Abstract:

Ground-level ozone (O₃) affects vegetation and threatens environmental health when levels exceed critical values, above which adverse effects are expected. Cyprus is expected to be a hotspot for O₃ concentrations due to its unique position in the eastern Mediterranean, receiving air masses from Europe, African, and Asian continents, and experiencing a warm Mediterranean climate. In Cyprus, the spatiotemporal features of O₃ are poorly understood and the potential risks for forest health have not been explored. We evaluated O₃ and nitrogen oxides (NO and NO₂) at four regional background stations at different altitudes over 2014−2016. O₃ risks to vegetation and human health were estimated by calculating accumulated O₃ exposure over a threshold of 40 nmol mol⁻¹ (AOT40) and cumulative exposure to mixing ratios above 35 nmol mol⁻¹ (SOMO35) indices. The data reveal that mean O₃ concentrations follow a seasonal pattern, with higher levels in spring (51.8 nmol mol⁻¹) and summer (53.2 nmol mol⁻¹) and lower levels in autumn (46.9 nmol mol⁻¹) and winter (43.3 nmol mol⁻¹). The highest mean O₃ exposure (59.5 nmol mol⁻¹) in summer occurred at the high elevation station Mt. Troodos (1819 m a.s.l.). Increasing (decreasing) altitudinal gradients were found for O₃ (NO_x), driven by summer–winter differences. The diurnal patterns of O₃ showed little variation. Only at the lowest altitude O₃ displayed a typical O₃ diurnal pattern, with hourly differences smaller than 15 nmol mol⁻¹. Accumulated O₃ exposures at all stations and in all years exceeded the European Union’s limits for the protection of vegetation, with average values of 3-month (limit: 3000 nmol mol⁻¹ h) and 6-month (limit: 5000 nmol mol⁻¹ h) AOT40 for crops and forests of 16,564 and 31,836 nmol mol⁻¹ h, respectively. O₃ exposures were considerably high for human health, with an average SOMO35 value of 7270 nmol mol⁻¹ days across stations and years. The results indicate that O₃ is a major environmental and public health issue in Cyprus, and policies must be adopted to mitigate O₃ precursor emissions at local and regional scales.

Key words: Air pollution, Ozone risk assessment, Exposure metrics, Vegetation, Human health