Long-term Measurements of SO2 Concentrations Within the Atmospheric Column on Gozo (Maltese Islands)

Sulphur dioxide (SO¬2) concentrations were measured over a twelve-year period (2011 - 2023) at the Giordan Lighthouse Atmospheric Observatory, located on the Island of Gozo (forming part of the Maltese Archipelago), in the Central Mediterranean. Trend analysis reveals that SO2 concentrations are decreasing at an annual average rate of 0.03 ppbv per year. This is in keeping with what has been recorded throughout Europe following the introduction of several sulphur directives by the European Union and stringent regulations on marine fuels by the International Maritime Organisation. SO2 concentrations exhibit a strong seasonal variability of 55.9% with a maximum in July and a minimum in March, which contrasts with what is observed in Northern Europe. The diurnal amplitude of SO2 is 29.7% with a maximum at 10:00 and a minimum at 19:00. With respect to wind direction, SO2 concentrations exhibit a maximum when the prevailing wind in from the 0° - 60° sector due to emissions originating mainly from two sources, the active Etna volcano and ships traversing the Straits of Sicily. A broad minimum of circa 0.32 ppbv is observed when the wind is blowing from the 160° - 300° sector.