An Expanded Definition of the Odd Oxygen Family for Tropospheric Ozone Budgets: Implications for Ozone Lifetime and Stratospheric Influence

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( 1 D ) + H 2 O → 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. Here we introduce an expanded odd oxygen family, O y ≡ O x + O z , to include both O x and an additional subfamily, O z , consisting of HO x and its reservoirs. We incorporate this new accounting into the GEOS‐Chem model, revealing a longer global mean ozone lifetime (73 days vs. 24 days) and greater stratospheric contribution (26% vs. 9%) under present‐day conditions than derived from the standard O x budget. Tracking the O y budget may provide better understanding of the discrepancies between global models in their computations of ozone sources and sinks.