PhD Thesis by Sharon Ridolfo

The predoctoral researcher Sharon Ridolfo, from the EGAR group, will defend her thesis on 9th July at 11:00h at Universitat Politecnica de Catalunya (Sala Multimèdia Professor Pedro Vicente del Fraile, Edificio B3 – Campus Nord UPC)

Directors: Fulvio Amato and Xavier Querol

Thesis Committee: Jesús Damián de la Rosa Díaz, Eleonora Simona Cuccia and Xavier Gamisans Noguera

Abstract:
Ultrafine particles (UFP), defined as airborne particulates with an aerodynamic diameter smaller than 100 nm, are of particular concern due to their ability to penetrate deep into the respiratory system and even reach the brain directly via the olfactory bulb, with the potential to cause a wide range of adverse health effects. In response to the growing evidence of health risks associated with UFP, the World Health Organization (WHO) has recently issued ‘Good practice statements’ emphasizing the need to integrate UFP in terms of particle number concentration (PNC) into existing air quality monitoring systems (WHO, 2021). In line with these recommendations, the new European Air Quality Directive (AQD, 2024/2881/EC) requires the monitoring of PNC and particle number size distribution (PNSD) in urban supersites and of PNC in rural supersites and pollution hotspots, including traffic, harbors, airports, and industry, among others (EU, 2024). In this context, the present PhD thesis investigates the concentrations, size, and some chemical patterns and source contributions of UFP in transport environments, including a review of existing literature on PNC-PNSD, as well as experimental studies conducted at an airport, harbor, road traffic and urban background (UB) in Barcelona (NE Spain) and a subway in Valencia (E Spain). The review aimed to assess the instruments used, analyze results, and identify knowledge gaps in PNC-PNSD across transport environments. It highlighted understudied areas needing further investigation and provided key insights for the field campaigns. The findings identified road traffic as the main contributor to PNC in urban areas, with commuting modes influenced by proximity to traffic and meteorological conditions. It also emphasized the need for harmonizing measurement protocols due to significant variations in methods, particularly in lower (finer) particle size detection limits. The experimental studies revealed substantial variability in PNC and PNSD, driven by differences in emission sources and site-specific conditions. The airport recorded the highest PNC, dominated by aircraft activity, particularly taxiing and takeoff, while the subway exhibited the lowest. Nucleation mode particles (<25 nm) were especially elevated at the airport and road traffic site, indicating the influence of fresh emissions and secondary formation from gaseous precursors. In contrast, the harbor showed a dominant Aitken mode (25-100 nm) linked to ship emissions. Diurnal trends further reflected localized source activity, with distinct peaks observed in line with transport operations, except in the subway, where PNC remained relatively stable. PNSD was unimodal below 20 nm at the airport and traffic sites, unimodal around 20-30 nm at the harbor, and flatter at the subway, suggesting a lack of significant local sources of UFP. Notably, no second mode (40-90 nm), commonly associated with diesel emissions, was observed at the road traffic site, indicating a possible decline in larger diesel-related particles due to the implementation of EURO 5 and 6/V and VI standards and the Barcelona Low Emission Zone (LEZ). Source apportionment analyses confirmed aviation and shipping as dominant contributors to UFP at the airport and harbor, respectively, while chemical characterization revealed specific racers such as aluminum (airport), chromium and barium (traffic), vanadium and nickel (harbor), and copper (subway), among others.