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 Gutenberg-Richter of the surface concentration of ozone (O₃), particles of the size fraction less than 10 μm (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 NO_2. 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 μg/m³ and 2.4 years for 200 μg/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.

本研究的主要目的是使用所谓的“自然时间”而不是“传统时钟时间”的概念，开发一个模型，用于预测特大城市空气污染的极端事件。特别是，我们开发了一种新的临近预报技术，该技术基于对臭氧 (O ₃ )、粒径小于 10 μm (PM-10) 和二氧化氮表面浓度的古腾堡-里希特定律的统计显着拟合(NO ₂ )。研究 2000 年至 2018 年期间希腊雅典的空气污染，我们发现在 O _{3 的}情况下，不同大气参数之间连续极端浓度值之间的平均等待时间为 17 天，在 PM-10 的情况下为 29 天，在 NO _{2 的}情况下为 28 天_。这个平均等待时间取决于所考虑的最大极端空气污染物浓度的上限。例如，考虑到雅典的 NO ₂浓度，发现 130 μg/m ³的平均等待时间为 13 天，200 μg/m ³的平均等待时间为2.4 年。值得注意的是，在其他长期生态和古气候变量中较早地发现了同样遵循古腾堡-里希特定律的行为，该定律表征了大城市空气污染的极端值。它是自然界中经常观察到的自相似性标志，可用于开发更可靠的极端事件临近预报模型。