Stratospheric impact on tropospheric ozone variability and trends: 1990–2009

P G Hess,R Zbinden

doi:10.5194/acp-13-649-2013

Abstract

Abstract. The influence of stratospheric ozone on the interannual variability and trends in tropospheric ozone is evaluated between 30 and 90° N from 1990–2009 using ozone measurements and a global chemical transport model, the Community Atmospheric Model with chemistry (CAM-chem). Long-term measurements from ozonesondes, at 150 and 500 hPa, and the Measurements of OZone and water vapour by in-service Airbus aircraft programme (MOZAIC), at 500 hPa, are analyzed over Japan, Canada, the Eastern US and Northern and Central Europe. The measurements generally emphasize northern latitudes, although the simulation suggests that measurements over the Canadian, Northern and Central European regions are representative of the large-scale interannual ozone variability from 30 to 90° N at 500 hPa. CAM-chem is run with input meteorology from the National Center for Environmental Prediction; a tagging methodology is used to identify the stratospheric contribution to tropospheric ozone concentrations. A variant of the synthetic ozone tracer (synoz) is used to represent stratospheric ozone. Both the model and measurements indicate that on large spatial scales stratospheric interannual ozone variability drives significant tropospheric variability at 500 hPa and the surface. In particular, the simulation and the measurements suggest large stratospheric influence at the surface sites of Mace Head (Ireland) and Jungfraujoch (Switzerland) as well as many 500 hPa measurement locations. Both the measurements and simulation suggest the stratosphere has contributed to tropospheric ozone trends. In many locations between 30–90° N 500 hPa ozone significantly increased from 1990–2000, but has leveled off since (from 2000–2009). The simulated global ozone budget suggests global stratosphere-troposphere exchange increased in 1998–1999 in association with a global ozone anomaly. Discrepancies between the simulated and measured ozone budget include a large underestimation of measured ozone variability and discrepancies in long-term stratospheric ozone trends. This suggests the need for more sophisticated simulations including better representations of stratospheric chemistry and circulation.

Highlights

Tropospheric ozone is photochemically produced in situ from ozone precursor emissions or transported from the stratosphere
Using conservative ozonemortality epidemiologic relationships (Bell et al, 2004), even one ppbv of ozone, currently approximately 20 % of the surface ozone attributed to Stratosphere-Troposphere Exchange (STE) in the Northern Hemisphere (NH) mid- and high latitudes (Hess and Lamarque, 2007) may have relatively large consequences on human health (West et al, 2007)
The analysis presented below indicates that on large spatial scales stratospheric interannual ozone variability drives significant tropospheric ozone variability

Summary

Introduction

Tropospheric ozone is photochemically produced in situ from ozone precursor emissions or transported from the stratosphere. Tropospheric ozone impacts air quality and human health (Bell et al, 2004), atmospheric radiative forcing (Forster and Shine, 1997), and ecosystem productivity (UNEP, 2006) with resulting impacts on food (Chameides et al, 1994; Van Dingenen et al, 2009) and climate (Sitch et al, 2007) It modifies the “oxidizing capacity” of the troposphere, impacting the lifetime and radiative forcing of methane (Fiore et al, 2002). Using conservative ozonemortality epidemiologic relationships (Bell et al, 2004), even one ppbv of ozone, currently approximately 20 % of the surface ozone attributed to Stratosphere-Troposphere Exchange (STE) in the Northern Hemisphere (NH) mid- and high latitudes (Hess and Lamarque, 2007) may have relatively large consequences on human health (West et al, 2007).

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Conclusion