Two-wavelength thermo-optical determination of Light Absorbing Carbon in atmospheric aerosols

Thermo-optical analysis is widely adopted for the quantitative determination of Total, TC, Organic, OC, and Elemental, EC, Carbon in atmospheric aerosol sampled by suitable filters. Nevertheless, the methodology suffers of several uncertainties and artefacts as the well-known issue of charring affecting the OC-EC separation. In the standard approach, the effect of the possible presence of Brown Carbon, BrC, in the sample is neglected. BrC is a fraction of OC, usually produced by biomass burning with a thermic behaviour intermediate between OC and EC. BrC is optically active: it shows an increasing absorbance when the wavelength moves to the blue/UV region of the electromagnetic spectrum. Definitively, the thermo-optical characterization of carbonaceous aerosol should be reconsidered to address the possible BrC content in the sample under analysis. We introduce here a modified Sunset Lab Inc. EC/OC Analyzer. Starting from a standard commercial set-up, the unit has been modified at the Physics Department of the University of Genoa (IT), making possible the alternative use of the standard laser diode at \u3bb = 635 nm and of a new laser diode at \u3bb = 405 nm. In this way, the optical transmittance through the sample can be monitored at both the wavelengths. Since at shorter wavelengths the BrC absorbance is higher, a better sensitivity to this species is gained. The modified set-up also gives the possibility to quantify the BrC concentration in the sample at both the wavelengths. The new unit has been thoroughly tested, with both artificial and real-world samples: the first experiment, in conjunction with the Multi Wavelength Absorbance Analyzer (MWAA, Massab\uf2 et al., 2013 and 2015), resulted in the first direct determination of the BrC Mass Absorption Coefficient (MAC) at \u3bb = 405 nm: MAC = 23 \ub1 1 m2 g-1

Two-wavelength thermo-optical determination of Organic, Elemental and Brown Carbon.

Introduction Thermo-optical analysis (TOA) is widely adopted for the quantitative determination of Carbonaceous Aerosol in aerosol samples collected on quartz fibre filters. Nevertheless, the quantification of Elemental and Organic Carbon (EC and OC) presents several issues, as the well-known artefacts induced by the formation of pyrolytic carbon (Pyr-C) during the analysis. Furthermore, it is usually neglected the uncertainty due to the possible presence of Brown Carbon (BrC) i.e. the optically active fraction of OC produced by biomass burning and with thermic characteristics intermediate between OC and EC. Methods In (Massab\uf2 et al., 2019), a modified Sunset EC/OC Analyzer was introduced. Briefly, the unit was upgraded making possible the alternative use of a laser diode at \u3bb = 635 nm and at \u3bb = 405 nm. In this way, the optical transmittance through the sample can be monitored at both the wavelengths. Both BrC and Pyr-C absorbance increases at shorter wavelength, so the new set-up has a better sensitivity to these species. First results Massab\uf2 et al., 2019) suggested that the 2-lambda TOA could reduce the discrepancy usually observed between EC/OC quantification by the NIOSH and EUSAAR protocols (Cavalli et al., 2010). Adopting the methodology described in (Massab\uf2 et al., 2016), i.e. the coupled use of the Multi-Wavelength Absorbance Analyzer (MWAA) and of the Sunset EC/OC Analyzer, we therefore performed a new experiment based on a set of samples collected in a rural site. Half of the samples were analysed with the EUSAAR_2 and NIOSH protocols at both the wavelengths looking for OC, EC and BrC concentration values. The other sub-set was instead used to compare the TOA results on untreated and water-washed samples, again using both the laser diodes at \u3bb = 635 nm and \u3bb = 405 nm. The water-wash step removes the water-soluble compounds, which are expected to be the main responsible of the Pyr-C formation in TOA (Piazzalunga P. et al., 2011). Finally, all the samples were also analysed to quantify the Levoglucosan (1,6-Anhydro-betaglucopyranose) content. This step, performed by High Performance Anion Exchange Chromatography coupled with Pulsed Amperometric Detection(HPLC-PAD, more details in Piazzalunga A. et al., 2010), provided the quantification of this biomass burning tracer regardless of BrC thermo-optical properties. The BrC Mass Absorption Cross-section (MAC) at \u3bb = 405 nm and \u3bb = 635 nm was finally determined. Conclusions The data reduction of the described experiment is still in progress: the results will be presented and discussed at the Conference. This work has been partially financed by the National Institute of Nuclear Physics (INFN) in the frame of the TRACCIA experiments. Cavalli, F., Putaud, J. P., Viana, M., Yttri, K. E., & Gemberg, J. (2010). Toward a standardized thermal-optical protocol for measuring atmospheric Organic and Elemental Carbon: the EUSAAR protocol. Atmos. Meas. Tech., 3, 79-89. Massab\uf2, D., Altomari, A., Vernocchi, V., & Prati, P. (2019). Two-wavelength thermo-optical determination of Light Absorbing Carbon in atmospheric aerosols. Atmos. Meas. Tech. Discuss. Massab\uf2, D., Caponi, L., Bove, M. C., & Prati, P. (2016). Brown carbon and thermal-optical analysis: a correction based on optical multiwavelength apportionment of atmospheric aerosols. Atmos. Environ., 125, 119-125. Piazzalunga, A., Fermo, P., Bernardoni, V., Vecchi, R., Valli, G., & De Gregorio M. A. (2010). A simplified method for levoglucosan quantification in wintertime atmospheric particulate matter by high performance anion-exchange chromatography coupled with pulsed amperometric detection. Int. J. Environ. An. Ch., 90, 934-947. Piazzalunga, P., Bernardoni, V., Fermo, P., Valli, G., & Vecchi, R. (2011). On the effect of watersoluble compounds removal on EC quantification by TOT analysis in urban aerosol samples. Atmos. Chem. Phys., 11, 10193-10203

