资源环境科技发展态势分析平台

The distribution of most trace species within the troposphere depends on a complex interplay between chemistry and transport. Holzer and Waugh (2015) introduced the concept of a path- dependent lifetime tau(c)(r), that parameterizes the integrated chemical loss during transport from the source to a given location r. Here we examine whether this parameterization provides a new approach for decoupling transport and chemistry. We present calculations of path-dependent lifetimes for a suite of chlorofluorocarbon replacement gases in a simple 12-box model and show that for trace species with global lifetimes from 0.5 years to 50 years tau(c) provides an accurate representation of the integrated chemical loss during transport. The value of tau(c) is shown to be sensitive to tropical hydroxyl radical (OH) concentrations, with much weaker sensitivity to extratropical OH or transport. Furthermore, fractional changes in Southern Hemisphere extratropical tau(c) are similar to the corresponding fractional changes in tropical OH; that is, a 10% increase in tropical OH results in a 10% decrease in tau(c). This suggests that observation-based estimates of tau(c) may be used to constrain tropical OH concentrations provided that tau(c) can be determined with sufficient precision.