New research in the Journal of Geophysical Research: Atmospheres reassesses the global methyl bromide budget using the 25-year record of atmospheric measurements from the NOAA Global Monitoring Laboratory global flask network. GML scientists Melinda Nicewonger and Stephen Montzka along with collaborators from the University of California, Irvine and Texas A&M University are co-authors of the publication. The research is funded in part by CPO’s AC4 program.
Since the Phase-out under the Montreal Protocol in 1999, atmospheric methyl bromide levels have declined significantly. The atmosphere appears to have reached a new steady-state during the past five years. Previous research had identified a gap between known sources and losses of this potent ozone-depleting gas. However, the last budget assessment happened in 2009, and scientific knowledge of ocean/atmospheric processes has advanced since then.
Using an updated global ocean/atmosphere model, the authors estimated total methyl bromide emissions from atmospheric measurements between 1995 and 2019. The results indicate a significant decrease from about 120 to 85 Gigagrams per year in global land-based emissions and a slight increase from -5 to +5 Gigagrams per year in net ocean emissions from 1995 to 2019. Consistent with previous studies, the authors found an imbalance between the model-derived emissions and the bottom-up estimates of sources. However, the gap (20 Gigagrams per year) is 35 percent smaller than previously reported. A persistent source is identified primarily in the tropics, likely originating from natural vegetative emissions. A smaller time-varying source was found to scale with the anthropogenic source during phase-out, suggesting the possibility of human emissions being slightly underestimated.
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