Characterization of soot produced by the mini inverted soot generator with an atmospheric simulation chamber

The performance of a mini inverted soot generator (MISG) has been investigated at ChAMBRe (Chamber for Aerosol Modelling and Bio-aerosol Research) by studying the properties of soot particles generated by ethylene and propane combustion. This work deepens and expands the existing characterization of the MISG, which also exploits an atmospheric simulation chamber (ASC). Different from previous works, MISG performance has been also tested at different fuel flows and higher global equivalence ratios. MISG exhausts were investigated after their injection inside the atmospheric simulation chamber, which is another novelty of this work. Starting from an extensive classification of combustion conditions and resulting flame shapes, the MISG exhaust was characterized in terms of concentration of emitted particles and gases, particle size distribution, and optical properties. Soot particles were also collected on quartz fibre filters and then analysed by optical and thermal\u2013optical techniques to measure the spectral dependence of the absorption coefficient babs and their composition in terms of elemental carbon and organic carbon (EC and OC). Significant differences could be observed when the MISG was fuelled with ethylene and propane in terms of particle size. In particular, the production of super-micrometric aggregates was observed for ethylene combustion. With equal combustion conditions, ethylene produced a higher number concentration of particles and smaller mode diameters. Soot particles produced by propane combustion resulted in higher EC : TC (total carbon) ratios and they were more light absorbing than particles generated by ethylene combustion. Values of the mass absorption cross section (MAC) and of the \uc5ngstr\uf6m absorption exponent (AAE) turned out to be compatible with the literature, even if there were some specific differences. The comprehensive characterization of the MISG soot particles is an important piece of information to design and perform experiments in atmospheric simulation chambers. Particles with well-known properties can be used, for example, to investigate the possible interactions between soot and other atmospheric pollutants, the effects of meteorological variables on soot properties, and the oxidative and toxicological potential of soot particles

Determinazione termo-ottica a pi\uf9 lunghezze d'onda di Elemental, Organic e Brown Carbon

Gli aerosol carboniosi sono largamente presenti in atmosfera ma ancora poco conosciuti. La loro caratterizzazione si basa frequentemente su tecniche termo-ottiche, non esenti da artefatti e sistematici poco compresi. Presentiamo una nuova metodologia basata su uno strumento commerciale (Sunset EC/OC Analyzer) che \ue8 stato modificato rendendo possibile l\u2019analisi a pi\uf9 lunghezze d\u2019onda. Parte integrante dello sviluppo \ue8 un nuovo approccio all\u2019analisi dei dati strumentali. Si ottiene cos\uec una migliore conoscenza delle frazioni in cui viene solitamente diviso l\u2019aerosol carbonioso: Carbonio Elementale (o \u201cBlack\u201d) ed Organico ivi incluso il cosiddetto Brown Carbon, che \ue8 solitamente trascurato nelle analisi termo-ottiche

Comparative characterization of the performance of bio-aerosol nebulizers in connection with atmospheric simulation chambers

The interplay of bio-aerosol dispersion and impact, meteorology, and air quality is gaining increasing interest in the wide spectrum of atmospheric sciences. Experiments conducted inside confined artificial environments, such as atmospheric simulation chambers (ASCs), where atmospheric conditions and composition are controlled, can provide valuable information on bio-aerosol viability, dispersion, and impact. We focus here on the reproducible aerosolization and injection of viable microorganisms into an ASC, the first and crucial step of any experimental protocol to expose bio-aerosols to different atmospheric conditions. We compare the performance of three nebulizers specifically designed for bio-aerosol applications: the Collison nebulizer, the Blaustein Atomizing Modules (BLAM), and the Sparging Liquid Aerosol Generator (SLAG), all manufactured and commercialized by CH TECHNOLOGIES. The comparison refers to operating conditions and the concentration of viable bacteria at the nebulizer outlet, with the final goal being to measure the reproducibility of the nebulization procedures and assess their application in experiments inside ASCs. A typical bacterial test model, Escherichia coli (ATCC\uae 25922\u2122), was selected for such characterization. Bacteria suspensions with a concentration around 108 CFUmL1 were first aerosolized at different air pressures and collected by a liquid impinger to obtain a correlation curve between airflow and nebulized bacteria for each generator. Afterwards, bacteria were aerosolized inside the atmospheric simulation chamber ChAMBRe (Chamber for Aerosol Modelling and Bio-aerosol Research) to measure the reproducibility of the whole procedure. An overall reproducibility of 11% (i.e., standard deviation of the results obtained with the three nebulizers) was obtained with each nebulizer through a set of baseline experiments

