Tropospheric halocompounds and nitrous oxide monitored at a remote site in the Mediterranean

Analysis of time series and trends of nitrous oxide (N2O) and halocompounds weekly monitored at the Mediterranean island of Lampedusa are discussed. Atmospheric N2O levels showed a linear upward growth rate of 0.78 ppb yr−1 and mixing ratios comparable with Northern Hemisphere global stations. CFC-11 and CFC-12 time series displayed a decline consistent with their phase-out. Chlorofluorocarbons (CFCs) replacing compounds and SF6 exhibited an increasing temporal behaviour. The most rapid growth rate was recorded for HFC-134a with a value of 9.6% yr−1. The industrial solvents CCl4 and CH3CCl3, banned by the Montreal Protocol, showed opposite trends. While CH3CCl3 reported an expected decay of −1.8 ppt yr−1, an increasing rate of 5.7 ppt yr−1 was recorded for CCl4 and it is probably related to its relatively long lifetime and persisting emissions. Chlorinated halomethanes showed seasonality with a maximum in early April and a minimum at the end of September. Halon-1301 and Halon-1211 displayed a decreasing trend consistent with industry emission estimates.An interspecies correlation analysis gave positive high correlations between HCFC-22 and HFC-134a (+0.84) highlighting the common extensive employment as refrigerants. Sharing sources inferred the high coupling between CH3Cl and CH3Br (+0.73) and between CHCl3 and CH2Cl2 (+0.77). A singular strong relationship (+0.55) between HFC-134a and CH3I suggested the influence of an unknown anthropogenic source of CH3I.Constraining of source and sink distribution was carried out by transport studies. Results were compared with the European Environment Agency (EEA) emission database. In contrast with the emission database results, our back trajectory analysis highlighted the release of large amounts of HFC-134a and SF6 from Eastern Europe. Observations also showed that African SF6 emissions may be considerable. Leakages from SF6 insulated electrical equipments located in the industrialized Northern African areas justify our observations.