Spatiotemporal variations of tropospheric ozone in Spain (2008-2019).

This study aims to support the development of Spain's Ozone Mitigation Plan by evaluating the present-day spatial variation (2015-2019) and trends (2008-2019) for seven ground-level ozone (O ₃ ) metrics relevant for human/ecosystems exposure and regulatory purposes. Results indicate that the spatial variation of O ₃ depends on the part of the O ₃ distribution being analyzed. Metrics associated with moderate O ₃ concentrations depict an increasing O ₃ gradient between the northern and Mediterranean coasts due to climatic factors, while for metrics considering the upper end of the O ₃ distribution, this climatic gradient tends to attenuate in favor of hotspot regions pointing to relevant local/regional O ₃ formation. A classification of atmospheric regions in Spain is proposed based on their O ₃ pollution patterns, to identify priority areas (or O ₃ hotspots) where local/regional precursor abatement might significantly reduce O ₃ during pollution episodes. The trends assessment reveals a narrowing of the O ₃ distribution at the national level, with metrics influenced by lower concentrations tending to increase over time, and those reflecting the higher end of the O ₃ distribution tending to decrease. While most stations show no statistically significant variations, contrasting O ₃ trends are evident among the O ₃ hotspots. The Madrid area exhibits the majority of upward trends across all metrics, frequently with the highest increasing rates, implying increasing O ₃ associated with both chronic and episodic exposure. The Valencian Community area exhibits a mixed variation pattern, with moderate to high O ₃ metrics increasing and peak metrics decreasing, while O ₃ in areas downwind of Barcelona, the Guadalquivir Valley and Puertollano shows no variations. Sevilla is the only large Spanish city with generalized O ₃ decreasing trends. The different O ₃ trends among hotspots highlight the need for mitigation measures to be designed at a local/regional scale to be effective. This approach may offer valuable insights for other countries developing O ₃ mitigation plans.
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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