Biogenic sulphate generation in the Mediterranean Sea and its contribution to the sulphate anomaly in the aerosol over Israel and the Eastern Mediterranean

Anomalous high sulphate levels during summer in the atmosphere over Israel and the Eastern Mediterranean sea have recently been reported. The usual explanation for this phenomenon has been long-range transport of sulphates emanating from industrial areas of eastern and central Europe. However, another possible source of the anomaly is marine biogenic production of sulphate from the oxidation of dimethylsulphide. Aerosols and gases were sampled on land, sea and air in central and northern Israel and analysed to determine inorganic ions, dimethylsulphide (DMS) and methanesulphonic acid (MSA). The results show that there is a definite, biogenic generation of sulphate from the Mediterranean sea and that this contributes to the sulphate content of the aerosol over Israel during the summer season. Using MSA as a tracer for DMS-derived sulphate, an attempt is made to assess the amount of this contribution. Based on MSA determinations and various reasonable assumptions about the behaviour of DMS, the biogenic contribution to the atmosphere is calculated to be between 6 and 22% (mean=11%) of the non-sea salt sulphate. These figures are supported by alternative calculations based on DMS data from independent sources. Lake Kinneret is possibly an additional minor source of atmospheric DMS in the region.