Method for the Detection of Functional Outliers Applied to Quality Monitoring Samples in the Vicinity of El Musel Seaport in the Metropolitan Area of Gijón (Northern Spain)

Luis Alfonso Menéndez-García, Paulino José García-Nieto, Esperanza García-Gonzalo, Fernando Sánchez Lasheras, Laura Álvarez- de-Prado () and Antonio Bernardo-Sánchez
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Luis Alfonso Menéndez-García: Department of Mining Technology, Topography and Structures, Higher and Technical School of Mining Engineering, University of León, Campus de Vegazana s/n, 24071 León, Spain
Paulino José García-Nieto: Department of Mathematics, Faculty of Sciences, University of Oviedo, 33007 Oviedo, Spain
Esperanza García-Gonzalo: Department of Mathematics, Faculty of Sciences, University of Oviedo, 33007 Oviedo, Spain
Fernando Sánchez Lasheras: Department of Mathematics, Faculty of Sciences, University of Oviedo, 33007 Oviedo, Spain
Laura Álvarez- de-Prado: Department of Mining Technology, Topography and Structures, Higher and Technical School of Mining Engineering, University of León, Campus de Vegazana s/n, 24071 León, Spain
Antonio Bernardo-Sánchez: Department of Mining Technology, Topography and Structures, Higher and Technical School of Mining Engineering, University of León, Campus de Vegazana s/n, 24071 León, Spain

Mathematics, 2023, vol. 11, issue 12, 1-23

Abstract: Air pollution affects human health and is one of the main problems in the world, including in coastal cities with industrial seaports. In this sense, the city of Gijón (northern Spain) stands out as one of the 20 Spanish cities with the worst air quality. The study aims to identify outliers in air quality observations near the El Musel seaport, resulting from the emissions of six pollutants over an eight-year period (2014–2021). It compares methods based on the functional data analysis (FDA) approach and vector methods to determine the optimal approach for detecting outliers and supporting air quality control. Our approach involves analyzing air pollutant observations as a set of curves rather than vectors. Therefore, in the FDA approach, curves are constructed to provide the best fit to isolated data points, resulting in a collection of continuous functions. These functions capture the behavior of the data in a continuous domain. Two FDA approach methodologies were used here: the functional bagplot and the high-density region (HDR) boxplot. Finally, outlier detection using the FDA approach was found to be more powerful than the vector methods and the functional bagplot method detected more outliers than the HDR boxplot.

Keywords: outlier detection; functional bagplot; functional high-density region (HDR) boxplot; air pollution (search for similar items in EconPapers)
JEL-codes: C (search for similar items in EconPapers)
Date: 2023
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