Regional responses of surface ozone in Europe to the location of high-latitude blocks and subtropical ridges

Ordóñez C, Barriopedro D, García-Herrera R, Sousa PM, Schnell JL
Atmos. Chem. Phys. 17: 3111-3131. doi: 10.5194/acp-17-3111-2017

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This paper analyses for the first time the impact of high-latitude blocks and subtropical ridges on near-surface ozone (O3/ in Europe during a 15-year period. For this purpose, a catalogue of blocks and ridges over the Euro–Atlantic region is used together with a gridded dataset of maximum daily 8 h running average ozone (MDA8 O3/ covering the period 1998–2012. The response of ozone to the location of blocks and ridges with centres in three longitudinal sectors (Atlantic, ATL, 30–0ºW; European, EUR, 0–30º E; Russian, RUS, 30–60º E) is examined. The impact of blocks on ozone is regionally and seasonally dependent. In particular, blocks within the EUR sector yield positive ozone anomalies of ~5–10 ppb over large parts of central Europe in spring and northern Europe in summer. Over 20 and 30% of the days with blocks in that sector register exceedances of the 90th percentile of the seasonal ozone distribution at many European locations during spring and summer, respectively. The impacts of ridges during those seasons are subtle and more sensitive to their specific location, although they can trigger ozone anomalies above 10 ppb in northern Italy and the surrounding countries in summer, eventually exceeding European air quality (AQ) targets. During winter, surface ozone in the north-west of Europe presents completely opposite responses to blocks and ridges. The anticyclonic circulation associated with winter EUR blocking, and to a lesser extent with ATL blocking, yields negative ozone anomalies between