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.

Constraining FIR size, dust temperature and dust mass in ALPINE galaxies at redshift 4

The study of galaxies at high redshift plays a crucial role to understand the mechanism of galaxy formation and evolution. At redshifts just after the epoch of re-ionization (4emission in high-redshift galaxies and to provide a lower limit on dust temperature, to constrain the dust mass. This is achieved by studying 23 FIR continuum detected main-sequence galaxies of the ALMA Large Program to INvestigate (ALPINE) survey, performed at high redshift (4emission, i.e. the dust size, with the stellar and gas distribution, traced by the UV and [CII] emission, respectively. Finally, we put these results in a broader context, by studying the dust size evolution as a function of cosmic time. We derive dust size measurements via a Gaussian fit in the image and uv plane. Out of the 23 FIR-continuum-detected targets, 20 have been considered in this work since they are isolated systems. Of these 20, 7 are spatially resolved; for each of the remaining 13, we provide an upper limit to the dust size. We find that the gas emission is more extended than the dust spatial scale, by a factor of 1.40±0.29, while the latter appears to be larger than the stellar emission size. Moreover, we do not find any significant trend for dust size as a function of the stellar mass and the redshift. In addition, we provide a minimum dust temperature estimate for the 7 resolved sources, for which we find Tmin∼16−19K. We also derive dust masses for the resolved sources, logMdust∼7−8M⊙.