Nonlinear dynamical analysis of ground level ozone concentrations at different temporal scales

The nonlinear dynamical analysis of ground level ozone concentration is carried out by using correlation integral method to examine its scale invariance property. The dynamics of the time series is often studied at one temporal scale. It is assumed that if the time series is determined to be chaotic at one temporal scale, its behavior at another scale can be determined as the scale shifts are allowed due to scale invariance property. The actual dynamics at other scales is however not yet analyzed. The assumption of scale invariance of the time series at different time scales is tested in this study. The analysis is carried out for ground ozone levels observed during 2006 at two sites of different land use characteristics, as traffic and mixed-use in Delhi at four temporal scales as 1 h, 4 h, 8 h and 24 h. The chaotic nature is observed for the ozone concentration with 1 h and 4 h frequency, whereas at 8 h and 24 h time scale, the ozone concentration shows random behavior. As expected, a decrease in the variability is observed in the ozone levels with increase in the scales from 1 h to 24 h. The results indicated the temporal scale shifts are allowed from 1 h to 4 h resolution and vice versa. The ozone time series at 8 h and 24 h scalings however, should be dealt separately. Further analysis for corresponding NO₂ concentration at two sites suggested finite d₂ for 1 h, 4 h and 8 h scalings with higher value at traffic site than that at mixed-use site. The analysis also indicated same degrees of freedom for ozone and NO₂ concentration at traffic site whereas at mixed-use site the number of variables governing the NO₂ pollution are less than the ozone concentration.