Search Results (17)

Antimicrobial fragrances, commonly found in household and personal care products, are frequently detected in water bodies, yet their environmental fate and transformation mechanisms remain inadequately explored. This study investigates the photochemical transformation of cinnamaldehyde (CA), a representative antimicrobial fragrance, and its consequence for toxicological effects. The results showed that under UV irradiation, 94.6% CA was eliminated within 60 min, with a degradation rate of 0.059 min⁻¹. Laser flash photolysis, quenching experiments, and electron paramagnetic resonance spectra identified O₂^•− and ³CA^* as the important species, contributing 29.4% and 33.6%, respectively, to the transformation process. Additionally, singlet oxygen (¹O₂), hydroxyl radicals (^•OH), and solvated electrons (e_aq⁻) were involved in mediating the oxidation reactions. These species facilitated photoionization and oxidation, resulting in the formation of five major transformation products, including cis-cinnamyl aldehyde, cinnamic acid, styrene, 1aH-indeno [1,2-b]oxirene), and 1-Oxo-1H-indene. Most of these products were persistent, and exhibited considerable ecotoxicological risks. Specifically, the cinnamic acid and 1-Oxo-1H-indene caused severe skin irritation, while cinnamic acid induced significant eye irritation. Notably, the transformation products demonstrated sensitizing effects on human skin. This study underscores the overlooked ecotoxicological risks associated with the photochemical transformation of antimicrobial fragrances, revealing their potential to generate potent allergens and other harmful byproducts. Full article

The asymptotic giant branch (AGB) phase, experienced by low- and intermediate-mass stars (LIMSs), plays a crucial role in galaxies due to its significant dust production. Planetary nebulae (PNe) offer a novel perspective, providing valuable insights into the dust production mechanisms and the evolutionary history of LIMSs. We selected a sample of nine PNe from the Large Magellanic Cloud (LMC), likely originating from single stars. By modeling their spectral energy distributions (SEDs) with photoionization techniques, we successfully reproduced the observed photometric data, spectra, and chemical abundances. This approach enabled us to constrain key characteristics of the central stars (CSs), dust, and gaseous nebulae, which were then compared with predictions from stellar evolution models. By integrating observational data across ultraviolet (UV) to infrared (IR) wavelengths, we achieved a comprehensive understanding of the structure of the PNe in our sample. The results of the SED analysis are consistent with evolutionary models and previous studies that focus on individual components of the PN, such as dust or the gaseous nebula. Our analysis enabled us to determine the metallicity, the progenitor mass of the CSs, and the amount of dust and gas surrounding the CSs, linking these properties to the previous AGB phase. The PN phase provides critical insights into the physical processes active during earlier evolutionary stages. Additionally, we found that higher progenitor masses are associated with greater amounts of dust in the surrounding nebulae but lower amounts of gaseous material compared to sources with lower progenitor masses. Full article

Chemosensor technology for trace gases in the air always aims to identify these compounds and then measure their concentrations. For identification, traceable methods are sparse and relate to large appliances such as mass spectrometers. We present a new method that uses the alternative traceable measurement of the ionization energies of trace gases in a way that can be miniaturized and energetically tuned. We investigate the achievable performance. Since tunable UV sources are not available for photoionization, we take a detour via impact ionization with electrons, which we generate using the photoelectric effect and bring to sharp, defined energies on a nanoscale in the air. Electron impact ionization is thus possible at air pressures of up to 900 hPa. The sensitivity of the process reaches 1 ppm and is equivalent to that of classic PID. With sharpened energy settings, substance identification is currently possible with an accuracy of 30 meV. We can largely explain the experimental observations with the known quantum mechanical models. Full article

We present UV photofragmentation studies of the structural isomers paracetamol, 3-Pyridinepropionic acid (3-PPIA) and (R)-(-)-2-Phenylglycine. In particular, we utilized a new laser-based thermal desorption source in combination with femtosecond multiphoton ionization at 343 nm and 257 nm. The continuous nature of our molecule source, combined with the 50 kHz repetition rate of the laser, allowed us to perform these experiments at high throughput. In particular, we present detailed laser intensity dependence studies at both wavelengths, producing 2D mass spectra with highly differential information about the underlying fragmentation processes. We show that UV photofragmentation produces highly isomer-specific mass spectra, and assign all major fragmentation pathways observed. The intensity-dependence measurements, furthermore, allowed us to evaluate the appearance intensities for each fragmentation channel, which helped to distinguish competing from consecutive fragmentation pathways. Full article

