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. For the first time, a multi-year evaluation of LMT data also considers the local wind lidar record to integrate conventional measurements with additional information on the transport of NOx at low altitudes. The study also considers data on local tourism and vehicular traffic to assess correlations with LMT’s measurements, thus providing new insights on NOx variability at the site. 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 (WD, Monday to Friday) and weekend (WE, 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.