a decreasing trendp < 0.05
The statistical analysis of the time-behavior for CO 2 concentrations measured during the whole monitoring period indicated that the series was not stationary (KPSS test, p < 0.05, presence of a decreasing trend) and that the rankings of values were not random ( runs test, p < 0.05; Kwiatkowski et al., 1992 ; Alhakim and Hooper, 2008 ).