Exposure to airborne particles: estimation of dose and lung cancer risk of the population living in western countries

In the present thesis, six experimental campaigns were carried out to better understand the influence of the lifestyle in the exposure to airborne particles and to estimate the typical received daily dose of different populations. Moreover, a risk assessment based on an Excess Lung Cancer Risk (ELCR) model was performed taking into account two crucial environments: school environments and street canyons. In addition, an evaluation of the effectiveness of some possible solution to reduce the ELCR was performed taking into account two solution: (i) personal protectors (facemasks) for outdoor environments, and (ii) air purifiers and ventilation strategies for indoor environments. The daily dose in terms of particle surface area received by citizens living in five cities in Western countries (Barcelona, Cassino, Guilford, Lund and Brisbane), characterized by different lifestyle, culture and climate, was evaluated and compared. Non-smoking volunteers performing non-industrial jobs were considered in the study. Particle concentration data allowed obtaining the exposure of the “typical citizen” for each city. Such data were combined in a Monte Carlo method with the time activity pattern data characteristics of each population and inhalation rates to obtain the most probable daily dose in terms of particle surface area as a function of the population gender, age, and nationality. Indoor Air Quality (IAQ), and in particular cooking and eating activities, was recognized as the main influencing factor in terms of exposure (and thus dose) of the population: then confirming that lifestyle (e.g. time spent in cooking activities) strongly affect the daily dose of the population. Looking at outdoor environments/activities, one of the most influencing microenvironments/activity to airborne particle exposure is "transport". To better understand this environment Vehicular Indoor Air Quality (VIAQ) was investigated inside 14 diesel/non-diesel taxi pairs operating simultaneously and under normal working condition over six weekday hours (10:00-16:00) in the city of Barcelona. Parameters measured included PM10 mass and chemistry, particle number concentration (PNC) and size, lung deposited surface area (LDSA), black carbon (BC), CO2, CO, and a range of volatile organic compounds (VOCs). Keeping the windows open or close has shown the dominant influence of the air exchange rates on VIAQ. Median values of PNC and LDSA were reduced to around 104 #/cm3 and <20 µm2/cm3 respectively under closed conditions, but more than doubled with windows open and sometimes approached 105 #cm-3 and 240 µm2/cm3. In urban areas, the coexistence of nanoparticle sources and particular street-building configurations can lead to very high particle exposure levels. An innovative approach for the evaluation of lung cancer incidence in street canyons due to exposure to traffic-generated particles was proposed. To this end, the literature-available values of particulate matter, PAHs and heavy metals emitted from different type of vehicles were used to calculate the ELCR at the tailpipe. The estimated ELCR was then used as input data in a numerical CFD (Computational Fluid Dynamics) model that solves the mass, momentum, turbulence and species transport equations, in order to evaluate the cancer risk in every point of interest inside the street canyon. Thus, the influence of wind speed and street canyon geometry (H/W, the height of the building, H and width of the street, W) on the ELCR at street level was evaluated by means of a CFD simulation. It was found that the ELCR calculated on the leeward and windward sides of the street canyon at a breathable height of 1.5 m, for people exposed 15 minutes per day for 20 years, is equal to 1.5×10-5 and 4.8×10-6, respectively, for wind speed of 1 m/s and H/W equal to 1. The ELCR at street level results higher on the leeward side for aspect ratios equal to 1 and 3, while for aspect ratio equal to 2 it is higher on the windward side. In addition, the simulations showed that with the increasing of wind speed the ELCR becomes lower everywhere in the street canyon, due to the increased in dispersion. Moving the attention on the indoor environments, schools may be classified as a critical microenvironment in terms of IAQ due to the proximity to outdoor particle sources and the frequent lack of proper ventilation and filtering systems. Moreover, the population exposed in schools (i.e. children) represents a susceptible population due to their age. Measurements in terms of PNC, LDSA, and PM fraction concentrations were measured inside and outside schools in Barcelona (Spain) and Cassino (Italy). Simultaneously, PM samples were collected and chemically analyzed to obtain mass fractions of carcinogenic compounds. School time airborne particle doses received by students in classrooms were evaluated as well as their ELCR due to a five-year primary school period. Median surface area dose received by students during school time in Barcelona and Cassino resulted equal to 110 mm2 and 303 mm2, respectively. The risk related to the five-year primary school period was estimated about 2.9×10-5 and 1.4×10-4 for students of Barcelona and Cassino, respectively. Different solutions were taken into account to reduce personal as well as collective exposure to airborne particles. An individual protective measure against particle pollution may be represented by face masks. A custom experimental set-up was developed in order to measure the effectiveness of nine different respirators under real environmental conditions in terms of particle mass concentration below 2.5 microns (PM2.5), PNC, LDSA and BC. Facemask performances were assessed in a typical traffic affected urban background environment in the city of Barcelona under three different simulated breathing rates to investigate the influence of flow rate. Results showed a median face mask effectiveness for PM2.5 equal to 48% in a range of 14-96%, 19% in a range of 6% - 61% for BC, 19% in a range of 4% - 63% for PNC and 22% in a range of 5% - 65% for LDSA. A collective and indoor-adaptable solution to reduce exposure to airborne particles could be represented by air purifiers and ventilation strategies. To evaluate the effect of different ventilation methods (natural ventilation, manual airing) and the use of air purifiers in reducing the indoor concentrations of different airborne particles and gaseous pollutants in indoor environments an experimental campaign was performed. The samplings were carried out in two naturally-ventilated school gyms in Barcelona (Spain) of different volumes and different distance to major urban roads. Indoor and outdoor measurements of PNC, BC and PM1-10 concentrations were performed as well as indoor measurements of CO2 and NO2 concentrations. The study revealed that the use of air purifier with windows kept closed (natural ventilation) can lead to a significant reduction in terms of indoor-to-outdoor concentration ratios. In the smaller gym (air changes per hour of the purifiers, ACH, equal to 9.2 h-1) the I/O ratios were reduced by 93% and 95% in terms of particle number and PM1-10, respectively; whereas in the larger school gym (ACH=1.7 h-1) the corresponding reductions were 70% and 84%. For manual airing scenarios, the effect of the air purifiers on outdoor-generated sub-micron particles is reduced; in particular, for low ACH values (i.e. ACH=1.7 h-1), the reduction is quite negligible (6%).