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Biomass burning emissions in Amazonia change the atmospheric composition and aerosol properties during the dry season. We investigated fine-mode aerosol chemical composition and optical properties with an intensive field experiment in the dry-to-wet season transition in 2018 in Southwestern Amazonia. Aerosol composition and physical properties were measured using ACSMs, aethalometers, nephelometers, SMPSs, and CPCs. PM1 mass concentrations showed a mean value of 12.4 ± 10.1 μg m−3. Organic matter was the major constituent of PM1, contributing more than 75%, whereas black carbon (BC) contributed ∼15%, and inorganics were less than 10%. The organic fraction of PM1 was apportioned by positive-matrix factorization (PMF), resolving 4 organic aerosol (OA) factors: two oxygenated OAs (OOA-1 and OOA-2), one hydrocarbon-like (HOA), and one biomass burning OA (BBOA). A low single scattering albedo (637 nm) of 0.77 ± 0.08 was observed, suggesting a significant absorption material. BC and brown carbon (BrC) contributions to the absorption coefficient (470 nm) were retrieved, and BrC corresponded, on average, to 20% of total absorption. The mass scattering (MSE) and absorption efficiencies (MAE) of PM1 particles were determined by multilinear regression (MLR), using the PMF factors as predictor variables. Overall, organic aerosols showed significant light absorption in the UV-vis wavelength range and strong spectral dependence indicating the presence of organic species that act as BrC, predominantly associated with biomass burning OAs. Our results emphasize the need for a better understanding of links between aerosol composition and optical properties, including the absorption spectra of BrC in the Amazon.

SSCI-VIDE+CARE+LBT:FDA:MPO:CGO:CGU; International audience; Transforming pollution into valuable compounds and more especially into energy is an important challenge for a sustainable future. The objective of our work was to better understand the mechanism of the photocatalytic degradation of acetic acid (AA) in the gas phase under an air or oxygen-free atmosphere, by comparing the disappearance, mineralization and selectivity of the intermediate products formed in the presence of non-doped TiO2. It was found that in both environments decarboxylation is the first step of AA degradation. However, the fate of the methyl group depends on the carrier gas and gas phase concentration. In air, at low AA molar flow the methyl group is oxidized into methanol, formaldehyde, and CO2 with no formic acid detected. At molar flows larger than 0.55 p,moli min, corresponding to the saturation of the TiO2 surface, ethane is formed due tothe combination of two methyl groups. In an O-2-free atmosphere, three new products were detected: methane (CH4), acetone (CH3COCH3) and acetaldehyde (CH3COH). However, the use of (CH3COOH)-C-13 shows that acetone and acetaldehyde do not arise from the reduction of the carboxylic group. Under air, a mechanism explaining the formation of methanol, formaldehyde and ethane occurring on the surface of TiO2, involving either a direct oxidation of AA with the holes or an oxidation with the hydroxyl radicals was proposed, together with the regeneration of the TiO2 surface and the formation of H2O2. (C) 2017 Elsevier B.V. All rights reserved.

SSCI-VIDE+CARE+CEM:CGO; International audience; Dicarboxylic acids have low volatilities and hence are present mostly in the particulate phase, including the surface of dust particles. Mineral dust, globally the mostemitted aerosol, has photocatalytic properties that can initiate photo-induced heterogeneous chemistry of organic compounds, which is still poorly characterized. Weinvestigated the photochemistry offive dicarboxylic acids (DCA) i.e., succinic (butanedioic) acid, glutaric (pentanedioic) acid, adipic (hexanedioic) acid, pimelic(heptanedioic) acid and suberic (octanedioic) acid on Arizona test dust (ATD) particles upon UV-A light irradiation (0–1.4 mW cm−2). Gas-phase products weremonitored by a high-resolution proton-transfer-reaction mass spectrometer (PTR-ToF-MS), and surface sorbed products were extracted and analyzed by ultra-high-performance liquid chromatography coupled to a heated electrospray ionization high-resolution mass spectrometer (UHPLC-HESI-HRMS). Monoacids and aldehydeswere the main observed and quantified gaseous products. In contrast, shorter chain DCA and highly oxygenated products were found at the surface of the dustparticles. Interestingly, the photochemistry of these DCAs presented an even-odd alternation concerning their heterogeneous reactivity, with odd-numbered carbondiacids being more reactive than their even-numbered homologous ones. We present and discuss a reaction mechanism for the C4–C8DCA heterogeneous photo-oxidation catalysed by TiO2/Fe2O3-rich dust particles. Our results suggest that photochemical processing on dust surfaces should be regarded as a possible efficient pathway for altering their surface properties impacting ice nucleation and cloud condensation properties

Heterogeneous photocatalytic oxidation systems using titanium dioxide (TiO2) have been extensively studied for the removal of several volatile organic compounds (VOCs). The addition of noble metals such as palladium on TiO2 may improve photocatalytic activity by increasing charge separation efficiency. In this work, palladium was impregnated on TiO2 and the efficiency of the new catalyst was tested and compared with that of pure TiO2. Pd was impregnated on TiO2 by the reduction method, using NaBH4, and was characterized by XRD, XPS, UV–Vis, and H2 chemisorption. The photocatalytic tests were performed in an annular coated-wall reactor using octane, isooctane, n-hexane, and cyclohexane at inlet concentrations varying from 100 to 120 ppmv. Compared with pure TiO2 film, the photocatalytic activity of TiO2 impregnated with 1 wt% of palladium was improved. All the aforementioned analytical techniques confirmed the presence of Pd incorporated into the structure of TiO2, and the conversion rates were studied in a broad range of residence times, yielding up to 90 % or higher rates in 40 s of residence time, thus underscoring the relevant contribution of the technology Fechado

SSCI-VIDE+CARE+MPO:CGO; International audience; 10 Mineral dust particles have photochemical properties that can promote heterogeneous reactions on 11 their surfaces and therefore alter atmospheric composition. Even though dust photocatalytic nature 12 has received significant attention recently, most studies have focused on inorganic trace gases. Here 13 we investigated how light changes the chemical interactions between butanol and Arizona test dust, 14 a proxy for mineral dust, under atmospheric conditions. Butanol uptake kinetics were measured, 15 exploring the effects of UV light irradiation intensity (0-1.4 mW/cm), relative humidity (0-10%), 16 temperature (283-298 K), and butanol initial concentration (20-55 ppb). The composition of the 17 gas phase was monitored by a high-resolution proton-transfer-reaction mass spectrometer (PTR-ToF-18 MS) operating in H3O + mode. Water was observed to play a significant role, initially reducing 19 heterogeneous processing of butanol, but enhancing reaction rates once it evaporated. Gas phase 20 products were identified, showing that surface reactions of adsorbed butanol led to the emission of a 21 variety of carbonyl containing compounds. Under actinic light these compounds will photolyze and 22 produce hydroxyl radicals, changing dust processing from a sink of VOC into a source of reactive 23 compounds. 24 25