Time correlation structure in hourly concentration time series of CO, NOx and O-3 in urban areas

The timescales which govern urban pollution processes are investigated by analyzing variance spectra and structure functions of observational time series. The range of analyzed scales stretches from one hour to several days. It is shown that characteristic fluctuations of CO, NOx (primary pollutants) and O-3 (secondary pollutant) follow a scale invariant law up to timescales of about one day. Scaling exponents indicate the presence of stabilizing feedback mechanisms. Such a scale invariance is broken by the appearance of basic periods which, for primary pollutants, are expressions of traffic dynamics, whereas, for ozone, are closely linked to the diurnal and annual solar cycles.