An expanded definition of the odd oxygen family for tropospheric ozone budgets: Implications for ozone lifetime, stratospheric influence, and source tagging (Invited Presentation)

Models of tropospheric ozone commonly define an ”odd oxygen” family (O_x), comprising ozone and species with which it rapidly cycles, in order to compute tropospheric ozone budgets and lifetimes. A major O_x loss is the O(¹D) + H₂O → 2OH reaction, but this may not be an actual loss because the resulting hydrogen oxide (HO_x) radicals regenerate ozone in the presence of nitrogen oxides. We recently introduced an expanded odd oxygen family, O_y ≡ O_x + O_z, to include both the traditional O_x and an additional subfamily, O_z, consisting of HO_x and its reservoirs. Here, we demonstrate the application of this expanded odd oxygen family in the computation of ozone budgets and in both source perturbation and ozone tagging simulations using GEOS-Chem, a global chemical transport model. We show that the O_y framework reveals a longer tropospheric mean lifetime of ozone (73 davs vs. 24 days) and greater stratospheric contribution (26% vs. 9%) than derived from the standard O_x budget. In perturbation experiments, changes in nitrogen oxide (NO_x) emissions lead to changes in the efficiency of cycling between the O_y subfamilies, altering the balance between O_x and O_z, which in turn helps to explain the non-linearities inherent to the ozone budget. In tagging simulations, ozone can be tracked both by its primary sources and by the number of cycles it undergoes between O_x and O_z, revealing the spatial and temporal variability in tropospheric ozone lifetime, primary source influence, and cycling efficiency. Tracking the O_y budget may provide better understanding of the discrepancies between global models in their computations of ozone sources and sinks.