seaweed.