Analysis of Urban-Level Greenhouse Gas and Aerosol Variability at a Southern Italian WMO/GAW Observation Site: New Insights from Air Mass Aging Indicators Applied to Nine Years of Continuous Measurements

Gaseous pollutants and aerosols resulting from anthropic activities and natural phenomena require adequate source apportionment methodologies to be fully assessed. Furthermore, it is crucial to differentiate between fresh anthropogenic emissions and the atmospheric background. The proximity method based on the O3/NOx (ozone to nitrogen oxides) ratio has been used at the Lamezia Terme (code: LMT) World Meteorological Organization—Global Atmosphere Watch (WMO/GAW) regional station in Italy to determine the variability of CO (carbon monoxide), CO2 (carbon dioxide), CH4 (methane), SO2 (sulfur dioxide), and eBC (equivalent black carbon), thus allowing the differentiation between local and remote sources of emission. Prior to this work, all O3/NOx ratios lower than 10 were grouped under the LOC (local) proximity category, thus including very low ratios (≤1), which are generally attributed by the literature to “urban” air masses, particularly enriched in anthropogenic emissions. This study, aimed at nine continuous years of measurements (2015–2023), introduces the URB category in the assessment of CO, CO2, CH4, SO2, and eBC variability at the LMT site, highlighting patterns and peaks in concentrations that were previously neglected. The daily cycle, which is locally influenced by wind circulation and Planetary Boundary Layer (PBL) dynamics, is particularly susceptible to urban-scale emissions and its analysis has allowed the highlighting of notable peaks in concentrations that were previously neglected. Correlations with wind corridors and speeds indicate that most evaluated parameters are linked to northeastern winds at LMT and wind speeds under 5.5 m/s. Weekly cycle analyses, i.e., differences between weekdays (MON-FRI) and weekends (SAT-SUN), have also highlighted tendencies driven by seasonality and wind corridors. The results highlight the potential of the URB category as a tool necessary to access a given area’s anthropogenic output and its impact on air quality and the environment.