Using three methods to investigate time-scaling properties in air pollution indexes time series

The three pollution indexes (SO2SO2, NO2NO2 and PM10PM10) and the daily air pollution indexes (APIs) of Shanghai in China are analyzed by rescaled range analysis (R/S)(R/S), detrended fluctuation analysis (DFA) and spectral analysis. The results show that the temporal scaling behaviors in all the four series exhibit two different power laws. In shorter temporal scaling, all the series indicate the similar persistence corresponding to the annual cycle. However, in longer temporal scaling, the trends are different for the four series, which reflect the different inherent dynamic nature of various pollutant series. The fluctuations of Hurst exponent (H)(H), DFA exponent (α)(α) and power spectral density index (β)(β) with increasing threshold magnitude are analyzed. Our results suggest that there are different self-organized critical states in these air pollutants.