The optical and UV properties of radio-quiet (RQ) and radio-loud (RL, relativistically “jetted”) active galactic nuclei (AGN) are known to differ markedly; however, it is still unclear what is due to a sample selection and what is associated with intrinsic differences in the inner workings of their emitting regions. Chemical composition is an important parameter related to the trends of the quasar main sequence. Recent works suggest that in addition to physical properties such as density, column density, and ionization level, strong Feii emitters require very high metal content. Little is known, however, about the chemical composition of jetted radio-loud sources. In this short note, we present a pilot analysis of the chemical composition of low-z radio-loud and radio-quiet quasars. Optical and UV spectra from ground and space were combined to allow for precise measurements of metallicity-sensitive diagnostic ratios. The comparison between radio-quiet and radio-loud was carried out for sources in the same domain of the Eigenvector 1/main sequence parameter space. Arrays of dedicated photo-ionization simulations with the input of appropriate spectral energy distributions indicate that metallicity is sub-solar for RL AGN, and slightly sub-solar or around solar for RQ AGN. The metal content of the broad line-emitting region likely reflects a similar enrichment story for both classes of AGN not involving recent circum-nuclear or nuclear starbursts. Full article

A comparison between the classical gas chromatography (GC) technique with supercritical fluid chromatography (SFC) technology was performed using an essential oil of Citrus limon (lemon) as a model, considering its wide use in the cosmetic world. For the qualitative part, the signal annotation was achieved by mass spectrometry using either an electron ionization (EI) or an atmospheric pressure photoionization (APPI) source. For the quantitative part, GC was hyphenated to a flame ionization detector (GC-FID) and SFC to an ultraviolet detector (SFC-UV). The assay of the major component of citrus oil, i.e., limonene, was carried out by SFC-UV. The similar results obtained between GC-FID and SFC-UV allows SFC-UV to be considered as an alternative to GC-FID for Citrus oil characterization. Then, analyses of an essential oil collection from Citrus fruits were achieved to confirm the potential use of SFC-UV for oil classification in the context of quality control of raw materials in cosmetics. Full article

The issue of the difference between optical and UV properties of radio-quiet and radio-loud (relativistically “jetted”) active galactic nuclei (AGN) is a long standing one, related to the fundamental question of why a minority of powerful AGN possess strong radio emission due to relativistic ejections. This paper examines a particular aspect: the singly-ionized iron emission in the spectral range 4400–5600 Å, where the prominent HI H$\beta$ and [Oiii]$\lambda \lambda$4959,5007 lines are also observed. We present a detailed comparison of the relative intensity of Feii multiplets in the spectral types of the quasar main sequence where most jetted sources are found, and afterwards discuss radio-loud narrow-line Seyfert 1 (NLSy1) nuclei with $\gamma$-ray detection and with prominent Feii emission. An Feii template based on I Zw 1 provides an accurate representation of the optical Feii emission for RQ and, with some caveats, also for RL sources. CLOUDY photoionization simulations indicate that the observed spectral energy distribution can account for the modest Feii emission observed in composite radio-loud spectra. However, spectral energy differences alone cannot account for the stronger Feii emission observed in radio-quiet sources, for similar physical parameters. As for RL NLSy1s, they do not seem to behave like other RL sources, likely because of their different physical properties, that could be ultimately associated with a higher Eddington ratio. Full article

