Statistical persistence analysis of hourly ground level ozone concentrations in Delhi

Persistence in hourly ground level ozone concentration observed during 2006 at two sites in Delhi is analyzed using rescaled range analysis based on Hurst exponent estimation. The analysis is carried out separately for whole data series and monthly time series to investigate the seasonal effects on the results of the analysis. High intermittence in the original ozone concentrations at traffic site and in the differenced ozone concentration at both traffic and mixed-use site is observed. The results showed break in the scaling behavior with persistence up to 5 days in the ozone concentration over 2006. The differencing however purged the persistence property. For the monthly observations, persistence is observed up to 2 days. In the monthly time series also, differencing resulted in low persistence as compared to original one during all the months at two sites except during July and August at traffic site, where random behavior is observed. This is mainly attributed to high and intermittent concentration of ozone due to high VOC emissions. Except these months, the behavior of ozone pollution in the observed period is observed to be causal and governed by the temporal dependence on the previous ozone levels and atmospheric processes. The results indicated the differencing has significant effect on the persistence property of the time series.