Chemical Composition, Optical Properties and Sources of PM2.5 From a Highly Urbanized Region in Northeastern Mexico

• Published in: Frontiers in environmental science 2022-07, Vol.10
• Main Authors: Acuña Askar, Karim, González, Lucy T., Mendoza, Alberto, Kharissova, Oxana V., Rodríguez-Garza, Andrea, Lara, Eleazar M., Campos, Alfredo, López-Serna, D., Bautista-Carrillo, Lilia M., Alfaro-Barbosa, J. M., Longoria-Rodríguez, F. E.
• Format: Article
• Language: English
• Subjects: mass absorption efficiency (MAE); parallel factor analysis (PARAFAC); PM2.5; water-soluble organic carbon (WSOC); Ångström absorption exponent
• ISSN: 2296-665X; 2296-665X
• DOI: 10.3389/fenvs.2022.929449

Here, we report the chemical composition and optical properties of the fine particles (PM 2.5 ) and water-soluble organic carbon (WSOC) of these particles. Additionally, the potential sources of WSOC emission were determined through the study on fluorescence excitation–emission matrix spectra and parallel factor analysis (EEM-PARAFAC). Samples were collected in an urban site of the Monterrey Metropolitan Area in Mexico during summer and winter and characterized using attenuated total reflectance-Fourier-transform infrared spectroscopy (ATR-FTIR), ultraviolet-visible-near infrared-diffuse reflectance spectroscopy (UV–Vis-NIR-DRS), fluorescence spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) techniques. The ATR-FTIR analyses allowed the identification of inorganic ions (e.g., CO 3 2− , SO 4 2− , and NO 3 − ), organic functional groups [e.g., carbonyls (C=O), organic hydroxyl (C-OH), carboxylic acid (COOH)], and aromatic and unsaturated aliphatic hydrocarbons. The results obtained by XRD and XPS revealed the presence of organic and inorganic chemical species in PM 2.5 . The diffuse reflectance spectra of PM 2.5 provided the absorption bands in the UV region for CaSO 4 , CaCO 3 , and aluminosilicates. The absorption coefficient at 365 nm (Abs 365 ) and Ångström absorption exponent (AAE) values obtained for the aqueous extracts suggest that many of the water-soluble organic compounds corresponded to brown carbon (BrC) chromophores. The mass absorption efficiency values at 365 nm (MAE 365 ) were higher in the winter than summer samples, suggesting the presence of more BrC compounds in the winter samples. The fluorescence indices combined with EEM-PARAFAC analysis showed that the WSOC fraction was mainly composed of humic-like substances (HULIS) which are both of terrestrial and microbial origin.