Towards a UK Airborne Bioaerosol Climatology: Real-Time Monitoring Strategies for High Time Resolution Bioaerosol Classification and Quantification

Biological particulate matter (BioPM) is a poorly constrained, ubiquitous, and diverse subset of atmospheric aerosols. They influence climate, air quality, and health via many mechanisms, spurring renewed interest in constraining their emissions to elucidate their impacts. In order to build the framework required to assess the role of BioPM in these multidisciplinary areas, it is necessary to develop robust, high time-resolution detection methodologies so that BioPM emissions can be understood and characterized. In this study, we present ambient results from intensive monitoring at UK peri-urban and coastal ground sites using high time-resolution real-time bioaerosol spectrometers. We demonstrate the utility of a new dimensional reduction-driven BioPM classification scheme, where laboratory sample training data collected at the ChAMBRe facility were used to generate broad taxonomic class time series data of key species of interest. We show the general trends of these representative classes, spanning spring, early summer, and autumn periods between 2019 and 2021. Diurnal behaviors and meteorological relationships were investigated and contextualized; a key result arising from this study was the demonstration of rainfall-induced enhancement of nighttime Penicillium-like aerosol, where rainfall crucially only acts to enhance the quantity emitted without significantly influencing the early morning timing of peak spore liberation

Studio multispettrale del fattore correttivo Cref determinato dal confronto tra osservazioni di MAAP, MWAA, AE31, AE33, influenza di SSA e stato di aging

International audienceLa frazione assorbente dell’aerosol atmosferico ha un impatto rilevante sul bilancio radiativo terrestre agendo come forzante climatica positiva. Accurate misure in situ multispettrali del coefficiente di assorbimento e del MACBC (black carbon mass absorption cross section, m2/g), oltre allo studio della sua variabilità in atmosfera, sono cruciali per una migliore stima del suo impatto. L’aethalometro è ad oggi lo strumento più diffuso per la misura del coefficiente di assorbimento a più lunghezze d’onda (370-950 nm). Il principio di funzionamento si basa sulla misura della luce trasmessa da un campione di aerosol depositato su filtro ed è sensibile al livello di accumulo delle particelle (loading effect), che causa una sottostima del coefficiente di assorbimento, e soggetto a sovrastime dovute allo scattering multiplo prodotto dal filtro e dalle particelle non assorbenti. Mentre il primo artefatto può essere corretto sia a posteriori tramite algoritmi sia in automatico [1,2], l’effetto di scattering multiplo necessita invece di un parametro correttivo denominato Cref. Questo è tipicamente ricavato per confronto con tecniche indipendenti come il MAAP (online, 637 nm) e l’MWAA (off-line, 4 lunghezze d’onda), in cui il coefficiente di assorbimento è ricavato tramite un modello di trasferimento radiativo applicato alla luce riflessa e trasmessa dal campione a diversi angoli [3]. La stima del parametro Cref e lo studio della sua variabilità in ambiente e in condizioni controllate è di grande importanza per migliorare l’accuratezza delle osservazioni “filter-based.In questo studio si presentano i risultati del confronto tra diverse tecniche “filter-based” per la misura del coefficiente di assorbimento e la stima del fattore correttivo Cref sulla base di misure di terreno realizzate in ambienti caratterizzati da aerosol di tipo e proprietà diverse (Monte Cimone, San Pietro Capofiume e Bologna, luglio 2017) e da esperimenti effettuati nella camera di simulazione CESAM (https://cesam.cnrs.fr/) su BC fresco generato tramite miniCAST JING e invecchiato in presenza di coating organico (H2O+O3+α-pinene) e inorganico (H2O+O3+SO2+luce). I valori ricavati compresi tra 2 e 6 si mostrano in accordo con altri risultati in letteratura. L’integrazione dei dati di terreno e di camera ha permesso la determinazione e lo studio del Cref per AE31 e AE33 e la sua dipendenza da differenti parameteri quali la SSA (frazione di assorbimento), l’umidità relativa, la concentrazione di BC, e lo stato di mixing dell’aerosol