1NOAA ESRL Chemical Sciences Division, 325 Broadway, Boulder, CO, USA
2UPMC Univ. Paris 06, Univ. Versailles Saint-Quentin, CNRS/INSU, UMR8190, LATMOS/IPSL, Paris, France
3Institute for Atmospheric and Climate Science, ETHZ, Universitätstrasse 16, 8092 Zürich, Switzerland
4rdscientific, Newbury, Berkshire RG14 6LH, UK
5CIRES, University of Colorado, Boulder, CO, USA
6National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan
7IEK-8, Forschungszentrum Juelich, 52425 Juelich, Germany
8Hohenpeissenberg Meteorological Observatory, German Meteorological Service (DWD), Hohenpeissenberg, Germany
9Karlsruhe Institute of Technology, IMK-IFU, 82467 Garmisch-Partenkirchen, Germany
10Swiss Federal Laboratories for Materials Science and Technology (EMPA), Duebendorf, Switzerland
11Science and Technology Branch, Environment Canada, 4905 Dufferin Street, Toronto, Ontario, Canada
Received: 10 Apr 2012 – Discussion started: 05 Jun 2012
Abstract. Changes in baseline (here understood as representative of continental to hemispheric scales) tropospheric O3 concentrations that have occurred at northern mid-latitudes over the past six decades are quantified from available measurement records with the goal of providing benchmarks to which retrospective model calculations of the global O3 distribution can be compared. Eleven data sets (ten ground-based and one airborne) including six European (beginning in the 1950's and before), three North American (beginning in 1984) and two Asian (beginning in 1991) are analyzed. When the full time periods of the data records are considered a consistent picture emerges; O3 has increased at all sites in all seasons at approximately 1% yr−1 relative to the site's 2000 yr mixing ratio in each season. For perspective, this rate of increase sustained from 1950 to 2000 corresponds to an approximate doubling. There is little if any evidence for statistically significant differences in average rates of increase among the sites, regardless of varying length of data records. At most sites (most definitively at the European sites) the rate of increase has slowed over the last decade (possibly longer), to the extent that at present O3 is decreasing at some sites in some seasons, particularly in summer. The average rate of increase before 2000 shows significant seasonal differences (1.08 ± 0.09, 0.89 ± 0.10, 0.85 ± 0.11 and 1.21 ± 0.12% yr−1 in spring, summer, autumn and winter, respectively, over North America and Europe).
Revised: 06 Nov 2012 – Accepted: 16 Nov 2012 – Published: 04 Dec 2012
Parrish, D. D., Law, K. S., Staehelin, J., Derwent, R., Cooper, O. R., Tanimoto, H., Volz-Thomas, A., Gilge, S., Scheel, H.-E., Steinbacher, M., and Chan, E.: Long-term changes in lower tropospheric baseline ozone concentrations at northern mid-latitudes, Atmos. Chem. Phys., 12, 11485-11504, doi:10.5194/acp-12-11485-2012, 2012.