Ultrafine Particle Levels Monitored at Different Transport Modes in Lisbon

Ultrafine particles (UFP) are defined as particulate matter with a diameter smaller than 0.1 μm. Because of their reduced size and consequently very low mass, they are usually expressed in particle number concentration (PNC), in particles per cubic centimetre (pt.cm-3). There have been growing evidences that long-term exposure to UFP may induce or aggravate pulmonary and cardio-respiratory health conditions and are linked to increased hospitalization and mortality rates. More recently, they have also been linked to neurological diseases and to children cognitive development issues. Airports, road traffic and maritime transport have been identified as significant sources of ultrafine particulate matter. There is lack of information regarding PNC in the vicinity of airports. In the case of Lisbon Airport (LA), located within the city and surrounded by housing areas, offices, schools, hospitals and sport and recreational complexes, knowing their levels assumes vital relevance. In-land passenger ferries are also a source of UFP, far less addressed. A significant fraction of a person's total daily exposure to fine and ultrafine particles occurs during home-work commuting periods. Therefore, microenvironments influenced by different transport modes are particularly relevant. Thus, to associate their contribution with to UFP concentrations is important and allows the estimation of their contribution to air quality degradation within the city and the degree of population exposure. This work aims to assess the effect on UFP concentrations from road, air and river traffic modes, in Lisbon. UFP monitoring campaigns were carried out between July 2017 and December 2018, for a 36 nonconsecutive days period, complying approximately 160 hours of suitable measurements. Concerning road traffic, three sites were chosen with different traffic patterns, vehicle circulation, legal restrictions and different flow intensity of pedestrians close-by. Regarding air traffic, the monitoring network was designed to include several sampling sites in the vicinity of LA and a set of sites further away, under the landing and take-off path. Finally, to assess the in-land ferries-related UFP levels, the sampling sites were chosen in order to maximize measurements under downwind conditions and allow the association between ferry operations and PNC response. Based on the information collected, the obtained levels were analysed and several statistical analysis were performed, particularly searching for correlations between UFP concentrations and the three different traffic activity modes. Concerning road traffic, in Av. da Liberdade, results show high peak values of 1-minute PNC mean (up to 75 x 103 pt.cm-3). This avenue (downtown, in the most striker Low Emission Zone (LEZ1)) presents the higher PNC levels and dispersion (18.2 ± 13.2 x 103 pt.cm-3) followed by a highspeed road (2nd Circular, 15.0 ± 12.2 x 103 pt.cm-3). The lowest values were found at an interception close to LEZ2 boundary (Entrecampos, 10.3 ± 5.1 x 103 pt.cm-3). Moreover, the results of analysis of variance (ANOVA) show that PNC levels are statistically different among the sampled locations. Results suggest that PNC are strongly dependent on the type and age of vehicles: light-duty vehicles, taxis and buses. PNC peak values were mainly associated with vehicles prior to the Euro 3/III Standard. Finally, results show a strong positive correlation, statistically significant, between hourly mean values of PNC and PM10 (r = 0.76, p < 0.01) and a moderate positive correlation between PNC and nitrogen oxides (r coefficients of 0.55, 0.51 and 0.59, with all p-values lower than 0.01, for NO, NO2: and NOx, respectively). Regarding air traffic, results show the occurrence of high UFP concentrations in LA vicinity. Considering 10-minutes means, the particle counting increases by 18 to 26-fold at downwind locations near the airport, and by 4-fold at locations up to 1 km distance to LA. Results show that particle number increases with the number of flights and decreases with the distance to LA. Finally, concerning ferries, data show that UFP emitted contributes to PNC increase in the surrounding area. Results show an increase in PNC, ranging from 25 to 197% during the third minute before an arrival or departure of a ship, with moderate to positive correlations, statistically significant, between PNC values and the number of ferry operations (r = 0.79 to r = 0.94). Moreover, negative correlations (r = -0.85 to r = -0.93) between PNC and wind intensity were also found. This work, based on Lisbon study-case, show that people working, living or spending a considerable amount of time close to intense traffic roads, nearby the airport or close to ferries’ stations or downwind to their cruising path are exposed to high UFP concentrations with a magnitude which may lead to considerable health risks.