The relative importance of competing pathways for the formation of high-molecular-weight peroxides in the ozonolysis of organic aerosol particles

High-molecular-weight (HMW) organic compounds are an important component of atmospheric particles, although their origins, possibly including in situ formation pathways, remain incompletely understood. This study investigates the formation of HMW organic peroxides through reactions involving stabilized Criegee intermediates (SCI's). The model system is methyl oleate (MO) mixed with dioctyl adipate (DOA) and myristic acid (MA) in submicron aerosol particles, and Criegee intermediates are formed by the ozonolysis of the double bond in methyl oleate. An aerosol flow tube coupled to a quadrupole aerosol mass spectrometer (AMS) is employed to determine the relative importance of different HMW organic peroxides following the ozonolysis of different mixing mole fractions of MO in DOA and MA. Possible peroxide products include secondary ozonides (SOZ's), α-acyloxyalkyl hydroperoxides and α-acyloxyalkyl alkyl peroxides (αAAHP-type compounds), diperoxides, and monoperoxide oligomers. Of these, the AMS data identify two SOZ's as major HMW products in the ozonolysis of pure methyl oleate as well as in an inert matrix of DOA to as low as 0.04 mole fraction MO. In comparison, in mixed particles of MO and MA, αAAHP-type compounds form in high yields for MO mole fractions of 0.5 or less, suggesting that SCI's efficiently attack the carboxylic acid group of myristic acid. The reactions of SCI's with carboxylic acid groups to form αAAHP-type compounds therefore compete with those of SCI's with aldehydes to form SOZ's, provided that both types of functionalities are present at significant concentrations. The results therefore suggest that SCI's in atmospheric particles contribute to the transformation of carboxylic acids and other protic groups into HMW organic peroxides

Design of a new multi-phase experimental simulation chamber for atmospheric photosmog, aerosol and cloud chemistry research

A new simulation chamber has been built at the Interuniversitary Laboratory of Atmospheric Systems (LISA). The CESAM chamber (French acronym for Experimental Multiphasic Atmospheric Simulation Chamber) is designed to allow research in multiphase atmospheric (photo-) chemistry which involves both gas phase and condensed phase processes including aerosol and cloud chemistry. CESAM has the potential to carry out variable temperature and pressure experiments under a very realistic artificial solar irradiation. It consists of a 4.2 m<sup>3</sup> stainless steel vessel equipped with three high pressure xenon arc lamps which provides a controlled and steady environment. Initial characterization results, all carried out at 290–297 K under dry conditions, concerning lighting homogeneity, mixing efficiency, ozone lifetime, radical sources, NO<sub>y</sub> wall reactivity, particle loss rates, background PM, aerosol formation and cloud generation are given. Photolysis frequencies of NO<sub>2</sub> and O<sub>3</sub> related to chamber radiation system were found equal to (4.2 × 10<sup>−3</sup> s<sup>−1</sup>) for <i>J</i><sub>NO<sub>2</sub></sub> and (1.4 × 10<sup>−5</sup> s<sup>−1</sup>) for <i>J</i><sub>O<sup>1</sup>D</sub> which is comparable to the solar radiation in the boundary layer. An auxiliary mechanism describing NO<sub>y</sub> wall reactions has been developed. Its inclusion in the Master Chemical Mechanism allowed us to adequately model the results of experiments on the photo-oxidation of propene-NO<sub>x</sub>-Air mixtures. Aerosol yields for the α-pinene + O<sub>3</sub> system chosen as a reference were determined and found in good agreement with previous studies. Particle lifetime in the chamber ranges from 10 h to 4 days depending on particle size distribution which indicates that the chamber can provide high quality data on aerosol aging processes and their effects. Being evacuable, it is possible to generate in this new chamber clouds by fast expansion or saturation with or without the presence of pre-existing particles, which will provide a multiphase environment for aerosol-droplet interaction

