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

K H Bates,D J Jacob

doi:10.1029/2019gl084486

Abstract

AbstractModels of tropospheric ozone commonly define an “odd oxygen” family (Ox), comprising ozone and species with which it rapidly cycles, in order to compute tropospheric ozone budgets and lifetimes. A major Ox loss is the O(1D) + H2O → 2OH reaction, but this may not be an actual loss because the resulting hydrogen oxide (HOx) radicals regenerate ozone in the presence of nitrogen oxides. Here we introduce an expanded odd oxygen family, Oy≡ Ox + Oz, to include both Ox and an additional subfamily, Oz, consisting of HOx 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 Ox budget. Tracking the Oy budget may provide better understanding of the discrepancies between global models in their computations of ozone sources and sinks.

Highlights

IntroductionTropospheric ozone (O3 ) is an important atmospheric oxidant and greenhouse gas, and is estimated to be responsible for over one million respiratory deaths annually (Malley et al, 2017)
Tropospheric ozone (O3 ) is an important atmospheric oxidant and greenhouse gas, and is estimated to be responsible for over one million respiratory deaths annually (Malley et al, 2017). It is produced within the troposphere by photochemical oxidation of volatile organic compounds (VOCs) and carbon monoxide (CO) in the presence of nitrogen oxide radicals (NOx ≡ NO + NO2 )
We propose here an expanded definition of the odd oxygen family, Oy ≡ Ox + Oz, to enable rigorous accounting of tropospheric ozone budgets

Summary

Introduction

Tropospheric ozone (O3 ) is an important atmospheric oxidant and greenhouse gas, and is estimated to be responsible for over one million respiratory deaths annually (Malley et al, 2017). The first approach does not resolve the origin of the HOx required for ozone formation, and the second approach underestimates the effective lifetime of ozone by not accounting for its cycling with HOx. To overcome the inconsistencies described above, a proper treatment of the odd oxygen budget should reference production and loss to O2 and H2 O, the main forms of tropospheric oxygen and hydrogen, while recognizing the importance of NOx in converting peroxy radicals to ozone. We propose an expanded odd oxygen family, Oy ≡ Ox + Oz , as the sum of Ox and a reservoir Oz that includes HOx radicals, atomic halogen radicals, and their reservoirs This new formulation is analogous to other extended atmospheric chemical families used to denote cycling between species and their reservoirs, for example NOy ≡ NOx + NOz where the NOz reservoir includes HNO3 , PANs, etc.

O2 deposition

Chemical loss to H2O

Findings

Conclusions