An analysis of ozone variation in the Greater Athens Area using Granger Causality

Air pollution in urban areas is a topic of interest for many researchers as it impacts negatively the human health, the environment and the quality of life. As part of the effort in exploring ways for efficient and timely assessment of the urban air pollution patterns and their association with the local meteorology and photochemistry, an advanced statistical approach is proposed for the analysis of the spatiotemporal ozone (O-3) variations and interdependencies to other pollutants. The focus of the work is placed on the investigation and determination of the causality between the local and regional factors causing the observed ozone variability, by applying a holistic methodology on multiple-year meteorological data and air pollution monitoring data, referenced in Athens (Greece). The methodology includes the Positive Matrix Factorization (PMF), for data scaling and reduction, a k-means clustering algorithm, for determining groups of data with common properties, and importantly, the Granger Causality test, for obtaining the causal links between the ozone and nitrogen oxides as well as the local meteorological conditions. The methodology revealed six dominant combined patterns of weather and air pollution. The application of the Granger Causality allowed the determination of relationships across the pollution patterns of dispersed geographic locations and the interdependence of those with the local meteorological conditions and photochemistry effects.