New diffused aeration photocatalytic reactor (DAPR) for organics removal from oil-in-water samples: study of the beneficial effect of air-stripping

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Hydrocarbon removal from bilgewater by a combination of air-stripping and photocatalysis

AIR:EAU+DCA:LFI:CFE:JMCIn order to prevent hydrocarbon discharge at sea from the bilge of ships, the International Maritime Organization (IMO) enacted the MARPOL 73/78 convention in which effluents are now limited to those with maximum oil content of 15 ppmv. Thus, photocatalysis and air-stripping were combined for the hydrocarbon removal from a real oily bilgewater sample and an original monitoring of both aqueous and gaseous phases was performed by GC/MS to better understand the process. Our results show that the hydrocarbon oil index [HC] can be reduced to its maximum permissible value of 15 ppmv (MARPOL) in only 8.5 h when photocatalysis and air-stripping are used together in a synergistic way, as against 17h when photocatalysis is used alone. However, this air-assisted photocatalytic process emits a large quantity of volatile organic compounds (VOC) and, within the first four hours, ca. 10% of the hydrocarbon removal in the aqueous phase is actually just transferred into the gaseous one. Finally, we highlight that the n-alkanes with a number of carbon atoms higher than 15 (N-C > 15) are those which most decrease the rate of [HC] removal

Optical and chemical properties of aged biomass burning aerosols

SSCI-VIDE+CARE+DCA:CGOInternational audienceAmong the organic compounds emitted during biomass burning events, methoxyphenols (45%wt. of the particulate matter derived from wood smoke) are present both in the gas and particle phases, and may undergo various transformations during atmospheric ageing induced either by light (photochemistry) or temperature (thermal processes).We report here chemical and optical analyses of syringol (C8H10O3) particles, one of the most abundant methoxyphenol species found in such biomass burning plumes, after both photo- and thermal-ageing. Chemical analyses were performed using a HESI/LC/DAD/MS (orbitrap mass spectrometry). When exposed to UV-light or heated for several hours, syringol became yellowish in both cases while distinct products were identified. The differences in chemistry propagate also to the optical properties of the aerosols as probed by broad band cavity enhanced spectroscopy (BBCES). These results, when considered together, may be of importance considering the possible effects on human health of these detected ageing-products and the contribution to the radiative forcing.This work is supported by the Ministère des Affaires Etrangères et du Développement International (France) and the Ministry of Science (Israel), under the Research Program "Maïmonide-Israel". Two groups collaborate for it: Christian George group (CNRS, FRANCE) for the high resolution MS chemical analyses and Yinon Rudich group (Weizmann Institute, ISRAEL) for the optical properties of aerosols

Heterogeneous photochemistry of gaseous NO2 on solid fluoranthene films: A source of gaseous nitrous acid (HONO) in the urban environment

AIR+DCA:MBG:ARA:CGOInternational audienceUsing a coated flow tube equipped with several near-ultraviolet emitting lamps, (range 300-420 nm), we examined the effect of actinic radiation on the heterogeneous loss kinetics of gaseous nitrogen dioxide on solid Polycyclic Aromatic Hydrocarbon (PAH) films deposited on a Pyrex substrate. The PAH studied was mainly fluoranthene, with additional tests on phenanthrene and pyrene. No dependence of the uptake coefficient (gamma) was observed either with temperature, or with relative humidity. In the dark, the reaction was very slow but was greatly enhanced by increasing the UV-A light intensity. A linear dependency of the reaction kinetics with the photonic flux was observed. Under atmospherically-relevant NO2 concentrations (20 ppbv), the uptake coefficient was about 1 x 10(-6). The uptake coefficient variation as a function of the NO2 concentration suggests a Langmuir-Hinshelwood (L-H) type mechanism. This is characterized by the adsorption of NO2 on the solid surface followed by a chemical reaction. The corresponding equilibrium constant (K') and the surface reaction rate constant (k(s)(1)) were found to be 3 x 10(-2) ppbv(-1) and 5 x 10(-5) s(-1) respectively for the photo-enhanced uptake of NO2 on the fluoranthene substrate. Particular attention was given to the detection of the gas-phase products showing the photo-enhanced reduction of NO2 to HONO and NO via a photosensitized reaction involving excited states of the PAH. Additionally we investigated the reactivity of PAH in the presence of nitrates in order to better understand if HONO generation mechanism could be explained by a first deposition of nitrates (generated via NO2 hydrolysis) on the solid surface. (C) 2013 Elsevier B.V. All rights reserved

Analysis of gas phase intermediates and mineralization during the photocatalytic oxidation of organic pollutants: a critical step towards the performance evaluation

