Air pollution is a major public health concern causing annually an estimated 380000 premature deaths in the European Union alone. A number of epidemiological studies carried out during recent decades have associated atmospheric particulate matter (PM) with cardiovascular and respiratory morbidity and mortality. Thus, investigation of the sources and mechanisms responsible for increasing PM concentrations in urban environments has become one of the most important fields of research in environmental sciences._x000D_ The sources, dispersion and chemical processes governing air quality vary in each European region, so that, for example conclusions regarding atmospheric particle contamination reported for central and northern European cities cannot necessarily be directly applied to the Mediterranean area, where information on the number and size distribution of particles and chemical speciation PM data are relatively scarce. In this context, the study presented in this thesis offers an unprecedentedly detailed investigation of the processes and sources affecting atmospheric pollutants at an urban background site in the coastal Mediterranean city of Barcelona._x000D_ Road traffic is the most important particle source in Barcelona, with exhaust emissions representing about 40-45% of the PM1 mass. It governs the time variation of Black Carbon (BC) levels, which may be proposed as a vehicle exhaust emissions tracer to be added to urban air quality control networks. Study of the BC/CO, BC/NO2 and BC/NO ratios in different European urban environments evidenced the variability of these ratios as a function of the specific characteristic of each site, such as the distance to traffic, vehicle fleet composition and age and the influence of other carbonaceous sources, such as biomass burning._x000D_ The evaluation of the coarse aerosol (PM2.5-10) daily cycle during an intensive sampling campaign (DAURE) evidenced the influence of construction-demolition works. These activities increased hourly PM2.5-10 levels by up to 8 µg m-3 on an annual mean basis based on hourly averages. Although the mineral matter content of this source is similar to traffic resuspension, regional dust or Saharan dust, and it was therefore not possible to discriminate construction/demolition particles in a distinct way, the time variation of coarse Ca and S (tracers of construction works), allowed us to demonstrate the impact of these activities on the PM coarse fraction in our measurements._x000D_ Particle number (N) data were analysed during the DAURE campaign in search for the primary emissions of vehicle exhaust (N1) and the secondary particles from gaseous precursors, primary particles from non-traffic sources, and/or particles inherited in the air mass (N2). This analysis was based on the relation between N and BC. The N2 fraction accounted for 40% of number concentrations, ranging from 37% during the morning rush hour to 61% at midday. This high contribution of N2 during midday prompted us to carry out further analysis using data collected during the whole of 2009, comparing the results in Barcelona with those collected in five other European cities in different regions. This study allowed us to conclude that the midday N peak was only observed in southern European cities, which at that time of day is controlled by: 1) higher solar radiation, 2) higher temperature and 3) a contribution of SO2 from shipping and industry governed by the breeze circulation, all of this resulting in enhanced nucleation processes at these latitudes, giving rise to high particle number concentrations._x000D_ The significant contribution of secondary inorganic aerosols to PMx mass detected in Barcelona, higher than in other European cities with similar NOx and SO2 levels, motivated a study of the levels and sources of NH3, the main precursor of these new formed particles. Passive samplers were used in order to cover a large area of the city in summer and winter, proving higher levels during summer. During this season levels were well above those reported in other European cities. Waste containers were found to be the main source responsible for the high levels, although an important local contribution from traffic emissions was also detected._x000D_ The highest NH3 levels were mostly registered in the historic city centre, which is located to the south of the monitoring site, in an area closest to the sea from where the wind typically transports pollutants at midday. This transport of NH3, the main precursor of particles through reactions with sulphuric and nitric acids, could also partly explain the N midday peak associated with secondary inorganic aerosol formation._x000D_ An annual contribution from regional-scale biomass burning emissions was detected and quantified for the fist time in Barcelona by means of specific tracers, namely Levoglucosan, K+ and OC, and the application of a special-purpose Multilinear Engine-2 (ME-2) script. It results in a contribution of 3% to PM10 and PM2.5 and 5% to PM1, much lower than those calculated for other northern and central European cities. A regional-scale origin of this contribution was concluded, as it showed a characteristic hourly trend with night-time maxima, coinciding with the land-to-sea breeze._x000D_ Finally, the study was broadened to evaluate the exposure risk and toxicology of PM2.5-10 and PM0.1-2.5 using a multidisciplinary approach to obtain an estimation of the health impact of the different emission sources of Barcelona. Two different tests were performed to characterise the oxidative stress generation capacity of the samples, obtaining similar results than those reported in other urban sites with intense metal emissions. Results concerning the ROS-generation capacity were correlated with the ones obtained from a cancer risk assessment of the different PM sources detected in Barcelona by means of the receptor model Positive Matrix Factorization (PMF) and a ME-2 script, attaining a high correlation factor for the PM0.1-2.5 particles. This health risk estimation underestimated the impact of road traffic since only the particulate phase of urban emissions was considered, with the lack of VOCs measurements, which are expected greatly to increase the cancer risk of the exhaust emissions. Finally, four months of on-line measurements of the lung deposited surface area (LDSA) revealed a high correlation factor between this parameter and BC, pointing at traffic as the major factor responsible for daily variation of LDSA in the city of Barcelona.
| Date of Award | 5 Jul 2012 |
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| Original language | English |
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| Supervisor | Mª del Mar Viana Rodriguez (Director) & Teresa Moreno Pérez (Director) |
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