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Contrasting ozone responses driven by Mediterranean ventilation and anticyclonic blocking under high-temperatures in coastal Southwestern Europe.

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Title: Contrasting ozone responses driven by Mediterranean ventilation and anticyclonic blocking under high-temperatures in coastal Southwestern Europe.
Authors: Adame, J.A.1 (AUTHOR) adamecj@inta.es, Gutierrez-Alvarez, I.2 (AUTHOR), Notario, A.3 (AUTHOR), Yela, M.4 (AUTHOR)
Source: Atmospheric Research. Jan2026, Vol. 327, pN.PAG-N.PAG. 1p.
Subjects: Ozone, Global warming, Air quality, High temperatures, Coasts, Blocking (Meteorology), Ventilation
Geographic Terms: Strait of Gibraltar, Mediterranean Sea, Europe
Abstract: The contrasting responses of surface ozone to high-temperature conditions were investigated at El Arenosillo coastal observatory (southwestern Europe) using 24 years of data (2000–2023). Two event types were defined: high-ozone/high-temperature (HOHT) and low-ozone/high-temperature (LOHT) events. A total of 52 HOHT and 291 LOHT events were identified, with a fourfold decline in HOHT frequency during the later decade (2012−2023) compared to 2000–2011. On average, HOHT days recorded 15.4 ± 7.9 ppb more ozone than LOHT days, with differences peaking at 30 ppb. Temperature increases during LOHT events reached up to 7.1 °C. Two representative cases were analysed, both exceeding 30 °C and dominated by coastal breeze circulation, yet displaying opposite ozone behaviours. HOHT events were associated with anticyclonic ridging over central Europe, northerly flow from southern Portugal , and easterly winds through the Strait of Gibraltar , facilitating ozone transport from Portugal and the western Mediterranean, which was subsequently trapped inland by sea breezes. In contrast, LOHT events coincided with a weakened anticyclone and a deeper Icelandic Low, blocking Mediterranean ventilation and inducing westerly flow in the Strait, which diverted ozone transport eastward and inhibited accumulation locally. These contrasting circulation patterns may shift in frequency under global warming, potentially reducing ozone pollution in this coastal area while enhancing it elsewhere in the western Mediterranean. Understanding the evolving role of large-scale dynamics is critical to anticipate future ozone variability and heat extremes in this transitional region between marine and continental influences. • HOHT and LOHT events analysed at an Atlantic coastal site (2000−2023). • Mediterranean ventilation and external input enhance HOHT events. • Anticyclonic blocking in the Mediterranean favours LOHT events. • High temperatures and breezes alone are insufficient for ozone formation. • LOHT events may become more frequent under global warming scenarios. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:The contrasting responses of surface ozone to high-temperature conditions were investigated at El Arenosillo coastal observatory (southwestern Europe) using 24 years of data (2000–2023). Two event types were defined: high-ozone/high-temperature (HOHT) and low-ozone/high-temperature (LOHT) events. A total of 52 HOHT and 291 LOHT events were identified, with a fourfold decline in HOHT frequency during the later decade (2012−2023) compared to 2000–2011. On average, HOHT days recorded 15.4 ± 7.9 ppb more ozone than LOHT days, with differences peaking at 30 ppb. Temperature increases during LOHT events reached up to 7.1 °C. Two representative cases were analysed, both exceeding 30 °C and dominated by coastal breeze circulation, yet displaying opposite ozone behaviours. HOHT events were associated with anticyclonic ridging over central Europe, northerly flow from southern Portugal , and easterly winds through the Strait of Gibraltar , facilitating ozone transport from Portugal and the western Mediterranean, which was subsequently trapped inland by sea breezes. In contrast, LOHT events coincided with a weakened anticyclone and a deeper Icelandic Low, blocking Mediterranean ventilation and inducing westerly flow in the Strait, which diverted ozone transport eastward and inhibited accumulation locally. These contrasting circulation patterns may shift in frequency under global warming, potentially reducing ozone pollution in this coastal area while enhancing it elsewhere in the western Mediterranean. Understanding the evolving role of large-scale dynamics is critical to anticipate future ozone variability and heat extremes in this transitional region between marine and continental influences. • HOHT and LOHT events analysed at an Atlantic coastal site (2000−2023). • Mediterranean ventilation and external input enhance HOHT events. • Anticyclonic blocking in the Mediterranean favours LOHT events. • High temperatures and breezes alone are insufficient for ozone formation. • LOHT events may become more frequent under global warming scenarios. [ABSTRACT FROM AUTHOR]
ISSN:01698095
DOI:10.1016/j.atmosres.2025.108350