Supplementary material to "Photochemistry of the sea-surface microlayer (SML) influenced by a phytoplankton bloom: A mesocosm study"

S1 Ferrioxalate actinometryThe ferrioxalate actinometer is among the most widely used system due to its strong absorption in the UV-Vis spectrum.When exposed to light, Fe(III) photochemically decomposed to form Fe (II), and this process can be quantified via complexation with 1,10-phenanthroline (Hatchard and Parker, 1956).The simplified reaction mechanisms for the photolysis of Fe (III) and the complexation of Fe (II) with 1,10 phenanthroline are:The potassium ferrioxalate solution was placed inside the photoreactor and the first aliquot (2 mL) was extracted before the irradiation with the same solar simulator used for the ambient seawater samples.After that, the Xe lamp was turned on and light-exposed aliquots (2 mL each) were collected every 20 seconds for 2 minutes.The time was accurately controlled using a timer.All this process took place under continuous stirring.Right after extraction, all the collected aliquots were put together in amber glass bottles with the previously prepared mixtures of ultra-pure water, sodium acetate, 1,10-phenanthroline hydrochloride monohydrate (Fluka) and sulphuric acid (96 %, Merck) to form the complex.The total volume of the complex was 10 mL.The volumes of each solution of the mixture were chosen so the measured absorbance of the complex at 510 nm was below 1.0.The amber glass bottles were covered with aluminium foil and stored in a dark shelf for 40 minutes to complete the complexation.After that, the absorbance of each sample at 510 nm was measured in high performance 10 x 10 mm quartz glass cuvette (Hellma) with a UV/VIS spectrometer (PerkinElmer Instruments).Data was acquired using the Lambda 900 software.The absorbance of the complexes for each light-exposure time was calculated from the average of two values Glyoxal 10075