Particulate methanesulfonic acid over the central Mediterranean Sea: Source region identification and relationship with phytoplankton activity

Many efforts have been dedicated toward understanding the role of biogenic sulfur particles as a climate regulator. Herein, we investigate the relationship between the atmospheric concentration of methanesulfonic acid (MSA) and phytoplankton biomass in the Mediterranean Sea by identifying the main MSA source regions during a springtime intensive observation period. The study approach combines i) spatio-temporal correlation analysis between in situ aerosol data measured in April 2016 at Capo Granitola (southern Sicily), and high-resolution ocean color composites, ii) back-trajectory analysis, and iii) potential source contribution function (PSCF) algorithm. The southwestern Mediterranean region (between Sardinia and the Algerian coast) was identified as the most probable dimethylsulfide (DMS) source region contributing to the observed MSA concentrations. Conversely, the blooming northwestern Mediterranean Sea region did not appear to contribute significantly. The present analysis shows that the reasons may be biotic (phytoplankton type, stress level) or abiotic (sea surface temperature), or a combination of both. We also postulate that the identified source region is associated with the production of non-sea-salt-sulfate and secondary organic aerosols from the processing of sea-released volatile organic compounds.