Wind and seasonal variabilities of concentrations of oxides of nitrogen, measured at Giordan Lighthouse Geosciences Observatory, Gozo (Maltese Archipelago)

Abstract

Concentrations of oxides of nitrogen (NOx), as the sum total of nitric oxide (NO) and nitrogen dioxide (NO2), the individual parts, i.e., NO and NO2, (NOx = NO + NO2), and wind speed and direction measurements were gathered over a thirteen-year period (2011–2023) at the Giordan Lighthouse Geosciences Observatory, located on the Island of Gozo, forming part of the Maltese Archipelago (Central Mediterranean). The atmospheric concentration measurements were recorded with a Thermo Scientific Model 42i NOx analyser, which employs the chemiluminescence technique to detect atmospheric traces of NOx concentrations. In this case study, an investigation was conducted to understand the wind and seasonal variabilities of the measured concentrations. The highest NOx concentrations occurred when the prevailing wind originated from the SE, while a broad minimum was observed when the wind blew from the S–W sector. The maxima were primarily associated with land-based sources, predominantly vehicular emissions on the main island, i.e., Malta. The amplitudes for NO, NO2, and NOx in relation to wind direction were 63%, 125%, and 121%, respectively. Significant variabilities were observed during the autumn season. Regarding wind speed, the NOx concentrations reached their peak during high-wind-speed events, which are associated with transboundary pollution. A secondary broad maximum was observed for wind forces between 2 and 4, while the lowest concentrations were recorded at wind force 9. The NOx concentrations exhibited a seasonal maximum in spring and a minimum in winter, which contrasts with the findings from the Monte Cimone station in Italy. The seasonal amplitudes for NO, NO2, and NOx were 46%, 15%, and 17%, respectively. It is evident that NO concentrations exhibited a greater seasonal variability, whereas NO2 concentrations demonstrated significant variability in relation to wind direction.