Continuous observations of CO2 and CH4 in Italy by permanent observatories

The Mediterranean basin is considered a global hot-spot region for climate change and air-quality. CO₂ and CH₄ are the single most important anthropogenic greenhouse gases (GHG) in the atmosphere. Fossil fuel emissions are the main driver of the increasing atmospheric CO₂ mixing ratios in the global atmosphere, while other anthropogenic sources (e.g., ruminants, rice agriculture, fossil fuel exploitation, landfills and biomass burning) strongly determine trends for CH₄.

In this work, we analysed a set of continuous long-term measurements of CO₂ and CH₄ carried out at 5 atmospheric observatories in Italy from 2015 and spanning from the Alpine region to central Mediterranean Sea: Plateau Rosa (western Italian Alps, 3480 m a.s.l.), Mt. Cimone (northern Apennines, 2165 m a.s.l.), Lamezia Terme (Calabria region, coastline), Capo Granitola (southern Sicily coastline) and Lampedusa Island. Mt. Cimone is also a "class-2" ICOS-RI station, while Plateau Rosa and Lampedusa are in the labelling process. Starting time of GHG observations ranged from 1979 for Mt. Cimone to 2015 for Capo Granitola. Due to their different locations and ecosystems, they provide useful hints to investigate CO₂ and CH₄ variability on different latitudinal and altitudinal ranges in the Mediterranean basin and to study natural and anthropogenic-related processes able to affect the observed variability. The study addresses primarily differences in daily and seasonal cycles at the different sites, and implemented procedures to identify background conditions. Marked differences among the daily cycles at the various sites exist. Consequently, different data selection methods need to be adopted to isolate background conditions. The effect of the data selection on the seasonal cycle and long-term evolution is investigated. Moreover, the availability of 2 co-located measurement laboratories at Mt. Cimone (the ICOS "class-2" station managed by CNR and the WMO/GAW observatory managed by the Italian Air Force) provides the opportunity to systematically evaluate the impact of different calibration and data flagging strategies, as well as different sampling methodologies to CO₂ and CH₄ atmospheric observations.