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Carbonaceous soot particles are formed during incomplete combustion of fossil fuels, biofuels or biomass and are considered to be a significant proportion of aerosol emission, especially in polluted areas, and to contain light-absorbing carbon fractions. The light-absorbing carbon components make these particles exhibit positive radiative forcing and thus they contribute to atmospheric warming processes. The exact contribution to this process however still has significant uncertainties. One of the sources of uncertainty is related to the capacity to accurately describe soot spectral optical properties (MAC/MSC/MEC - mass absorption/scattering/extinction cross-sections in m2g-1; CRI - complex refractive index), due to significant uncertainties for key measurements like the absorption coefficient or absorbing mass fraction. A second source is considered to be the change of the optical properties with the variable physico-chemical state of soot (e.g. chemical composition, morphology, primary particle size, aggregate size distribution, coating and mixing state) which depends on (i) the combustion conditions/sources and is (ii) known to change during atmospheric lifetime due to ageing and mixing processes.The present work aims at providing new measurements of soot spectral optical properties and investigating their dependence on particles’ physico-chemical state and the role of measurement uncertainties. For this, a set of original experiments was performed in the 4.3m3 CESAM atmospheric simulation chamber (https://cesam.cnrs.fr/) on soot aerosols generated by a commercial propane diffusion flame soot generator (miniCAST model 6204 TYPE C, JING). In these experiments, the variability of soot properties due to (i) generation and (ii) atmospheric ageing was explored. Different combustion conditions going from fuel–leaner to fuel-richer were set to produce soot aerosol with different effective densities, EC/TC-ratios ranging from 0.8 ± 0.1 to 0.0 ± 0.1 and size distributions with median diameters between 30 and 120 nm. Selected aerosols were subjected to ageing in a N2/O2 atmosphere under simulated atmospheric conditions (humid, with/without illumination, up to 26 hours lifetime). In these conditions, physical and chemical ageing, under the presence of different gaseous phases (O3, SO2) and addition of a second aerosol phase produced by photo-oxidation of SO2 or the ozonolysis of α-pinene, led to changes in the physico-chemical properties of the soot.State-of-the-art techniques were used to generate an extensive dataset of physico-chemical parameters (mass concentration, morphology, effective density, composition, size distribution) and spectral optical properties (absorption, scattering, extinction coefficients) for different soot aerosols and different ageing states of these. The absorption coefficient in particular was measured by both filter-based (AE - Aethalometer, MAAP - Multi-Angle Absorption Photometer, MWAA – Multi-Wavelength Absorbance Analyzer, PP_UniMI - Polar Photometer by University of Milano) and extinction minus scattering techniques. The MAC, MSC and MEC datasets, retrieved by combining these measurements, will be presented for the ensemble of chamber experiments and the variability of these parameters in link with variations in the particles’ physico-chemical properties will be discussed together with key relevant uncertainties.

Bio-aerosols consist of airborne particles such as pollens, fungi, bacteria, viruses and debris from biological matter, such as metabolites and toxins, that are present ubiquitously in the environment. In last decades, the interest in bioaerosols has increased rapidly to broaden the pool of knowledge on their identification, quantification, distribution, but also to understand how bioaerosols impact human health in both indoor and outdoor settings. Experiments conducted inside confined artificial environments, such as the Atmospheric Simulations Chambers (ASCs), where atmospheric conditions and composition are controlled, can provide valuable information on bio-aerosol viability, dispersion, and impact. At ChAMBRe (Chamber for Aerosol Modelling and Bio-aerosol Research), a 2.3 m3 stainless steel ASC, managed by INFN at the Physics Department of the University of Genoa, Italy, the research on bioaerosol is focused on the investigation of the airborne bacteria behavior in different atmospheric conditions (Massabò et al., AMT, 2018). Our experiments were performed with two types of bacteria, Bacillus Subtilis and Escherichia Coli evolutionarily divergent model organisms, Gram-negative and Gram-positive respectively, to compare cellular viability by varying of the atmospheric conditions in the simulation chambre. A great effort has been put in the assessment of an experimental protocol which includes bacteria cultivation, injection in the chamber of viable cells, exposure to peculiar environmental conditions and final verification of the loss/gain in viability. With first experiments, bacteria were exposed to high concentration of characterized soot particles (Black carbon ~ 600 μg m-3) and NOx exhausts, both produced by propane combustion (Vernocchi et al., 2021). The effects of NOx only were also separately investigated, in another set of experiments, in which different concentration of NOx were tested. Evidence of an impact of NOx concentration on the viability of the Gram-negative Bacillus Subtilis were observed and will be fully reported at the conference.

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–optical 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 Ångström 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.

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. 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-optical techniques, to measure the spectral dependence of the absorption coefficient b_abs, and their composition in terms of Elemental and Organic Carbon (EC and OC). Significant differences could be observed when the MISG is fuelled with ethylene and propane both in terms of particle size and optical behaviour (i.e., absorption coefficient). Values of the Mass Absorption Coefficient (MAC) and of the Angstrom Absorption Exponent (AAE) turned out to be compatible with the literature, even if with some specific difference. The comprehensive characterization of the MISG soot particles is an important piece of information to design and perform experiments in atmospheric simulation chambers.

Thermal–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 from several uncertainties and artifacts such 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 behavior 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 thermal–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 instrument, the unit has been modified at the physics department of the University of Genoa (Italy), making possible the alternative use of the standard laser diode at λ=635 nm and of a new laser diode at λ=405 nm. In this way, the optical transmittance through the sample can be monitored at both wavelengths. Since at shorter wavelengths the BrC absorbance is higher, a better sensitivity to this species is gained. The modified instrument also gives the possibility to quantify the BrC concentration in the sample at both wavelengths. The new unit has been thoroughly tested, with both artificial and real-world aerosol samples: the first experiment, in conjunction with the multi-wavelength absorbance analyzer (MWAA; Massabò et al., 2013, 2015), resulted in the first direct determination of the BrC mass absorption coefficient (MAC) at λ=405 nm: MAC =23±1 m2 g−1.

The interplay of bio-aerosol dispersion and impact, meteorology, air quality is gaining increasing interest in the wide spectrum of atmospheric science. Experiments conducted inside confined artificial environments, such as the Atmospheric Simulations 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-aerosol at different atmospheric conditions. We compare the performance of three nebulizers specifically designed for bioaerosol 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 to measure the reproducibility of the nebulization procedure and assess the application in experiments at ASCs. A typical bacterial test model, Escherichia coli (ATCC® 25922™), was selected for such characterization. Bacteria suspensions, with a concentration around 108 CFU ml−1, 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 % was obtained with each nebulizer through a set of baseline experiments.