Ultrafine Aerosol Particle Sizer Based on Piezoresistive Microcantilever Resonators with Integrated Air-Flow Channel

To monitor airborne nano-sized particles (NPs), a single-chip differential mobility particle sizer (DMPS) based on resonant micro cantilevers in defined micro-fluidic channels (µFCs) is introduced. A size bin of the positive-charged fraction of particles herein is separated from the air stream by aligning their trajectories onto the cantilever under the action of a perpendicular electrostatic field of variable strength. We use previously described µFCs and piezoresistive micro cantilevers (PMCs) of 16 ng mass fabricated using micro electro mechanical system (MEMS) technology, which offer a limit of detection of captured particle mass of 0.26 pg and a minimum detectable particulate mass concentration in air of 0.75 µg/m3. Mobility sizing in 4 bins of a nebulized carbon aerosol NPs is demonstrated based on finite element modelling (FEM) combined with a-priori knowledge of particle charge state. Good agreement of better than 14% of mass concentration is observed in a chamber test for the novel MEMS-DMPS vs. a simultaneously operated standard fast mobility particle sizer (FMPS) as reference instrument. Refreshing of polluted cantilevers is feasible without de-mounting the sensor chip from its package by multiply purging them alternately in acetone steam and clean air

Assessment of portable and miniaturized sensors for the monitoring of human exposure to air pollutants

In the last years, several in-field campaigns have been conducted using portable and miniaturized monitors to evaluate the personal exposure to different pollutants. In general, this kind of monitors are characterized by worse metrological performance if compared to the traditional standard methods. Despite this disadvantage, portable and miniaturized monitors could be easily used across different applications, because their advantageous features, such as the capability to provide real-time measurement, the high spatial and temporal resolution of acquired data, the ability to adapt to different experimental designs and, especially, the ability to follow the subject in any activity. Finally, portable and miniaturized instruments can provide data acquired in the respiratory zone of the subject, following therefore the practices for a correct exposure assessment. Obviously, the best compromise between the analytical gold standard (in terms of precision, accuracy and instrumental sensitivity) and the gold standard in regard to the exposure assessment should be chosen. Therefore, in brief, principal aims of this thesis are (i) to evaluate the on-field performances of portable and miniaturized monitors for gaseous pollutants and airborne PM and (ii) to use these monitors in exposure assessment studies and (iii) to understand if data acquired via portable and miniaturized monitors could be useful in other fields of application, such as epidemiological studies or toxicological studies, in which the evaluation of the inhaled dose of pollutants could play a key role

Particle Sensor Using Solidly Mounted Resonators

This paper describes the development of a novel particle sensing system employing zinc oxide based solidly mounted resonator (SMR) devices for the detection of airborne fine particles (i.e., PM2.5 and PM10). The system operates in a dual configuration in which two SMR devices are driven by Colpitts-type oscillators in a differential mode. Particles are detected by the frequency shift caused by the mass of particles present on one resonator with while the other acts as a reference channel. Experimental validation of the system was performed inside an environmental chamber using a dust generator with the particles of known size and concentration. A sensor sensitivity of 4.6 Hz per μg/m3 was demonstrated for the SMRs resonating at a frequency of 970 MHz. Our results demonstrate that the SMR-based system has the potential to be implemented in CMOS technology as a low-cost, miniature smart particle detector for the real-time monitoring of airborne particles

Étude magnétique des particules en suspension dans l'air (PM) capturées dans des bio-capteurs et des filtres à air dans différents environnements urbains

