Analysis of Nitric Oxide and Nitrogen Dioxide Variability at a Central Mediterranean WMO/GAW Station

The World Meteorological Organization / Global Atmosphere Watch (WMO/GAW) observation site of Lamezia Terme (code: LMT) in Calabria, Italy has been measuring nitric oxide (NO) and nitrogen dioxide (NO2) (together referred to as NOx) for a decade, however only a limited number of studies have evaluated their variability at the site, accounting for short measurement periods. In this work, nine continuous years (2015-2023) of measurements are analyzed to assess daily, weekly, seasonal and multi-year tendencies, also accounting for local wind circulation, which is known to have a relevant impact on LMT’s measurements due to the station’s coastal characteristics in the context of the central Mediterranean Basin. For the first time, a multi-year evaluation on LMT data also considers the local vertical wind profile record to integrate conventional measurements with additional information on air mass transport at low altitudes. The analysis showed peaks in early morning NOx concentrations attributable to rush hour traffic, while in the evening NO2 peaks are present with minor NO counterparts. Weekly cycles have yielded the most statistically significant results of any other similar evaluation at the sites, with all combinations of parameters, seasons, and wind corridors indicating tangible differences between weekday (Monday to Friday) and weekend (Saturday and Sunday) concentrations. The analysis of multi-year variability has shown a slightly declining tendency, however sporadic bursts in concentrations limit the statistical significance of downward trends.