A climatology of surface ozone in the extra tropics: cluster analysis of observations and model results

[摘要] Important aspects of the seasonal variations of surface ozone are discussed.The underlying analysis is based on the long-term (1990–2004) ozone recordsof the Co-operative Programme for Monitoring and Evaluation of theLong-range Transmission of Air Pollutants in Europe (EMEP) and the WorldData Centre of Greenhouse Gases, which provide data mostly for the NorthernHemisphere. Seasonal variations are pronounced at most of the 114 locationsat all times of the day. A seasonal-diurnal variations classification usinghierarchical agglomeration clustering reveals 6 distinct clusters: cleanbackground, rural, semi-polluted non-elevated, semi-polluted semi-elevated,elevated and polar/remote marine. For the "clean background" cluster theseasonal maximum is observed in March-April, both for night and day. Forthose sites with a double maximum or a wide spring-summer maximum, thespring maximum appears both for day and night, while the summer maximum ismore pronounced for daytime and hence can be attributed to photochemicalprocesses. The spring maximum is more likely caused by dynamical/transportprocesses than by photochemistry as it is observed in spring for all timesof the day. We compare the identified clusters with corresponding data fromthe 3-D atmospheric chemistry general circulation model ECHAM5/MESSy1covering the period of 1998–2005. For the model output as for themeasurements 6 clusters are considered. The simulation shows at most of thesites a spring seasonal maximum or a broad spring-summer maximum (withhigher summer mixing ratios). For southern hemispheric and polar remotelocations the seasonal maximum in the simulation is shifted to spring, whilethe absolute mixing ratios are in good agreement with the measurements. Theseasonality in the model cluster covering background locations ischaracterized by a pronounced spring (April–May) maximum. For the modelclusters which cover rural and semi-polluted sites the role of thephotochemical production/destruction seems to be overestimated. Taking intoconsideration the differences in the data sampling procedure, the comparisondemonstrates the ability of the model to reproduce the main regimes ofsurface ozone variations quite well.

[学科分类] 大气科学