Density changes of aerosol particles as a result of chemical reaction

International audienceThis paper introduces the capability to study simultaneously changes in the density, the chemical composition, the mobility diameter, the aerodynamic diameter, and the layer thickness of multi-layered aerosol particles as they are being altered by heterogeneous chemical reactions. A vaporization-condensation method is used to generate aerosol particles composed of oleic acid outer layers of 2 to 30 nm on 101-nm polystyrene latex cores. The layer density is modified by reaction of oleic acid with ozone for variable exposure times. For increasing ozone exposure, the mobility diameter decreases while the vacuum aerodynamic diameter increases, which, for spherical particles, implies that particle density increases. The aerosol particles are confirmed as spherical based upon the small divergence of the particle beam in the aerosol mass spectrometer. The particle and layer densities are calculated by two independent methods, namely one based on the measured aerodynamic and mobility diameters and the other based on the measured mobility diameter and particle mass. The uncertainty estimates for density calculated by the second method are two to three times greater than those of the first method. Both methods indicate that the layer density increases from 0.89 to 1.12 g·cm?3 with increasing ozone exposure. Aerosol mass spectrometry shows that, concomitant with the increase in the layer density, the oxygen content of the reacted layer increases. Even after all of the oleic acid has reacted, the layer density and the oxygen content continue to increase slowly with prolonged ozone exposure, a finding which indicates continued chemical reactions of the organic products either with ozone or with themselves. The results of this paper provide new insights into the complex changes occurring for atmospheric particles during the aging processes caused by gas-phase oxidants

Electromagnetic heating for industrial kilning of malt: a feasibility study

Industrial malting operations use ~800kWh/t of energy to produce the heat required to kiln malt. Electromagnetic heating technologies are suggested as a way to potentially improve the energy efficiency of the kilning processing. In this work, the potential for using electromagnetic heating to dry malt to commercially acceptable moisture levels, whilst preserving the activity of enzymes critical for downstream brewing processes is investigated. The 2450 MHz bulk dielectric properties of malt at moisture contents consistent with those occurring at different points in the kilning process are evaluated; 12% is shown to be a critical moisture level below which drying becomes more energy intensive. Calculated penetration depths of electromagnetic energy in malt at radio frequency are 100 fold higher than at microwave frequencies, showing a significant advantage for commercial scale batch processing. The moisture contents and alpha and beta amylase activity of malt subjected to RF heating at different temperatures, treatment times and RF energy inputs in the intermediate and bound water drying regions were determined. It is shown for the first time that whilst significantly reduced process times are attainable, significant energy efficiency improvements compared to conventional kilning can only be achieved at higher product temperatures and thus at the expense of enzyme survival. It is suggested that RF heating may be feasible where higher bulk temperatures are not critical for downstream use of the material or when used in hybrid systems

Towards large scale microwave treatment of ores: Part 2 - Metallurgical testing

A pilot scale microwave treatment system capable of treating 10-150t/h of material at 10-200kW was designed, constructed and commissioned in order to understand the engineering challenges of microwave-induced fracture of ores at scale and generate large metallurgical test samples of material treated at approximately 0.3-3kWh/t. It was demonstrated that exposing more of the ore to a region of high power density by improving treatment homogeneity with two single mode applicators in series yielded equivalent or better metallurgical performance with up to half the power and one third the energy requirement of that used with a single applicator. Comminution testing indicated that A*b values may be reduced by up to 7-14% and that the Bond Ball Mill Work Index may be reduced by up to 3-9% depending on the ore type under investigation. Liberation analysis of the microwave-treated ore indicated that equivalent liberation may be achievable for a grind size approximately 40-70µm coarser than untreated ore, which is in agreement with laboratory scale investigations reported in the literature at similar or higher doses. Flow sheet simulations further indicated that reduced ore competency following microwave treatment could potentially yield up to a 9% reduction in specific comminution energy (ECS) at a nominal plant grind of P₈₀190µm, or up to 24% reduction at a grind of P₈₀290µm, for a microwave energy input of 0.7-1.3kWh/t. Throughput could also be increased by up to approximately 30% depending on grind size, ore type and equipment constraints. To date, approximately 900t of material has been processed through the pilot plant, approximately 300t of which was under microwave power. Metallurgical testing has demonstrated that comminution and liberation benefits are achievable at doses lower than that previously reported in the literature, which allow high throughputs to be sustained with low installed power requirements providing a pathway to further scale-up of microwave treatment of ores

