Surface ozone in the southern hemisphere: 20 years of data from a site with a unique setting in El Tololo, Chile
Julien G. Anet1, Martin Steinbacher1, Laura Gallardo2,3, Patricio A. Velásquez Álvarez4, Lukas Emmenegger1, and Brigitte Buchmann11Laboratory for Air Pollution/Environmental Technology, Swiss Federal Laboratories for Materials Science and Technology, Duebendorf, Switzerland 2Departamento de Geofísica de la Universidad de Chile, Blanco Encalada 2002, piso 4, Santiago, Chile 3Center for Climate and Resilience Research (CR2), Blanco Encalada 2002, Santiago, Chile 4Dirección Meteorológica de Chile, Av. Portales 3450, Estación Central, Santiago, Chile
Received: 12 Jul 2016 – Accepted for review: 01 Sep 2016 – Discussion started: 07 Oct 2016
Abstract. The knowledge of surface ozone mole fractions and their global distribution is of utmost importance due to the impact of ozone on human health and ecosystems, and the central role of ozone in controlling the oxidation capacity of the troposphere. The availability of long-term ozone records is far better in the northern than in the southern hemisphere, and recent analyses of the seven accessible records in the southern hemisphere have shown inconclusive trends. Since late 1995, surface ozone is measured in-situ at "El Tololo", a high-altitude (2200 m asl) and pristine station in Chile (30° S, 71° W). The dataset has been recently fully quality-controlled and reprocessed. This study presents the observed ozone trends and annual cycles and identifies key processes driving these patterns. From 1995 to 2010, an overall positive trend of ~ 0.7 ppb/decade is found. Strongest trends per season are observed in March and April. Highest mole fractions are observed in late spring (October) and show a strong correlation with ozone transported from the stratosphere down into the troposphere, as simulated with a model. Over the 20 years of observations, the springtime ozone maximum has shifted to earlier times in the year which, again, is strongly correlated with a temporal shift in the occurrence of the maximum of simulated stratospheric ozone transport at the site. We conclude that background ozone at El Tololo is mainly driven by stratospheric intrusions rather than photochemical production from anthropogenic and biogenic precursors. The major footprint of the sampled air masses is located over the Pacific Ocean. Therefore, due to the negligible influence of local processes, the ozone record also allows studying the influence of El Niño and La Niña episodes on background ozone levels in South America. In agreement with previous studies, we find that during La Niña conditions, ozone mole fractions reach higher levels than during El Niño conditions.
Anet, J. G., Steinbacher, M., Gallardo, L., Velásquez Álvarez, P. A., Emmenegger, L., and Buchmann, B.: Surface ozone in the southern hemisphere: 20 years of data from a site with a unique setting in El Tololo, Chile, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-617, in review, 2016.