Title: Volatile Organic Compounds in the Planetary Boundary Layer: Sources, Accumulation and Vertical Distribution
The predoctoral researcher Isabel Díez Palet, from the Geochemistry and Pollution group, will defend her thesis on 10th December at 11:30h in Sala de Graus Eduard Fontseré, Facultat de Química, Universitat de Barcelona.
Directors: Joan O. Grimalt and Pilar Fernández
Thesis Committee: Rosa Maria Marcé Recasens, Ana María Yáñez-Serrano and Eva Gallego Piñol
Abstract:
Volatile organic compounds (VOCs) are emitted from diverse sources. Some are carcinogenic (e.g., benzene), others neurotoxic (e.g., toluene), and many act as precursors of tropospheric ozone and secondary organic aerosol (SOA). This PhD thesis investigated the origins, composition, and transformation of VOCs across rural, suburban, and industrial sites in the Western Mediterranean.
By developing a new sampling methodology using tethered balloons, ground-level measurements were combined with vertical profiles up to 400 m AGL. This approach allowed sampling of VOCs both below and above the nocturnal residual layer.
Results showed anthropogenic activities as the dominant drivers of VOC variability, with meteorology and seasonality exerting secondary influences. Summer heat enhanced biogenic isoprene and evaporation of anthropogenic VOCs, while winter inversions favored accumulation of traffic- and biomass-related emissions.
Importantly, a small set of anthropogenic VOCs was found to control oxidative capacity, ozone formation, and SOA production, with biogenic contributions becoming more relevant in summer.
Vertical profiles revealed that local VOC emissions and photooxidation influence VOC composition up to 350 m. Primary compounds accumulated near the surface, while secondary products and long-lived VOCs were more evenly distributed. Aloft, air masses were systematically more oxidized than near the surface, particularly in winter and in the nocturnal residual layer, and showed greater accumulation of long-lived VOCs and secondary products.
Because the oxidative state of the residual layer may have an impact on surface air quality the following day, these findings may help to fill existing gaps on VOC and secondary pollution formation, providing new insights for improving atmospheric models and consequently for assessing the environmental impact of VOC pollution in the low troposphere.
