Investigation of reactive gases and methane variability in the coastal boundary layer of the central Mediterranean basin

We present a characterization of reactive gases (RG: O 3 , NO, NO 2 , SO 2 , CO) and methane (CH 4 ) variability in the central Mediterranean basin, analyzing in situ measurements at three new permanent WMO/GAW Observatories in Southern Italy: Capo Granitola – CGR (Sicily), Lamezia Terme – LMT (Calabria) and Lecce – ECO (Apulia). At all the measurement sites, a combination of the breeze wind system (especially at CGR and LMT), PBL dynamics, anthropogenic/natural emissions, and photochemistry lead the appearance of well-defined diurnal cycles for the observed RG. According to O 3 /NO x variability, local emissions appeared to influence CGR and LMT (no NO x data were available for ECO during the period of study) in 4% and 20% of the hourly data, nearby sources in 39% and 40%, remote sources in 31% and 14%, while background O 3 /NO x were observed in 26% of cases for both the stations. Most of the background O 3 /NO x were observed during daytime, when offshore air masses usually affected the measurement sites. Local sources of CH 4 at CGR can be related to biogenic (oxic) emissions from biomasses along the coastline, while emissions from live stocks can represent a local source of CH 4 at LMT. Finally, we provide first hints about the export of O 3 from Sicily/Southern Italy to the Mediterranean Sea by comparing simultaneous observations at CGR and Lampedusa (LMP), a small island in the middle of the Strait of Sicily where a WMO/GAW Regional Station is located. In summer, O 3 increased by some 7 ppb for transport times lower than 48 h, while no statistical significant differences were observed for travel time longer than 48. This would suggest that photochemical O 3 production occurred within air-mass travelling from CGR to LMP, but also that the central Mediterranean MBL represents a O 3 sink for relatively aged air-masses.