Nowcasting of air pollution episodes in megacities: A case study for Athens, Greece

The main objective of the present study is to develop a model for the prediction of the extreme events of air pollution in megacities using the concept of so-called natural time instead of the conventional clock time. In particular, we develop a new nowcasting technique based on a statistically significant fit to the law of GutenbergRichter of the surface concentration of ozone (O3), particles of the size fraction less than 10 mu m (PM-10) and nitrogen dioxide (NO2). Studying the air pollution over Athens, Greece during the period 2000-2018, we found that the average waiting time between successive extreme concentrations values varied between different atmospheric parameters accounted as 17 days in case of O3, 29 days in case of PM-10 and 28 days in case of NO2. This average waiting time depends on the upper threshold of the maximum extreme concentrations of air pollutants considered. For instance, considering the NO2 concentrations over Athens it was found that the average waiting time is 13 days for 130 mu g/m3 and 2.4 years for 200 mu g/m3. Remarkably, the same behaviour of obedience to the Guttenberg-Richter law characterizing the extreme values of the air pollution of a megacity was found earlier in other long-term ecological and paleoclimatic variables. It is a sign of self-similarity that is often observed in nature, which can be used in the development of more reliable nowcasting models of extreme events.

Automated summary

The study aims to develop a model for predicting extreme air pollution events in megacities using natural time concept. The findings show that the average waiting time between extreme concentration values varies for different atmospheric parameters and depends on the upper threshold of maximum extreme concentrations of air pollutants. The study reveals a self-similarity behavior following the Gutenberg-Richter law, which can be utilized for developing reliable nowcasting models of extreme events.