Analysis and Observations Concerning Concentrations of Nitrogen Oxides at the Giordan Lighthouse Atmospheric Observatory, Gozo (Maltese Islands)

Measurements of concentrations of nitrogen oxides (NOx) were collected over a period of thirteen years (2011–2023). The data were collected at Giordan Lighthouse atmospheric monitoring and research station on the Island of Gozo, forming part of the Maltese Archipelago, in the Central Mediterranean. Trend analysis shows that NOx concentrations are decreasing at an annual rate of 0.15 ppbv per year. This is in comparison to what has been recorded across Europe due to stricter regulations and improvements in vehicle technologies. Significant reductions were observed during the COVID-19 pandemic due to the implementation of lockdowns and restrictions on mobility. NOx concentrations also exhibit an amplitude seasonal variability of 35% with a maximum in October and a minimum in December, while the nitric oxide (NO) component of NOx presents a broad maximum in May/June and a minimum in February. NOx concentrations also show a strong diurnal variability with a maximum in the morning and a minimum in the afternoon. The diurnal amplitude of NOx and NO is 44% and 148%, respectively. With respect to wind direction, the NOx concentrations exhibit a maximum when the prevailing wind is from the South-East sector and a minimum when the wind is blowing from the West sector.