Long-term surface ozone variability at Mt. Cimone WMO/GAW global station (2165 m a.s.l., Italy)

Overall, a significant positive (95% confidence level) linear trend in monthly O3 mole fraction was observed over the period 1991-2011 (0.21 ± 0.10 nmol/mol yr−1) while no trend (-0.02 ± 0.12 nmol/mol yr−1) was detected for the 1996-2011, when measurements were carried out by an homogeneous experimental set-up. On a seasonal basis, a positive trend has been observed for 1996-2011 (0.34 ± 0.32 nmol/mol yr−1) only for spring. Significant decreases of the seasonal O3 growth-rates have been detected at CMN during 1991-2011 from winter to spring and only for summer during 1996-2011.