Quantifying the drivers of inter-annual variability in the atmospheric levels of the ozone-depleting trace gas methyl bromide

Abstract:

Methyl bromide is an important ozone-depleting gas with production phased out or regulated as part of the Montreal Protocol. The global budget of methyl bromide is now mainly controlled by natural processes that are sensitive to climate. In the Halocarbons and other Atmospheric Trace Species (HATS) group in the Global Monitoring Laboratory at NOAA Earth System Research Laboratories, observations of the abundance of methyl bromide have been made at several surface sites globally for the past 25+ years. In this study, we are focused on understanding and quantifying the drivers of the variability in methyl bromide atmospheric levels over the past two decades. The surface observations show interannual variability in methyl bromide mixing ratios that are strongly correlated with the temporal trends in the El Niño Southern Oscillation, particularly with the positive, El Niño phase. Using a multi-box atmospheric and oceanic model, we investigate which sources and/or sinks are responsible for the large variations in methyl bromide mixing ratios during El Niño events. Using this information, it is possible to gain insight into how the budget of methyl bromide, and ultimately stratospheric ozone levels, could be impacted by future climate change.