Characterisation and calibration of optical counters for airborne particulate matter

Gli aerosol, sospensione colloidale in aria di particelle solide o liquide, sono parte integrante dell’atmosfera. Essi interagiscono con la radiazione solare influenzando il clima (effetto primario e secondario) e la visibilità atmosferica. Gli aerosol hanno effetti sulla salute umana con patologie degli apparati cardiovascolare e circolatorio. La presente tesi affronta alcuni aspetti critici dei contatori ottici di particelle (OPC), utilizzati per caratterizzare l’aerosol ambientale. Gli OPC si basano sullo scattering luminoso per fornire la concentrazione in numero e la distribuzione dimensionale degli aerosol in tempo reale. Gli obiettivi di questa tesi sono: 1)caratterizzare e migliorare le prestazioni di un OPC di nuova concezione (CompactOPC N1, Alphasense; in seguito COPC) rispetto a un OPC standard commerciale (Grimm 1.108; in seguito GRM); 2)realizzare un banco di prova per la calibrazione di un OPC utilizzato in camere bianche e ambienti sanitari (Laser Particle Sensor 3715-00, Kanomax; in seguito LPS). Per questa attività ha mostrato interesse un’azienda locale (Pollution Clean Air Systems S.p.A.; Budrio, BO). Le prove sperimentali sono state effettuate con aerosol indoor e con particelle monodisperse di latex polistirene (PSL) di dimensioni differenti campionando in parallelo con i diversi OPC e su filtro per osservazioni al microscopio elettronico a scansione (SEM). In questo modo si è ottenuto un valore assoluto di riferimento per la concentrazione di aerosol. I risultati ottenuti indicano un buon accordo tra le concentrazioni di particelle fornite dal GRM e quelle ottenute al SEM. Il lavoro ha inoltre permesso di migliorare le prestazioni del COPC modificando la versione di base. Inoltre, è stata effettuata la calibrazione del LPS tramite il banco di prova realizzato nella tesi. Il lavoro sperimentale è stato svolto presso il Laboratorio di Aerosol e Fisica delle Nubi dell’Istituto di Scienze dell’Atmosfera e del Clima (ISAC) del Consiglio Nazionale delle Ricerche (CNR) a Bologna.

Accelerated ageing methodologies for the evaluation of particulate matter role in the corrosion of outdoor-exposed bronzes

Deterioration phenomena occurring on outdoor cultural heritage have been the subject of several studies, but relatively few works investigated the specific role of Particulate Matter (PM) in the corrosion of metals. This topic is really complex and, besides field exposures, accelerated ageing tests are also necessary to isolate and understand deterioration mechanisms due to PM. For this reason, the development of a methodology that allows to reproduce and analyze the effect of PM on alloys through accelerated ageing in climatic chamber has been started. On quaternary bronze specimens, single salts and a mix of them were deposited via two deposition methods: dry (directly depositing the salt on the surface) and wet (dropping a salt solution and drying it), simulating the initial chemical activation of the salts by RH% variations or by raindrops, respectively. Then, to better mimic the composition of real PM, a mixture containing a soluble salts, a mineral, a black carbon and an organic fraction was formulated and spread on the samples. The samples were placed in a climatic chamber and exposed to cyclic variations of T and RH for three weeks. The ageing cycles were set according to predictions on salt deliquescence/recrystallization through E-AIM model and to the evaluation of regional climatic data. The surface evolution was followed by SEM-EDX, Raman, AT-IR and UV-Vis Spectrophotometry. At the end of the test, mass losses were determined and corroded metals removed by pickling were analyzed by AAS. On the basis of the obtained results, the tested procedures seem to be promising in accelerating and mimicking realistic corrosion phenomena, as under the selected conditions, corrosion products typically found at different exposure time (from days to years) on outdoor bronzes were able to progressively form and evolve. Moreover, the two deposition modes simulating different condition of chemical activation of PM deposits allow to obtain complementary information.

PM and material decay: analysis of dry depositions on horizontal and vertical surrogate surfaces through a Deposition Box system

Airborne Particulate Matter (PM), can get removed from the atmosphere through wet and dry mechanisms, and physically/chemically interact with materials and induce premature decay. The effect of dry depositions is a complex issue, especially for outdoor materials, because of the difficulties to collect atmospheric deposits repeatable in terms of mass and homogeneously distributed on the entire investigated substrate. In this work, to overcome these problems by eliminating the variability induced by outdoor removal mechanisms (e.g. winds and rainfalls), a new sampling system called ‘Deposition Box’, was used for PM sampling. Four surrogate materials (Cellulose Acetate, Regenerated Cellulose, Cellulose Nitrate and Aluminum) with different surfaces features were exposed in the urban-marine site of Rimini (Italy), in vertical and horizontal orientations. Homogeneous and reproducible PM deposits were obtained and different analytical techniques (IC, AAS, TOC, VP-SEM-EDX, Vis-Spectrophotometry) were employed to characterize their mass, dimension and composition. Results allowed to discriminate the mechanisms responsible of the dry deposition of atmospheric particles on surfaces with different nature and orientation and to determine which chemical species, and in which amount, tend to preferentially deposit on them. This work demonstrated that “Deposition Box” can represent an affordable tool to study dry deposition fluxes on materials and results obtained will be fundamental in order to extend this kind of exposure to actual building and heritage materials, to investigate the PM contribution in their decay.

Test sperimentali e modellazione di una torre di lavaggio per la filtrazione di particolato sottile in impianti di combustione delle biomasse

This study investigates biomass and particulate matter also known as PM produced from the combustion of a domestic boiler powered by mais and how to separate PM from the stream of smoke output from the boiler using wet scrubber with structured packing. Sperimentations show the inefficiency of the separator used, so we provide an optimization of the structured packing changing geometric parameters as angle of the bend or thickness of the channels. In order to obtain a higher separation efficiency we remove the structured packinkg and introduce a packed bed composed of spheres of polyethylene with a diameter of 3 mm.