Rapid, localized loss of ozone is predicted to occur in the mid-latitude and tropical stratosphere in the presence of very large concentrations of sulfate aerosols. Volcanic eruptions can increase the effective surface area of sulfuric acid so that heterogeneous reactions involving ClONO₂, and secondarily N₂O₅, are able to suppress NO_x abundances by more than a factor of 10 relative to gas phase chemistry. When NO_x levels fall below a threshold, e.g., 0.6 ppb at 24 km in mid-latitudes, the chlorine-catalyzed loss of O₃proceeds at rates comparable to those during the formation of the Antarctic ozone hole, more than 50 ppb per day. If such losses occurred following the eruption of Mount Pinatubo in the most volcanically perturbed regions over the tropics and mid-latitudes, this model predicts that they are driven primarily by the suppression Of NO_x below these critical levels. The increase in stratospheric chlorine since El Chichon has made Mount Pinatubo more than twice as effective in causing rapid O₃ loss. Overall global losses associated with a volcanic eruption are approximately linear in the amount of sulfate surface area, but depend critically on the rate of the CIONO₂-sulfate reaction.

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 CFCl3represents 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.

Methyl bromide (CH₃Br) supplies about half of the chemically active bromine (Br_y) in the stratosphere. Efforts to control Br_y-catalyzed ozone depletion by phasing out, for example, agricultural use of CH₃Br may be thwarted by a lack of understanding of how the varied biogeochemical processes interact as a coupled system: in addition to the chemical industry, large natural sources come from the ocean; and losses occur in the atmosphere, ocean, and soils. A simplified one-dimensional stratosphere-troposphere-ocean model for {CH³Br, Br_y} that fits current understanding of sources and sinks is analyzed in terms of natural modes. Surface and ocean sources have effectively different steady state lifetimes (1.0 and 0.5 years, respectively), but the natural-mode decay times of the system (1.8 years for CH₃Br and 4.5 years for stratospheric Br_y) do not depend on the location of sources. The cumulative ozone depletion resulting from a single atmospheric release of CH₃Br integrates over the consequent slow rise and fall of Br_y in the lower stratosphere. Thus, in spite of the 1-year lifetime of CH₃Br, only half of the anticipated ozone recovery occurs in the first 7 years.