Les particules en suspension dans l'air (PM) sont aujourd'hui considérées comme un risque majeur pour la santé. Les enfants constituent l'un des groupes les plus vulnérables aux PM et à la pollution atmosphérique. Comme la majorité de la population passe plus de temps à l'intérieur, il est très important de connaître les différentes sources de particules dans cet environnement et la contribution des sources extérieures. Malgré les progrès réalisés dans la compréhension de la qualité de l'air intérieur, de nombreuses lacunes subsistent en ce qui concerne le transfert des particules de l'extérieur vers l'intérieur. Le magnétisme environnemental offre une grande opportunité pour l'étude des PM, car il est suffisamment sensible pour étudier les fractions les plus fines des oxydes de fer présents dans les PM. Les méthodes magnétiques sont également particulièrement adaptées pour être utilisées avec des biocollecteurs, échantillons naturels capables de retenir les polluants. Les biocollecteurs constituent une excellente alternative aux capteurs à faible coût, car ils sont rentables et ont un faible impact sur l'environnement. Ici, nous avons combiné des méthodes magnétiques avec des biocollecteurs afin de mieux comprendre le problème des PM intérieur-extérieur dans différents contextes urbains. L'objectif principal de la thèse était de caractériser les émissions anthropiques de PM à l'intérieur et à l'extérieur et la relation entre elles. Les différentes sources d'émissions urbaines ont été caractérisées dans des filtres PM2.5, fournissant des informations sur les propriétés magnétiques de ces sources, qui ont ensuite été utilisées dans l'étude des biocollecteurs. Les biocollecteurs ont été utilisés dans le cadre de projets scientifiques citoyens, afin d'étudier les PM dans les environnements urbains. Dans cette thèse, des techniques magnétiques innovantes ont également été utilisées pour étudier la fraction ultrafine des PM magnétiques. La microscopie électronique à balayage a fourni des informations morphologiques complémentaires sur les oxydes de fer et les autres constituants des PM. Les résultats indiquent tout d'abord que les différentes sources d'émissions anthropiques présentaient une distribution granulométrique étroite. Pour la ville de Toulouse, les émissions dues au trafic routier ont dominé la fraction magnétique des PM qui sont transportées à l'intérieur des habitations. Des sphérules d'oxydes de fer ultrafines d'environ 50 nm (et plus) liées aux émissions du trafic, ont été détectées au MEB. L'environnement intérieur présente une concentration plus faible de PM magnétiques (avec des I/O moyens pour le SIRM compris entre 0,7 et 0,9 pour les écoles et de 0,5 pour les résidences). La fraction granulométrique est plus fine par rapport à l'extérieur (dans le SSD). La fraction ultrafine pour ce type de grain a un diamètre moyen calculé à 7.7nm. D'autres sources de particules, outre les émissions du trafic, sont également importantes à l'intérieur, notamment dans l'environnement scolaire, comme le montrent les I/O pour la concentration de carbone organique allant de 1,1 à 1,9. Avec l'hypothèse que certaines des particules PM émises en milieu urbain sont entraînées dans le cycle de l'eau, les sédiments de la Garonne ont été étudiés. Les résultats montrent des pics de susceptibilité magnétique (atteignant des valeurs de 2,95x10-6) et de métaux traces (tels que Cu et Pb atteignant des concentrations de 139,0 et 73,5 ppm) dans le centre-ville de Toulouse qui indiquent un apport anthropique. La présence de sphérules d'oxydes de fer de taille micrométrique (allant de 10 à 91 um) montre que les sources d'émission liée au trafic routier sont à l'origine des particules détectées. En conclusion, cette thèse a fourni de nouvelles informations sur les émissions anthropiques de particules et sur leur relation intérieur-extérieur, qui peuvent être utilisées pour caractériser la qualité de l'air dans les environnements urbaines.Airborne particulate matter (PM) is understood nowadays as a major health risk. The finer PM fraction is the most dangerous for human health. Children are one of the most vulnerable groups to PM and air pollution, due to their immature respiratory systems and higher respiration rates than adults. Since the majority of the population spends more time indoors, knowing the different sources of PM in this environment and the contribution of outdoor sources is of great importance. Despite advances in the comprehension of indoor air quality, many gaps still exist regarding PM transfer from outdoors to indoors environments. Environmental magnetism offers a great opportunity for PM investigation, being sensible enough to investigate the finer fractions (sub-micrometric) of iron oxides present in PM even when they occur in small concentrations. Magnetic methods are also particularly suited to be used together with biocollectors, which are natural samples able to retain pollutants, such as tree leaves and tree bark. Biocollectors are a great alternative to low cost sensors, being cost-effective and of low environmental impact. They also offer the opportunity for innovative experimental designs. Here we combined magnetic methods with biocollectors in order to better understand the indoor-outdoor PM problem in different urban contexts. The main goal of the thesis was to characterize anthropogenic emissions of PM indoors and outdoors and the relationship between them. The different urban emission sources were characterized in PM2.5 filters, providing information about the magnetic properties of those sources, which were later used in the study of biocollectors. Biocollectors were used in citizen science projects, to study PM indoors and outdoors in urban environments. In this thesis innovative magnetic techniques were also used to investigate the ultrafine fraction of magnetic PM, regarding grains on the superparamagnetic size range (i.e. below ~30 nm for magnetite). Scanning electronic microscopy provided complementary morphological information about iron oxides and other PM constituents. The results indicate firstly that different anthropogenic emission sources had a narrow grain size distribution. Traffic emissions dominated the magnetic fraction of PM that is carried indoors both in domestic environments and in schools.. Ultrafine iron oxides spherules of about 50 nm (and finer) are related to traffic emissions, as detected in the SEM. The indoor environment has a lower concentration of magnetic PM (with mean I/O for SIRM calculated at 0.7 and 0.9 on the schools and 0.5 on the residencies), although the size fraction is finer in comparison with outdoors (in the SSD). The ultrafine fraction (below the SP-SSD boundary) shows an I/O for concentration calculated at 0.4, evincing a higher concentration outdoors for this kind of grain with mean diameter calculated at 7.7nm. Other PM sources, besides traffic emissions, are also important indoors, especially in the school environment, as shown by I/O for organic carbon concentration ranging from 1.1 to 1.9. Lastly, we investigated the fate of PM emitted in the urban setting. With the hypothesis that PM particles emitted in urban settings are carried away in the water cycle, sediments of the Garonne river were studied. The results show peaks in magnetic susceptibility (reaching values of 2.95x10-6) and trace metals (such as Cu and Pb reaching concentrations of 139.0 and 73.5ppm) in the downtown region of Toulouse that point to anthropogenic input. Presence of iron oxides spherules with micrometric size (ranging from 10 to 91um) shows traffic emission sources as origin for the detected particles. Overall, this thesis provided new insights on the anthropogenic emission of PM, and their indoor-outdoor relationship which can be used in characterizing the domestic and school environment air quality