Airborne particle emission of a commercial 3D printer: the effect of filament material and printing temperature.

The knowledge of exposure to the airborne particle emitted from three-dimensional (3D) printing activities is becoming a crucial issue due to the relevant spreading of such devices in recent years. To this end, a low-cost desktop 3D printer based on fused deposition modeling (FDM) principle was used. Particle number, alveolar-deposited surface area, and mass concentrations were measured continuously during printing processes to evaluate particle emission rates (ERs) and factors. Particle number distribution measurements were also performed to characterize the size of the emitted particles. Ten different materials and different extrusion temperatures were considered in the survey. Results showed that all the investigated materials emit particles in the ultrafine range (with a mode in the 10-30-nm range), whereas no emission of super-micron particles was detected for all the materials under investigation. The emission was affected strongly by the extrusion temperature. In fact, the ERs increase as the extrusion temperature increases. Emission rates up to 1×1012  particles min-1 were calculated. Such high ERs were estimated to cause large alveolar surface area dose in workers when 3D activities run. In fact, a 40-min-long 3D printing was found to cause doses up to 200 mm2 .

Ultrafine particle emission from incinerators: the role of the fabric filter.

Incinerators are claimed to be responsible of particle and gaseous emissions: to this purpose Best Available Techniques (BAT) are used in the flue-gas treatment sections leading to pollutant emission lower than established threshold limit values. As regard particle emission, only a mass-based threshold limit is required by the regulatory authorities. However; in the last years the attention of medical experts moved from coarse and fine particles towards ultrafine particles (UFPs; diameter less than 0.1 microm), mainly emitted by combustion processes. According to toxicological and epidemiological studies, ultrafine particles could represent a risk for health and environment. Therefore, it is necessary to quantify particle emissions from incinerators also to perform an exposure assessment for the human populations living in their surrounding areas. A further topic to be stressed in the UFP emission from incinerators is the particle filtration efficiency as function of different flue-gas treatment sections. In fact, it could be somehow important to know which particle filtration method is able to assure high abatement efficiency also in terms of UFPs. To this purpose, in the present work experimental results in terms of ultrafine particle emissions from several incineration plants are reported. Experimental campaigns were carried out in the period 2007-2010 by measuring UFP number distributions and total concentrations at the stack of five plants through condensation particle counters and mobility particle sizer spectrometers. Average total particle number concentrations ranging from 0.4 x 10(3) to 6.0 x 10(3) particles cm(-3) were measured at the stack of the analyzed plants. Further experimental campaigns were performed to characterize particle levels before the fabric filters in two of the analyzed plants in order to deepen their particle reduction effect; particle concentrations higher than 1 x 10(7) particles cm(-3) were measured, leading to filtration efficiency greater than 99.99%.

Effects of the flue gas treatment of incinerator plants on sub-micron particle concentrations at the stack.

The paper is focused on the emission of sub-micron particles from incinerator plants characterized by different treatment sections. In particular, measurement of particle number concentrations and distributions in different sampling points of the flue-gas treatment sections, and/or over several years, allowed to detect, for the very first time through in-field tests, the effect of the age of the fabric filter bags and of the SCR system on the emission of sub-micron particles. In fact, tests showed that the age of the fabric filter bags can affect the particle number concentrations at the stack: indeed, for older bags higher concentrations at the stack were measured likely due to the filter cleaning process. Concerning the effect of the SCR system, the natural gas combustion performed in the SCR system leads to an increase of sub-micron particle concentrations at the stack with respect to the values measured after the filtration section.

A novel approach to evaluate the lung cancer risk of airborne particles emitted in a city.

