The rescaled range (R/S) analysis was used for analyzing the statistical persistence of air
pollutants in Mexico City. The air-pollution time series consisted of hourly observations
of ozone, nitrogen dioxide, sulfur dioxide and particulate matter obtained at the Mexico
City downtown monitoring station during 1999–2014. The results showed that long-range
persistence is not a uniform property over a wide range of time scales, from days to months.
In fact, although the air pollutant concentrations exhibit an average persistent behavior,
environmental (e.g., daily and yearly) and socio-economic (e.g., daily and weekly) cycles
are reflected in the dependence of the persistence strength as quantified in terms of the
Hurst exponent. It was also found that the Hurst exponent exhibits time variations, with the
ozone and nitrate oxide concentrations presenting some regularity, such as annual cycles.
The persistence dynamics of the pollutant concentrations increased during the rainy season
and decreased during the dry season. The time and scale dependences of the persistence
properties provide some insights in the mechanisms involved in the internal dynamics of
the Mexico City atmosphere for accumulating and dissipating dangerous air pollutants.
While in the short-term individual pollutants dynamics seems to be governed by specific
mechanisms, in the long-term (for monthly and higher scales) meteorological and seasonal