资源环境科技发展态势分析平台

We derived interannual variations in the global oxidation of MCF that bring simulated mole fractions of MCF within 1–2 % of the assimilated observations from the NOAA-GMD surface network at most sites. Additionally, the posterior simulations better reproduce aircraft observations used for independent validation. The derived OH variations showed robustness with respect to the prior MCF emissions and the prior OH distribution. The interannual variations were typically small (< 3 %/year), with no significant longterm trend in OH.

The inverse system found strong adjustments of the latitudinal distribution of OH, with systematic increases in tropical OH and decreases in extra-tropical OH (both up to 30 %). These spatial adjustments were driven by intrahemispheric biases in simulated MCF mole fractions, which have not been identified in previous studies. Given the unexpectedly large amplitude of these adjustments and a residual bias in intrahemispheric gradients, we suggest a reversal in the extratropical ocean sink of MCF in response to declining atmospheric MCF abundance (as hypothesized in Wennberg et al., 2004). This reversal provides a more realistic explanation for the biases, possibly complimentary to adjustments in the OH distribution.

While we identified significant added value in the use of a 3D transport model over simpler box models, we also found a trade-off in computational expense and convergence problems. However, although the signals are small compared to assuming interannually repeating OH, the derived variations better match the global MCF observations and are relevant for studying the budget of e.g. CH₄.