Spatiotemporal variations of ozone exposure and its risks to vegetation and human health in Cyprus: an analysis across a gradient of altitudes

Ground-level ozone (O 3 ) 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 O 3 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 O 3 are poorly understood and the potential risks for forest health have not been explored. We evaluated O 3 and nitrogen oxides (NO and NO 2 ) at four regional background stations at different altitudes over 2014−2016. O 3 risks to vegetation and human health were estimated by calculating accumulated O 3 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 O 3 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 O 3 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 O 3 (NO x ), driven by summer–winter differences. The diurnal patterns of O 3 showed little variation. Only at the lowest altitude O 3 displayed a typical O 3 diurnal pattern, with hourly differences smaller than 15 nmol mol −1 . Accumulated O 3 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. O 3 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 O 3 is a major environmental and public health issue in Cyprus, and policies must be adopted to mitigate O 3 precursor emissions at local and regional scales.