Air quality still represents a main threat to human health in cities. Even in developed countries, decades of air pollution control not yet allowed to reduce pollutant concentrations in urban areas adequately. Indeed, high airborne particle concentrations are measured in several European cities; this is a main issue since particles represent a carrier for carcinogenic compounds. Numerous researches measuring the exposure to the different aerosol metrics in urban areas were recently performed, nonetheless, few data on the lung cancer risk in such environments are available. In the present paper a novel approach to evaluate the lung cancer risk related to the airborne particles emitted by the different sources located in a city is proposed and applied to a pilot case-study (i.e. an Italian city). In particular, an existing lung cancer risk model was modified and applied to assess the particle-related lung cancer "emitted" by the different sources of the city using pollutant emission factors provided by accredited emission inventory databases. Therefore, the average toxicity of the particles emitted by the city (i.e. lung cancer slope factor) and the lung cancer risk globally emitted by the city, expressed as new cases of lung cancer, were evaluated. The proposed emission inventory also allowed to identify and localize the main contributors to the overall risk emitted in a city. As an example, for the city under investigation, the research revealed that the main contributor, amongst the sources considered, is the vehicular traffic which is characterized by a lower mass fraction of carcinogenic compounds but a much higher sub-micron particle emission with respect to the other sources.

Characterization of airborne particles emitted by an electrically heated tobacco smoking system.

Smoking activities were recognized as a main risk factor for population. Indeed, mainstream smoke aerosol is directly inhaled by smokers then delivering harmful compounds in the deepest regions of the lung. In order to reduce the potential risk of smoking, different nicotine delivery products have been recently developed. The latest device released is an electrically heated tobacco system (iQOS®, Philip Morris) which is able to warm the tobacco with no combustion. In the present paper a dimensional and volatility characterization of iQOS-generated particles was performed through particle number concentration and distribution measurements in the mainstream aerosol. The experimental analysis was carried out through a condensation particle counter, a fast mobility particle sizer and a thermo-dilution sampling system allowing aerosol samplings at different temperatures. Estimates of the particle surface area dose received by smokers were also carried out on the basis of measured data and typical smoking patterns. The particle number concentrations in the mainstream aerosols resulted lower than 1 × 108 part. cm-3 with particle number distribution modes of about 100 nm. Nonetheless, the volatility analysis showed the high amount of volatile fraction of iQOS-generated particles, indeed, samplings performed at 300 °C confirmed a significant particle shrinking phenomena (modes of about 20 nm). Anyway, the particle number concentration does not statistically decrease at higher sampling temperatures, then showing that a non-volatile fraction is always presents in the emitted particles. The dose received by smokers in terms of non-volatile amount of particle surface area was equal to 1-2 mm2 per puff, i.e. up to 4-fold larger than that received by electronic cigarette vapers.

Lung cancer risk assessment due to traffic-generated particles exposure in urban street canyons: A numerical modelling approach.

Combustion-generated nanoparticles are responsible for negative health effects due to their ability to penetrate in the lungs, carrying toxic compounds with them. In urban areas, the coexistence of nanoparticle sources and particular street-building configurations can lead to very high particle exposure levels. In the present paper, an innovative approach for the evaluation of lung cancer incidence in street canyon 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 kind of vehicles were used to calculate the Excess Lifetime Cancer Risk (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, height of 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 min 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.

Particle-related exposure, dose and lung cancer risk of primary school children in two European countries.

Schools represent a critical microenvironment in terms of air quality 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. Air quality-based studies involving students' exposure at schools are still scarce and often limited to mass-based particle metrics and may thus underestimate the possible effect of sub-micron particles and particle toxicity. To this purpose, the present paper aims to evaluate the exposure to different airborne particle metrics (including both sub- and super-micron particles) and attached carcinogenic compounds. Measurements in terms of particle number, lung-deposited surface area, and PM fraction concentrations were measured inside and outside schools in Barcelona (Spain) and Cassino (Italy). Simultaneously, PM samples were collected and chemically analysed to obtain mass fractions of carcinogenic compounds. School time airborne particle doses received by students in classrooms were evaluated as well as their excess lung cancer risk 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 110mm2 and 303mm2, respectively. The risk related to the five-year primary school period was estimated as about 2.9×10-5 and 1.4×10-4 for students of Barcelona and Cassino, respectively. The risk in Barcelona is slightly higher with respect to the maximum tolerable value (10-5, according to the U.S. Environmental Protection Agency), mainly due to toxic compounds on particles generated from anthropogenic emissions (mainly industry). On the other hand, the excess lung cancer risk in Cassino is cause of concern, being one order of magnitude higher than the above-mentioned threshold value due to the presence of biomass burning heating systems and winter thermal inversion that cause larger doses and great amount of toxic compounds on particles.