European sources of halocarbons and nitrous oxide: Update 1986

Semi-continuous measurements of CFCl₃, CF₂Cl₂, CCl₄, CH₃CCl₃ and N₂O were made at Adrigole, Ireland as part of the Atmospheric Lifetime Experiment (ALE). Clean, baseline air from the Atlantic Ocean was measured approximately 70% of the time; pollution events from Europe, for the remainder. The two final years of ALE data from Adrogole give a five-year record from July 1978 to June 1983. This paper extends previous work on the relative enhancements of trace gases during pollution episodes and presents (1) unambiguous identification of elevated levels of N₂O concurrent with halocarbon pollution events, (2) detection of trends in emission of CH₃CCl₃, (3) discovery of seasonal variations in emission of CF₂Cl₂, CCl₄ and CH₃CCl₃, (4) characterization of typical summer and winter pollution episodes, and (5) identification of weather patterns over Europe that are associated with high concentrations of CFCs at Adrigole. Some of these results assume that CFCl₃ represents a uniform, well buffered source from the continent. The latter two results are particularly useful in the testing and calibration of three-dimensional chemical transport models. Observed enhancements are marginally consistent with estimates of halocarbon use by the chemical industry. The source of nitrous oxide correlated with halocarbons is 0.8 Tg(N)/yr from Europe alone and represents approximately 10% of the global stratospheric loss.