Design and Optimisation of a Microwave Reactor for Kilo-Scale Polymer Synthesis

Current industrial production of polymer resins is generally undertaken in large multi-tonne stirred tank reactors. These are characterised by relatively slow heating and cooling cycles, resulting in long vessel cycle times and extended production campaigns. In this work we present a design for a hybrid microwave/oil jacket proof of concept system capable of producing up to 4.1 kg of polymer resin per batch. By exploiting rapid volumetric heating effects of microwave energy at 2.45GHz, we have optimised the synthetic regime, such that a 3.7 kg batch of polyester resin pre-polymer can be made in only 8 hours 20 minutes, with higher molecular weight (Mn 2,100) compared to the conventional process taking 22 hours 15 minutes (Mn 1,200), yielding an increase in synthesis rate of at least 265. The increase in polymer molecular weight also suggests a higher conversion was achieved over a shorter time scale

Design and optimisation of a microwave reactor for kilo-scale polymer synthesis

Current industrial production of polymer resins is generally undertaken in large multi-tonne stirred tank reactors. These are characterised by relatively slow heating and cooling cycles, resulting in long vessel cycle times and extended production campaigns. In this work we present a design for a hybrid microwave/oil jacket proof of concept system capable of producing up to 4.1?kg of polymer resin per batch. By exploiting rapid volumetric heating effects of microwave energy at 2.45?GHz, we have optimised the synthetic regime, such that a 3.7?kg batch of polyester resin pre-polymer can be made in only 8?h 20?min, with higher molecular weight (Mn 2100) compared to the conventional process taking 22?h 15?min (Mn 1200), yielding an increase in synthesis rate of at least 265%. The increase in polymer molecular weight also suggests a higher conversion was achieved over a shorter time scale

Pseudomonas aeruginosa is capable of natural transformation in biofilms

Natural transformation is a mechanism that enables competent bacteria to acquire naked, exogenous DNA from the environment. It is a key process that facilitates the dissemination of antibiotic resistance and virulence determinants throughout bacterial populations. Pseudomonas aeruginosa is an opportunistic Gram-negative pathogen that produces large quantities of extracellular DNA (eDNA) that is required for biofilm formation. P. aeruginosa has a remarkable level of genome plasticity and diversity that suggests a high degree of horizontal gene transfer and recombination but is thought to be incapable of natural transformation. Here we show that P. aeruginosa possesses homologues of all proteins known to be involved in natural transformation in other bacterial species. We found that P. aeruginosa in biofilms is competent for natural transformation of both genomic and plasmid DNA. Furthermore, we demonstrate that type-IV pili (T4P) facilitate but are not absolutely essential for natural transformation in P. aeruginosa

A global genomic approach uncovers novel components for twitching motility-mediated biofilm expansion in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is an extremely successful pathogen able to cause both acute and chronic infections in a range of hosts, utilizing a diverse arsenal of cell-associated and secreted virulence factors. A major cell-associated virulence factor, the Type IV pilus (T4P), is required for epithelial cell adherence and mediates a form of surface translocation termed twitching motility, which is necessary to establish a mature biofilm and actively expand these biofilms. P. aeruginosa twitching motility-mediated biofilm expansion is a coordinated, multicellular behaviour, allowing cells to rapidly colonize surfaces, including implanted medical devices. Although at least 44 proteins are known to be involved in the biogenesis, assembly and regulation of the T4P, with additional regulatory components and pathways implicated, it is unclear how these components and pathways interact to control these processes. In the current study, we used a global genomics-based random-mutagenesis technique, transposon directed insertion-site sequencing (TraDIS), coupled with a physical segregation approach, to identify all genes implicated in twitching motility-mediated biofilm expansion in P. aeruginosa. Our approach allowed identification of both known and novel genes, providing new insight into the complex molecular network that regulates this process in P. aeruginosa. Additionally, our data suggest that the flagellum-associated gene products have a differential effect on twitching motility, based on whether components are intra- or extracellular. Overall the success of our TraDIS approach supports the use of this global genomic technique for investigating virulence genes in bacterial pathogens