Investigation of Carbon Monoxide, Carbon Dioxide, and Methane Source Variability at the WMO/GAW Station of Lamezia Terme (Calabria, Southern Italy) Using the Ratio of Ozone to Nitrogen Oxides as a Proximity Indicator

In the field of Atmospheric Sciences, source apportionment and a more detailed understanding of local and remote contributions to observed concentrations of greenhouse gases (GHGs) across international networks, such as the World Meteorological Organization—Global Atmosphere Watch (WMO/GAW), can be achieved via the implementation of new atmospheric tracers. One tool for achieving a more precise understanding of GHG emissions is the evaluation of air mass aging indicators, which can serve as proximity indicators. In this study, the ratio between ozone (O3) and nitrogen oxides (NOx) is applied to nine continuous years (2015–2023) of measurements at the Lamezia Terme (LMT) observation site in Calabria, Southern Italy, to differentiate the aging of air masses and identify four distinct categories: LOC (local), N–SRC (near source), R–SRC (remote source), and BKG (atmospheric background). Due to possible overestimation of nitrogen dioxide (NO2) caused by heated (~300–400 °C) molybdenum converters used in the employed instruments, a correction factor based on a previous study has been integrated to further analyze the results. Additionally, this work introduces a second correction factor based on the local behavior of surface ozone and the diurnal peaks observed during boreal warm seasons in an area characterized by a Mediterranean climate. The results of this study confirm the hypotheses of previous works on local sources of pollution: the LOC category yields the highest concentrations observed at the site, which are in accordance with the northeastern wind sector and anthropogenic sources. R–SRC and BKG are more representative of atmospheric background levels and characterize westerly winds from the Tyrrhenian Sea. N–SRC, as expected, shows an intermediate behavior between local and remote/background levels. Differences in results between standard O3/NOx categories and corrected measurements will need to be investigated in future studies.