This paper reviews several basic emission properties of the UV emission lines observed in the spectra of quasars and type-1 active galactic nuclei, mainly as a function of the ionization parameter, metallicity, and density of the emitting gas. The analysis exploits a general-purpose 4D array of the photoionization simulations computed using the code CLOUDY, covering ionization parameter in the range ${10}^{-4.5}$–${10}^{+1.0}$, hydrogen density $n_{\mathrm{H}}$$\sim {10}^7$–${10}^{14}$ cm⁻³, metallicity Z between 0.01 and 100 $Z_{\odot }$, and column density in the range ${10}^{21}$–${10}^{23}$ cm⁻². The focus is on the most prominent UV emission lines observed in quasar spectra, namely Nv$\lambda$1240, Siiv$\lambda$1397, Oiv]$\lambda$1402, Civ$\lambda$1549, Heii$\lambda$1640, Aliii$\lambda$1860, Siiii]$\lambda$1892, and Ciii]$\lambda$1909, and on the physical conditions under which electron-ion impact excitation is predicted to be the dominant line producer. Photoionization simulations help constrain the physical interpretation and the domain of applicability of spectral diagnostics derived from measurements of emission line ratios, reputed to be important for estimating the ionization degree, density, and metallicity of the broad line emitting gas, as well as the relative intensity ratios of the doublet or multiplet components relevant for empirical spectral modeling. Full article

The study deals with the primary species, ejected electrons, and guanine radicals, leading to oxidative damage, that is generated in four-stranded DNA structures (guanine quadruplexes) following photo-ionization by low-energy UV radiation. Performed by nanosecond transient absorption spectroscopy with 266 nm excitation, it focusses on quadruplexes formed by folding of GGG(TTAGGG)₃ single strands in the presence of K⁺ ions, TEL21/K⁺. The quantum yield for one-photon ionization (9.4 × 10⁻³) was found to be twice as high as that reported previously for TEL21/Na⁺. The overall population of guanine radicals decayed faster, their half times being, respectively, 1.4 and 6.7 ms. Deprotonation of radical cations extended over four orders of magnitude of time; the faster step, concerning 40% of their population, was completed within 500 ns. A reaction intermediate, issued from radicals, whose absorption spectrum peaked around 390 nm, was detected. Full article

Background: Many planetary nebulae retain significant quantities of molecular gas and dust despite their signature hostile radiation environments and energetic shocks. Photoionization and dissociation by extreme UV and (often) X-ray emission from their central stars drive the chemical processing of this material. Their well-defined geometries make planetary nebulae ideal testbeds for modeling the effects of radiation-driven heating and chemistry on molecular gas in photodissociation regions. Methods: We have carried out IRAM 30m/APEX 12m/ALMA radio studies of the Helix Nebula and its molecule-rich globules, exploiting the unique properties of the Helix to follow up our discovery of an anti-correlation between HNC/HCN line intensity ratio and central star UV Luminosity. Results: Analysis of HNC/HCN across the Helix Nebula reveals the line ratio increases with distance from the central star, and thus decreasing incident UV flux, indicative of the utility of the HNC/HCN ratio as a tracer of UV irradiation in photodissociation environments. However, modeling of the observed regions suggests HNC/HCN should decrease with greater distance, contrary to the observed trend. Conclusion: HNC/HCN acts as an effective tracer of UV irradiation of cold molecular gas. Further model studies are required. Full article

Increasing population and expansion of urban areas are often associated with degradation of aquatic ecosystems. Although water quality is a major concern for worldwide authorities, several emerging contaminants can threaten long term status of aquatic ecosystems and human health. UV filters are widely used in industrial products such as plastics, paints and coatings, to enhance their photo protective properties. Personal care products, such as shampoos, body creams, make-up and sunscreens, used in humans’ daily routine, also comprise a wide variety of chemicals, such as organic UV filters and parabens. Some UV filters are persistent, bioaccumulative and toxic. Parabens prevent bacterial growth and extend products shelf-lives, but they can have endocrine disruption properties. Wastewater is a potential vehicle of UV filters and parabens to the aquatic ecosystems, where they tend to accumulate in suspended sediments. This study investigates the presence of organic UV filters and parabens in Ribeira dos Covões peri-urban catchment, in central mainland Portugal. The catchment has been deeply urbanized over the last decades, due to its proximity to Coimbra city center. Urban areas cover 40% of the catchment land-use and include several health services, such as a hospital, and a relatively large pharmaceutical company. Wastewater is piped and transported into a treatment plant (WWTP) located outside the catchment. The sewer system, however, is sometimes subject to failure, leading to leakages which affect local streams. In September 2018, fluvial sediment samples (0-3 cm depth) were collected in 10 sites across Ribeira dos Covões stream network. The freeze-dried sediment samples were extracted using an accelerated solvent extractor (ASE-350, DIONEX, Germany) method, and analysed for 17 UV filters, 5 parabens and 2 synthetic musks, using an Agilent UHPLC-MS/MS system operating with dopant-assisted atmospheric pressure photoionization (DA-APPI). The results show the presence of methylparaben (10.3 ng/g dw) at the catchment outlet. UV filters were found in sediments from several sites in Ribeira dos Covões. Compounds revealing highest concentrations were octocrylene, quantified in 8 of the 10 sampling sites and reaching 286.3 ng/g dw, and ethylhexyltriazone, quantified in half of the monitored sites in concentrations up to 67.7 ng/g dw. The largest number of compounds and with highest concentrations, were recorded in two stream sections that received wastewater, based on reports from local citizens about sewer pipe leakages. Wastewater contamination can represent a major problem for the good status of aquatic ecosystems in urban environments. Full article

