Quantification of sulfur compound emissions from Sargassum Strandings

Massive strandings of pelagic Sargassum release large quantities of hydrogen sulfide (H₂S), sulfur dioxide (SO₂), and dimethyl sulfide (DMS), posing risks to human health and local air quality. Emission factors needed to model and mitigate impacts are currently lacking. This study quantified sulfur emission factors from decomposing sargassum under laboratory conditions. Sargassum and seawater were collected from Key Biscayne, Florida, during summer and winter to investigate seasonal variability and the influence of seawater. Decomposition was monitored in sealed chambers over 14 days, measuring daily total sulfur, H₂S, and SO₂ using a UV fluorescence analyzer. DMS was analyzed by gas chromatography-mass spectroscopy (GC-MS). Sulfur emissions peaked within two days of decomposition before gradually declining. Seasonal variation was observed in emission rates, with summer samples exhibiting higher emission rates (average total sulfur peak: 3440 μg/kg-day in summer samples) compared to winter samples (71.2 μg/kg-day). The presence of seawater enhanced sulfur emissions across seasons. The highest total sulfur emission factor was observed in the "summer with seawater" condition, peaking at approximately 5190 μg/kg-day. H₂S was the dominant sulfur species (29% on average). DMS was the major volatile organic compounds. These findings demonstrate that seasonal factors and environmental conditions are key determinants of sargassum sulfur emissions. The quantified emission factors can inform public health management strategies, highlighting the need for rapid removal of water-saturated sargassum, particularly during summer, to mitigate H₂S release. The detection of DMS and SO₂ indicates that sargassum strandings are a significant coastal source of aerosol precursors, impacting atmospheric chemistry.