Chemical composition and sources of particulate matter across urban and rural sites in the caribbean region of Cienfuegos (Cuba)

Resumen

In Cuba, the study of atmospheric PM pollution constitutes one of the most challenging issues in environmental research because there are still technical and analytical limitations that prevent its correct monitoring. Therefore, conducting studies on PM are of paramount importance to fill the existing gap, providing useful information to develop effective strategies to improve air quality in this region. The general objective of this thesis is to investigate the levels and chemical composition of atmospheric particulate material present in rural and urban areas of Cuba. More specifically, the work aims to identify the main sources of emission of PM, evaluating its possible effects on air quality and the environment. In the first one it is shown that concentrations of PM10 reached annual averages of 35.4 and 24.8 µg m-3 in the rural and urban sites respectively. The highest concentrations of PM were observed between March and August, coinciding with a strong advection of Saharan dust clouds. The PM10 daily limit (50 µg m-3) established in the Cuban legislation for air quality was exceeded 3 and 8 times in the rural and urban sites, respectively. A source apportionment analysis using Positive Matrix Factorization (PMF) model identified 5 main sources in the studied sites (Saharan intrusions, marine aerosol, combustion, road traffic and cement plant). In the second chapter the content, pattern and sources of lanthanoid elements (La to Lu) in PM10 are investigated. Lanthanoid elements concentrations were distributed unevenly throughout the year, showing higher values in the period between April and August when Saharan dust intrusions are more frequent. Chapter 3 reports on the study of the stable isotope compositions (δ13C and δ15N) of total carbon (TC) and nitrogen (TN) in both PM10 and emissions from potential sources of contamination. δ13C isotope signatures revealed that air quality was degraded by the mixed contributions from two main emitters: combustion of fossil fuel and cement plant and quarries, with this last source impacting more air quality at the urban site. In addition, TN and δ15N values from the urban site demonstrated that nitrogen in PM10 was generated by secondary processes through the formation of (NH4)2SO4 and that the corresponding 15N enrichment is controlled by exchange between gaseous NH3 and particle NH4+ in the (NH4)2SO4 molecule under stoichiometric equilibrium. The fourth research study carried out in this thesis describes exhaustively the major and trace elements analyzed in monthly bulk depositions. Most of the analyzed elements were found in the variation range of those reported in rural environments around the world but the elements V, Ni, As and Sb presented higher levels, typically founded in urban and industrial areas. Application of Principal Components, Multilinear Regression and Cluster statistical analyses led the identification of 5 main sources contributing to bulk deposition: crustal matter (39.5%), marine aerosol (38.2%), combustion processes (6.7%), industries (8.7%) and road traffic (1.4%). In the last chapter, the implications of the results obtained in the air quality and the environment of the studied area are evaluated. It should be noted that the results obtained in this work can contribute to significantly improve the understanding of the properties of aerosols in the atmosphere and the potential impacts of air pollutants on terrestrial and aquatic ecosystems. Moreover, this thesis is a valuable source of information to expand the existing datasets in Cuba, thus providing a very useful information to environmental managers and policy makers to take sound decisions that contribute to improving air quality in Cuba.