It is of interest to use UV-sulfite based processes to degrade pollutants in wastewater treatment process. In this work, arsenic (As(III)) has been selected as a target pollutant to verify the efficacy of such a hypothesized process. The results showed that As(III) was quickly oxidized by a UV-sulfite system at neutral or alkaline pH and especially at pH 9.5, which can be mainly attributed to the generated oxysulfur radicals. In laser flash photolysis (LFP) experiments (λ_ex = 266 nm), the signals of SO₃^•− and e_aq⁻ generated by photolysis of sulfite at 266 nm were discerned. Quantum yields for photoionization of HSO₃⁻ (0.01) and SO₃²⁻ (0.06) were also measured. It has been established that e_aq⁻ does not react with SO₃²⁻, but reacts with HSO₃⁻ with a rate constant 8 × 10⁷ M⁻¹s⁻¹. Full article

Government regulations and environmental conditions are pushing the development of improved miniaturized gas analyzers for volatile organic compounds. One of the many detectors used for gas analysis is the photoionization detector (PID). This paper presents the design and characterization of a microfluidic photoionization detector (or µPID) fabricated using micro milling and electrical discharge machining techniques. This device has no glue and facilitates easy replacement of components. Two materials and fabrication techniques are proposed to produce a layer on the electrodes to protect from ultraviolet (UV) light and possible signal noise generation. Three different microchannels are tested experimentally and their results are compared. The channel with highest electrode area (31.17 mm²) and higher volume (6.47 µL) produces the highest raw signal and the corresponding estimated detection limit is 0.6 ppm for toluene without any amplification unit. Full article

Resonance enhanced multiphoton ionization (REMPI) is a powerful method for the sensitive determination of polycyclic aromatic hydrocarbons (PAHs) in gaseous mixtures via mass spectrometry (MS). In REMPI, ions are produced by the absorption of at least two photons including defined electronic intermediate states. As a result—unlike other laser-based ionization techniques—spectroscopic selectivity is involved into the ionization process. Nevertheless, these wavelength-dependent ionization rates impede the quantification using REMPI. For this purpose, relative photoionization cross sections (relPICS) give an easy-to-use approach to quantify REMPI-MS measurements. Hereby, the ionization behavior of a single compound was compared to that of a reference substance of a given concentration. In this study, relPICS of selected single-core aromatics and PAHs at wavelengths of 266 nm and 248 nm were determined using two different time-of-flight mass spectrometric systems (TOFMS). For PAHs, relPICS were obtained which showed a strong dependence on the applied laser intensity. In contrast, for single-core aromatics, constant values of relPICS were determined. Deviations of relPICS between both TOFMS systems were found for small aromatics (e.g., benzene), which can be assigned to the differences in UV generation in the particular system. However, the relPICS of this study were found to be in good agreement with previous results and can be used for system-independent quantification. Full article

We suggest that most of the mass in planetary nebulae (PNe) resides in the equatorial region and the spherical envelope and the optically bright lobes of PNe are in fact low-density cavities cleared out by fast outflows and photoionized by UV photons leaked from the torus. The nature of multi-polar PNe is discussed under this framework. Full article