37 research outputs found
Investigation of the secondary organic aerosol (SOA) nucleation from α- pinene ozonolysis
Composition of the newly formed secondary organic aerosol (SOA) generated by ozonolysis of the cyclohexene (model precursor) and α-pinene was studied using liquid chromatography coupled to electrospray ionization tandem mass spectrometry (LC-ESI/MSn). SOA was generated in the flow-tube reactor under standard conditions: 20°C and 1 atm. and the reaction time less than 1 min. In an attempt to resolve the current ambiguities, regarding the structure of the α-pinene SOA nucleating agents, analytical methods for analysis of α-acyloxyhydroperoxy aldehydes and high molecular weight (HMW) compounds containing carboxylic group were developed. Both groups of those compounds are currently considered as the potential nucleating agents. However, no analytical evidence proving the presence of α-acyloxyhydroperoxy aldehydes in the SOA samples have been presented. Also, very limited experimental data, indicating that the nucleating agents are acidic oligomers is currently available. The α-acyloxyhydroperoxy aldehydes were analyzed with LC-ESI/MSn for the first time. Analysis of the tandem mass spectra of the α-acyloxyhydroperoxy aldehydes ammonia adducts was used to propose the general fragmentation mechanism, supported by the analysis of the isotopically labeled analogs. The proposed mechanism was used to predict the mass spectrum of the α-acyloxyhydroperoxy aldehydes that could not be synthesized. After analyzing the SOA samples, generated in the flow-tube reactor, it was concluded that α-acyloxyhydroperoxy aldehydes were not formed in significant quantities, and are unlikely to participate in the aerosol nucleation. Direct analytical evidence was found, arguing against the gas-phase nucleation and proving that acidic oligomers are formed in the early stages of SOA formation. Also, based on the acquired experimental data, it was concluded that the reactive uptake of carbonyl compounds is an important growth mechanism for the freshly formed SOA. For the first time, isotopically labeled analog of cyclohexene (cyclohexene-d10) was used to propose the structures for the up-to-date unknown oligomers. The acquired experimental data point out the need for revision of the current α-pinene SOA nucleation mechanism.Skład świeżo powstałego wtórnego aerozolu organicznego (secondary organic aerosol, SOA) został przeanalizowany za pomocą chromatografii cieczowej połączonej z tandemową spektrometrią mas z jonizacją przez elektrorozpylanie (LC-ESI/MSn). SOA został wytworzony w reaktorze przepływowym w standardowych warunkach temperatury i ciśnienia: 20°C i 1 atm. a czas reakcji wynosił < 1 min. Aby rozstrzygnąć obecne niepewności dotyczące struktury zalążków nukleacji SOA powstałego w wyniku ozonolizy α-pinenu, zostały opracowane metody analizy α-acyloksyhydroperoxy aldehydów oraz oligomerów zawierających grupę karboksylową. Obydwa typy związków są obecnie rozważane, jako potencjalne zalążki nukleacji. Jednak, do tej pory nie zostały przedstawione żadne bezpośrednie dowody potwierdzające obecność α-acyloksyhydroperoxy aldehydów w próbkach SOA. Ponadto, tylko niewielka ilość danych wskazuje, iż zalążkami nukleacji są kwasowe oligomery. α-Acyloksyhydroperoxy aldehydy po raz pierwszy zostały przeanalizowane za pomocą LC-ESI/MSn. W wyniku analizy widm fragmentacyjnych został zaproponowany ogólny mechanizm fragmentacji adduktów amonowych α-acyloksyhydroperoxy aldehydów; mechanizm ten został potwierdzony za pomocą analizy izotopowo znaczonych analogów. Zaproponowany mechanizm fragmentacji został wykorzystany żeby przewidzieć widmo masowe α-acyloksyhydroperoxy aldehydów, które nie mogły być zsyntezowane. W próbkach SOA wytworzonych w reaktorze przepływowym, α-acyloxyhydroperoxy aldehydy nie zostały wykryte w znaczących ilościach i prawdopodobnie nie brały udziału w procesie nukleacji aerozolu. Otrzymane wyniki wskazują, iż nukleacja prawdopodobnie nie zachodzi w fazie gazowej. Jednocześnie, zostało udowodnione, że kwasowe oligomery są wytwarzane już na wczesnych etapach formowania SOA. Stwierdzono także, iż absorpcja związków karbonylowych w wyniku formowania się oligomerów jest ważnym mechanizmem wzrostu cząstek aerozolu na czesnych etapach jego powstawania. Po raz pierwszy, izotopowo znaczony prekursor (cykloheksen-d10) został wykorzystany do zaproponowania struktur do tej pory nieznanych oligomerów. Zidentyfikowane oligomery najprawdopodobniej powstały w wyniku reakcji związków karbonylowych. Wyniki przedstawione w tej pracy wskazują, iż obecnie zaproponowany mechanizm nukleacji powinien zostać zaktualizowany
Modification of emission properties of ZnO layers due to plasmonic near-field coupling to Ag nanoislands
A simple fabrication method of Ag nanoislands on ZnO films is presented.
