Fig. 2.

Lomb–Scargle periodograms for selected meteorological, traffic count, and pollutant time series data with significant spectral peaks identified by their respective period (T, in units of days). The significance bounds were generated using bootstrap techniques and AR(1) simulations as described in the text. The characters at the bottom of each plot identify the positioning of potential annual (a), monthly (m) and weekly (w) periods. In addition, the positioning of the first (w’) and second (w”) harmonics for the weekly period is depicted.