AIR:EAU+DCA:DVI:MSL:CFE:LFI:JMCThis work illustrates the capabilities of two advanced analytical methods, Automated Thermal Desorption/Gas Chromatography/Mass Spectrometry, (ATD/GC/MS) and Gas Chromatography, Pulse Discharge Helium Ionization Detector, (GC/PDHID) for a better understanding of the photocatalytic degradation of organic compounds in air at ppb(v) levels. For this purpose two compounds, viz. dichlorvos and 2-propanol were chosen and the influence of relative humidity (RH%) on the oxidation efficiency was investigated. According to the RH levels, different mechanisms of degradation as well as rate of mineralization were proposed. For example at 40% RH, the main reaction intermediates coming from dichlorvos degradation was dichloroacetaldehyde while traces of phosgene were observed. In contrast, at 0% RH, trichloroacetaldehyde was found to be the main intermediate and a higher amount of phosgene was observed. When only the conversion rate was followed, it was impossible to assess the photocatalytic efficiency of the air cleaning system since whatever RH values considered, high rates of conversion were always measured. However using PDHID detector it was possible to calculate the rate of mineralization which varies drastically as a function of RH: a decrease in the mineralization rate with increasing RH is shown. In addition, it was shown that during photocatalytic treatment of bilge water in an aerated reactor, volatile organic compounds (VOCs) were emitted which are potential source of pollution for workers in engine room. In this case, an additional treatment of the gaseous phase would be necessary

Impact of reactive uptake of oxygenated volatile organic compounds on acidic aerosols on SOA formation

SSCI-VIDE+CARE+CUB:RGM:DCA:SPR:CGO:MRVInternational audienceThe importance of the secondary organic aerosol (AOS) in the atmosphere motivate the scientific community to study their formation mechanisms. Despite the important number of studies on the formation and aging of SOA, this field remains poorly characterized.The volatile organic compounds (VOC) can be oxygenated to form the oxygenated volatile organic compounds (OVOCs) with different volatility related to a different oxygenation degree. The OVOCs with low volatility have a facility to condense on the aerosols and to form AOS. In 2006 Liggio et al had shown that the OVOCs can contribute to the AOS formation by reactive uptake. This way of AOS formation is still little studied. In our study we are interested to understand this mechanism and to study its influence and contribution on the AOS formation.The experimental concept consist to generate acid aerosol with a TSI atomizer (model 3706). A diffusion dryer (model 3062, TSI,US) was used to decrease the aerosol humidity. A differential mobility analyzer (DMA 3081, TSI, US, impactor size 0.071 cm), was placed downstream of the particle generation assembly and was set to select particles in the required size range (100 nm) The particle stream leaving the DMA was diluted with pure air to obtain a total mass of few μg m-3. It was flown into a flow tube (18 L) where it was exposed to gaseous OVOC. We tested two residence times in the flow tube (15 and 30 minutes). At the exist of the flow tube the aerosol size distribution are measured by a Scanning Mobility Particle Sizer (SMPS) and the aerosol chemical composition are measured by an aerosol mass spectrometer (C-ToF-AMS).A reaction between an acid aerosol and an epoxide (α-pinene oxide) was used to validate the experimental setup. We compare our results to the results obtained by Xu, Wen et al for the same chemical reaction. To follow the epoxide reactive uptake on the ammonium bisulfate we based us on the Sulfate/organic ratio evolution.Liggio, John, and Shao‐Meng Li. "Reactive uptake of pinonaldehyde on acidic aerosols." Journal of Geophysical Research: Atmospheres 111.D24 (2006).Xu, Wen, et al. "Acid-catalyzed reactions of epoxides for atmospheric nanoparticle growth." Journal of the American Chemical Society 136.44 (2014): 15477-15480

Impact of reactive uptake of oxygenated volatile organic compounds on acidic aerosols on SOA formation

SSCI-VIDE+CARE+CUB:RGM:DCA:SPR:CGO:MRVInternational audienceThe importance of the secondary organic aerosol (AOS) in the atmosphere motivate the scientific community to study their formation mechanisms. Despite the important number of studies on the formation and aging of SOA, this field remains poorly characterized.The volatile organic compounds (VOC) can be oxygenated to form the oxygenated volatile organic compounds (OVOCs) with different volatility related to a different oxygenation degree. The OVOCs with low volatility have a facility to condense on the aerosols and to form AOS. In 2006 Liggio et al had shown that the OVOCs can contribute to the AOS formation by reactive uptake. This way of AOS formation is still little studied. In our study we are interested to understand this mechanism and to study its influence and contribution on the AOS formation.The experimental concept consist to generate acid aerosol with a TSI atomizer (model 3706). A diffusion dryer (model 3062, TSI,US) was used to decrease the aerosol humidity. A differential mobility analyzer (DMA 3081, TSI, US, impactor size 0.071 cm), was placed downstream of the particle generation assembly and was set to select particles in the required size range (100 nm) The particle stream leaving the DMA was diluted with pure air to obtain a total mass of few μg m-3. It was flown into a flow tube (18 L) where it was exposed to gaseous OVOC. We tested two residence times in the flow tube (15 and 30 minutes). At the exist of the flow tube the aerosol size distribution are measured by a Scanning Mobility Particle Sizer (SMPS) and the aerosol chemical composition are measured by an aerosol mass spectrometer (C-ToF-AMS).A reaction between an acid aerosol and an epoxide (α-pinene oxide) was used to validate the experimental setup. We compare our results to the results obtained by Xu, Wen et al for the same chemical reaction. To follow the epoxide reactive uptake on the ammonium bisulfate we based us on the Sulfate/organic ratio evolution.Liggio, John, and Shao‐Meng Li. "Reactive uptake of pinonaldehyde on acidic aerosols." Journal of Geophysical Research: Atmospheres 111.D24 (2006).Xu, Wen, et al. "Acid-catalyzed reactions of epoxides for atmospheric nanoparticle growth." Journal of the American Chemical Society 136.44 (2014): 15477-15480

Heterogeneous Photochemistry in the Atmosphere

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