Rapid ozone depletion after humidification of the stratosphere by the Hunga Tonga Eruption.

The eruption of the Hunga Tonga-Hunga Ha'apai volcano on 15 January 2022 offered a good opportunity to explore the early impacts of tropical volcanic eruptions on stratospheric composition. Balloon-borne observations near Réunion Island revealed the unprecedented amount of water vapor injected by the volcano. The enhanced stratospheric humidity, radiative cooling, and expanded aerosol surface area in the volcanic plume created the ideal conditions for swift ozone depletion of 5% in the tropical stratosphere in just 1 week. The decrease in hydrogen chloride by 0.4 parts per million by volume (ppbv) and the increase in chlorine monoxide by 0.4 ppbv provided compelling evidence for chlorine activation within the volcanic plume. This study enhances our understanding of the effect of this unusual volcanic eruption on stratospheric chemistry and provides insights into possible chemistry changes that may occur in a changing climate.

Measuring and modeling the lifetime of nitrous oxide including its variability.

Nitrous oxide lifetime is computed empirically from MLS satellite dataEmpirical N2O lifetimes compared with models including interannual variabilityResults improve values for present anthropogenic and preindustrial emissions.

Unprecedented Arctic ozone loss in 2011.

Chemical ozone destruction occurs over both polar regions in local winter-spring. In the Antarctic, essentially complete removal of lower-stratospheric ozone currently results in an ozone hole every year, whereas in the Arctic, ozone loss is highly variable and has until now been much more limited. Here we demonstrate that chemical ozone destruction over the Arctic in early 2011 was--for the first time in the observational record--comparable to that in the Antarctic ozone hole. Unusually long-lasting cold conditions in the Arctic lower stratosphere led to persistent enhancement in ozone-destroying forms of chlorine and to unprecedented ozone loss, which exceeded 80 per cent over 18-20 kilometres altitude. Our results show that Arctic ozone holes are possible even with temperatures much milder than those in the Antarctic. We cannot at present predict when such severe Arctic ozone depletion may be matched or exceeded.

Constraining the chlorine monoxide (ClO)/chlorine peroxide (ClOOCl) equilibrium constant from Aura Microwave Limb Sounder measurements of nighttime ClO.

The primary ozone loss process in the cold polar lower stratosphere hinges on chlorine monoxide (ClO) and one of its dimers, chlorine peroxide (ClOOCl). Recently, analyses of atmospheric observations have suggested that the equilibrium constant, K(eq), governing the balance between ClOOCl formation and thermal decomposition in darkness is lower than that in the current evaluation of kinetics data. Measurements of ClO at night, when ClOOCl is unaffected by photolysis, provide a useful means of testing quantitative understanding of the ClO/ClOOCl relationship. Here we analyze nighttime ClO measurements from the National Aeronautics and Space Administration Aura Microwave Limb Sounder (MLS) to infer an expression for K(eq). Although the observed temperature dependence of the nighttime ClO is in line with the theoretical ClO/ClOOCl equilibrium relationship, none of the previously published expressions for K(eq) consistently produces ClO abundances that match the MLS observations well under all conditions. Employing a standard expression for K(eq), A x exp(B/T), we constrain the parameter A to currently recommended values and estimate B using a nonlinear weighted least squares analysis of nighttime MLS ClO data. ClO measurements at multiple pressure levels throughout the periods of peak chlorine activation in three Arctic and four Antarctic winters are used to estimate B. Our derived B leads to values of K(eq) that are approximately 1.4 times smaller at stratospherically relevant temperatures than currently recommended, consistent with earlier studies. Our results are in better agreement with the newly updated (2009) kinetics evaluation than with the previous (2006) recommendation.