Supplementary material to "Uncovering precursors for VOC production from ozonolysis of seawater"

Methods Seawater samplingSurface seawater was routinely collected from the Western Channel Observatory station L4 using the rosette on the RV Plymouth Quest at a mean depth of 1.8 ± 0.3 m (range: 1.4 m) between 08:00-10:00 local time.Seawater was transferred directly from Niskin bottles into acid-washed, thoroughly 15 rinsed glass bottles using Tygon tubing and gas-sensitive techniques.Bottles were allowed to overflow 3× before sealing with a ground-glass stopper, minimizing bubbles and gas loss.Samples were transported to the laboratory in a dark, insulated cool box and analysed as soon as possible to limit DOM alteration (59% within 3 h, 94% within 24 h). Sampling campaigns covered contrasting seasons: 20