Continuous wave and time-resolved photoluminescence and transmission are
employed to investigate modifications of visible and UV emissions of ZnO
brought about by coupling to localized surface plasmons residing on Ag
nanoislands. The size of the nanoislands, determining their absorption and
scattering efficiencies, is found to be an important factor governing plasmonic
modification of optical response of ZnO films. The presence of the Ag
nanoislands of appropriate dimensions causes a strong (threefold) increase in
emission intensity and up to 1.5 times faster recombination. The experimental
results are successfully described by model calculations within the Mie theory.Comment: 14 pages, 5 figure
Catalytic Removal of NOx on Ceramic Foam-Supported ZnO and TiO2 Nanorods Ornamented with W and V Oxides
Energy consumption steadily increases and energy production is associated with many
environmental risks, e.g., generating the largest share of greenhouse gas emissions. The primary gas
pollution concern is CO2, CH4, and nitrogen oxides (NOx). Environmental catalysis plays a pivotal
role in NOx mitigation (DeNOx). This study investigated, for the first time, a collection of ceramic
foams as potential catalyst support for selective catalytic NOx reduction (SCR). Ceramic foams could
be an attractive support option for NOx removal. However, we should functionalize the surface of
raw foams for such applications. A library of ceramic SiC, Al2O3, and ZrO2 foams ornamented with
nanorod ZnO and TiO2 asWand V oxide support was obtained for the first time. We characterized
the surface layer coating structure using the XPS, XRF and SEM, and TEM microscopy to optimize
the W to V molar ratio and examine NO2 mitigation as the SCR model, which was tested only
very rarely. Comparing TiO2 and ZnO systems reveals that the SCR conversion on ZnO appeared
superior vs. the conversion on TiO2, while the SiC-supported catalysts were less efficient than Al2O3
and ZrO2-supported catalysts. The energy bands in optical spectra correlate with the observed
activity rank
Transcatheter mitral valve repair and replacement. Expert consensus statement of the Polish Cardiac Society and the Polish Society of Cardiothoracic Surgeons
<i>cis-</i>Pinonic Acid Oxidation by Hydroxyl Radicals in the Aqueous Phase under Acidic and Basic Conditions: Kinetics and Mechanism
Aqueous-phase
oxidation of <i>cis-</i>pinonic acid (CPA)
by hydroxyl radicals (OH) was studied using a relative rate technique
under acidic and basic conditions. Liquid chromatography (LC) coupled
to the negative electrospray ionization (ESI) quadrupole tandem mass
spectrometry (MS/MS) was used to monitor the concentrations of CPA
and reference compounds. The measured second order reaction rate coefficients
of CPA with OH were: 3.6 ± 0.3 × 10<sup>9</sup> M<sup>–1</sup> s<sup>–1</sup> (pH 2) and 3.0 ± 0.3 × 10<sup>9</sup> M<sup>–1</sup> s<sup>–1</sup> (pH 10) - combined uncertainties
are 2σ. These results indicated that the lifetimes of CPA in
the atmosphere are most likely independent from the aqueous-phase
pH. LC-ESI/MS/MS was also used to tentatively identify the CPA oxidation
products. Formation of carboxylic acids with molecular weight (MW)
216 Da (most likely C<sub>10</sub>H<sub>16</sub>O<sub>5</sub>) and
MW 214 Da (C<sub>10</sub>H<sub>14</sub>O<sub>5</sub>) was confirmed
with LC-ESI/MS/MS. When the initial CPA concentration was increased
from 0.3 to 10 mM, formation of additional products was observed with
MW 188, 200, 204, and 232 Da. Hydroperoxy, hydroxyl and carbonyl-substituted
CPA derivatives were tentatively identified among the products. Similar
products were formed by the CPA oxidation by OH in the gas-phase,
at the air–water interface as well as in the solid phase (dry
film). Formation of the stable adduct of CPA and H<sub>2</sub>O<sub>2</sub> was also observed when the reaction mixture was evaporated
to dryness and redissolved in water. Acquired mass spectrometric data
argues against formation of oligomers
Properties of Elasto-Hydrodynamic Oil Film in Meshing of Harmonic Drive Gears
Among the essential issues facing designers of strain wave gears, the provision for correct lubrication should be of paramount importance. The present paper presents the results of research on elasto-hydrodynamic oil film in meshing of a harmonic drive with an involute tooth profile. The research was carried out based on theoretical models developed by Dowson and Higginson. For the discussed structural problem, results of the study are presented graphically in the form of static characteristics of the oil film. Correct operation regimes were determined for two different oils. The paper also provides a review of information concerning the design and principle of operation of strain wave transmission
The effect of oil feeding type and oil grade on the oil film bearing capacity
Two types of hydrodynamically lubricated plain journal bearings were subject to examination differing in the method used to feed them with oil. The first type was fed from a lubrication pocket and the second from the bearing face side. Mathematical models were developed with two-way oil flow allowing to determine the oil film bearing capacity, the maximum pressure, the maximum temperature, and the film oil minimum height for given position of journal relative to solid bush. Static characteristics were developed used in the further course of the study to compare operating parameters of the considered types of bearings. Another issue considered in the paper is the effect of oil VG grade on bearing performance with conditions of oil feeding taken into account and results of the research presented
Properties of Elasto-Hydrodynamic Oil Film in Meshing of Harmonic Drive Gears
Among the essential issues facing designers of strain wave gears, the provision for correct lubrication should be of paramount importance. The present paper presents the results of research on elasto-hydrodynamic oil film in meshing of a harmonic drive with an involute tooth profile. The research was carried out based on theoretical models developed by Dowson and Higginson. For the discussed structural problem, results of the study are presented graphically in the form of static characteristics of the oil film. Correct operation regimes were determined for two different oils. The paper also provides a review of information concerning the design and principle of operation of strain wave transmission