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Hourly Measurements of Organic Aerosol Chemical Species (TAG-GC-MS) at a Receptor Site in Mexico City
Y. MARGARITA MARTÍNEZ-DOMÍNGUEZ, Armando Retama-Hernández, Olivia Rivera-Hernández, Tania Müller-García, Omar Amador-Muñoz, Atmospheric Science Center, UNAM
Abstract Number: 88
Working Group: Urban Aerosols
Abstract
The determination of specific compounds of the Organic Aerosol (OA) provides information on emission sources and secondary organic chemical species formation. In this work, the organic chemical composition analysis of the particles ≤2.5 µm (PM2.5) with hourly time resolution was carried out using a Thermal desorption Aerosol coupled to a Gas Chromatograph - Mass Spectrometer (TAG-GC-MS). The sampling campaign was carried out from November 5 to December 15, 2018 at southwest of Mexico City, considered as a receptor site. The analysis included 82 compounds grouped into: polycyclic aromatic hydrocarbons (PAH), oxy-PAH, n-alkanes, phthalates, and aldehydes. Its diurnal/nocturnal variations showed characteristic features that represent the corresponding activities of the emission sources. PAH were emitted from vehicular sources, except retene, a PAH originated from biomass burning observed throughout the season. Oxy-PAHs were emitted by mobile sources (benzanthrone) and formed overnight (anthraquinone). Phthalates were emitted by sources associated with plastic industrial activities, except for dicyclo-hexyl-phthalate, which apparently was originated from mobile sources. Aldehydes showed both primary origin and secondary formation, where n-alkanes <C23 apparently act as precursors of their formation via OH free radicals during the day. The origin of n-alkanes was both, petrogenic and biogenic. n-alkanes <C23 (petrogenic) were abundant during the day, while n-alkanes ≥C23 (mainly biogenic) were abundant during the night.
n-alkanes contributed with 71% on average of the total mass of all determined species, aldehydes contributed with 13%, phthalates with 10%, PAHs with 4% and oxy-PAHs with 2%. The total amount of all found species contributed only ~0.2% of the total PM2.5 mass, highlighting the particle complexity. PM2.5 mass concentration was quite constant between December and November; however, 2-3 times higher PAH and oxy-PAH levels were observed in December respect to November, which marks a differential in the toxicity of the particles. Acknowledgments: Financial support: Environmental Ministry (SEDEMA) of Mexico City Government, PAPIIT IN102519, UC MEXUS-CONACyT CN-1987.