PM_2.5 Characterization and Source Apportionment Using Positive Matrix Factorization at San Luis Potosi City, Mexico, during the Years 2017–2018

Abstract

In growing Mexican cities, there are few studies on air pollution, especially on the topic of characterization for the chemical composition of Particulate Matter (PM). This work presents an X-ray Fluorescence (XRF) analysis and Total Carbon analysis of PM2.5 in a two-year monitoring campaign from 20 May 2017 to 30 July 2018, collecting 96 daily samples in the northeast area of San Luis Potosi city to reconstruct the gravimetric mass and perform a source apportionment study using the Positive Matrix Factorization model (PMF). Concentration differences were due to different yearly seasons. In the year 2017, there was a major influence on heavy metals (V, Cr, Mn, Ni, Cu, Zn, Pb), and for the year 2018, there was a major crustal elements concentration (Na, Al, Si, P). Heavy metal concentrations are higher than any worldwide regulation limit. After applying these methods to the 49 samples collected for the year 2017, the mass reconstruction was nearly 70% of the gravimetric mass. XRF analysis quantified 17 elements (Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn) in addition to Total Carbon (Organic Carbon (OC) + Elemental Carbon (EC)). PMF receptor model was applied to identify possible contribution sources and resolved seven physically interpretable factors that contributed to the ambient particulate pollution at the sampling site: Urban Dust (24.2%), Mobile Sources (22.2%), Chemical industry (18.2%), Oil combustion (16.3%), Smelting Industry (12.4%), Fuel Oil + Ceramic Industry (4.4%), and Braking (2.3%). However, the brick kiln’s emissions may be present in at least four of the emission sources due to several types of combustible employed.

Keywords

• particulate matter
• PM_2.5
• positive matrix factorization
• San Luis Potosi
• Mexico