Kinetic studies of gaseous halogen oxide radical reactions implicated in ozone depletion

Increased atmospheric emissions of photolabile halogen-containing species as a result of human activity over the Twentieth Century have had a dramatic impact on atmospheric ozone. This has generated significant scientific interest in understanding the reactivity of halogens in the gas phase. In particular, the self- and cross-reactions of halogen monoxide radicals, XO (where X = F, Cl, Br, I), which are the first-formed intermediates in the reaction of photolytically released halogen atoms with ozone, have been identified as key processes in ozone-depleting events as they initiate reaction cycles that catalytically destroy ozone. Understanding the kinetics of these reactions is therefore crucial to establishing their potential for ozone destruction. These reactions are, however, complex multichannel processes, with both bimolecular and termolecular components contributing to the overall reaction. As some product channels do not contribute to the catalytic destruction of ozone, an accurate determination of the product branching is also of utmost importance for a comprehensive understanding of the atmospheric ozone budget. In this thesis, results from studies of the kinetics of the ClO and BrO self-reactions and of the BrO + ClO cross-reaction, carried out under appropriate atmospheric conditions, are presented. These reactions were studied using laser flash photolysis coupled with UV absorption spectroscopy. This technique adopted the rapid generation of the XO radicals of interest following laser photolysis and monitoring their temporal behaviour via UV absorption spectroscopy facilitated by charge-coupled device (CCD) detection. The use of a CCD detector allowed broadband time-resolved acquisition of spectra, leading to the unequivocal identification of multiple species and to the accurate quantification of their concentrations via the Beer-Lambert law. The desired kinetic information was then obtained from fitting classical or numerical integration simulations to the experimental concentration profiles. Extensive sensitivity analyses of the results obtained were performed to identify the principal sources of uncertainty in these measurements. The results from the present work are compared to those obtained in previous studies and their implications for ozone in the Earth’s atmosphere are discussed

The application of a cavity ring-down spectrometer to measurements of ambient ammonia using traceable primary standard gas mixtures

A correction for the undesirable effects of direct and indirect cross-interference from water vapour on ammonia (NH$_3$) measurements was developed using an optical laser sensor based on cavity ring-down spectroscopy. This correction relied on new measurements of the collisional broadening due to water vapour of two NH$_3$ spectral lines in the near infra-red (6548.6 and 6548.8 cm$^{−1}$), and on the development of novel stable primary standard gas mixtures (PSMs) of ammonia prepared by gravimetry in passivated gas cylinders at 100 μmol mol$^{−1}$. The PSMs were diluted dynamically to provide calibration mixtures of dry and humidified ammonia atmospheres of known composition in the nmol mol$^{−1}$ range and were employed as part of establishing a metrological traceability chain to improve the reliability and accuracy of ambient ammonia measurements. The successful implementation of this correction will allow the extension of this rapid on-line spectroscopic technique to exposure chamber validation tests under controlled conditions and ambient monitoring in the field.We gratefully acknowledge the funding received from the Chemical and Biological Metrology Programme of the UK Department for Business, Innovation and Skills (BIS) and the European Metrology Research Programme (EMRP) of the European Union. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union.This is the author accepted manuscript. The final version is available from Springer via http://dx.doi.org/10.1007/s00340-016-6486-

Kinetic studies of the BrO plus ClO cross-reaction over the range T=246-314 K

The kinetics of the atmospherically important gas phase radical reaction between BrO and ClO have been studied over the temperature range T = 246–314 K by means of laser flash photolysis coupled with UV absorption spectroscopy. Charge-coupled-device (CCD) detection allowed simultaneous monitoring of both free radicals and the OClO product using ‘differential’ spectroscopy, which minimised interference from underlying UV absorbing species. In this way, the total rate coefficient for BrO + ClO → products (1) was measured, along with that for the OClO producing channel of this process BrO + ClO → OClO + Br (1c). These reaction rate coefficients are described by the Arrhenius expressions: k1/cm3 molecule−1 s−1 = (2.5 ± 2.2) × 10−12 exp[(630 ± 240)/T] and k1c/cm3 molecule−1 s−1 = (4.6 ± 3.0) × 10−12 exp[(280 ± 180)/T], where errors are 2σ, statistical only. An extensive sensitivity analysis was performed to quantify the potential additional systematic uncertainties in this work arising from uncertainties in secondary chemistry, absorption cross-sections and precursor concentrations. This analysis identified the reactions of initial and secondarily generated bromine atoms (specifically Br + O3 and Br + Cl2O) as particularly important, along with the reversible combination of ClO with OClO forming Cl2O3. Potential uncertainty in this latter process was used to define the lowest temperature of the present study. Results from this work indicate larger absolute values for k1 and k1c than those reported in previous studies, but a weaker negative temperature dependence for k1c than previously observed, resulting in a branching ratio for channel (1c) with a positive temperature dependence, in disagreement with previous studies. Reaction (1c) is the principal source of OClO in the polar stratosphere and is commonly used in atmospheric models as an indicator of stratospheric bromine chemistry. Thus these measurements might lead to a reinterpretation of modelled stratospheric OClO, which has also been suggested by previous comparisons of observations with atmospheric model studies

ROOOH: A missing piece of the puzzle for OH measurements in low-NO environments?

Abstract. Field campaigns have been carried out with the FAGE (fluorescence assay by gas expansion) technique in remote biogenic environments in the last decade to quantify the in situ concentrations of OH, the main oxidant in the atmosphere. These data have revealed concentrations of OH radicals up to a factor of 10 higher than predicted by models, whereby the disagreement increases with decreasing NO concentration. This was interpreted as a major lack in our understanding of the chemistry of biogenic VOCs (volatile organic compounds), particularly isoprene, which are dominant in remote pristine conditions. But interferences in these measurements of unknown origin have also been discovered for some FAGE instruments: using a pre-injector, all ambient OH is removed by fast reaction before entering the FAGE cell, and any remaining OH signal can be attributed to an interference. This technique is now systematically used for FAGE measurements, allowing the reliable quantification of ambient OH concentrations along with the signal due to interference OH. However, the disagreement between modelled and measured high OH concentrations of earlier field campaigns as well as the origin of the now-quantifiable background OH is still not understood. We present in this paper the compelling idea that this interference, and thus the disagreement between model and measurement in earlier field campaigns, might be at least partially due to the unexpected decomposition of a new class of molecule, ROOOH, within the FAGE instruments. This idea is based on experiments, obtained with the FAGE set-up of the University of Lille, and supported by a modelling study. Even though the occurrence of this interference will be highly dependent on the design and measurement conditions of different FAGE instruments, including ROOOH in atmospheric chemistry models might reflect a missing piece of the puzzle in our understanding of OH in clean atmospheres. </jats:p

Feasibility and safety of PIPAC combined with additional surgical procedures: PLUS study.

PIPAC (Pressurized IntraPeritoneal Aerosol Chemotherapy) is a minimally invasive approach relying on physical principles for improving intraperitoneal drug delivery, including optimizing the homogeneity of drug distribution through an aerosol. Feasibility and safety of the new approach are now consolidated and data on its effectiveness are continuously increasing. Although any surgical procedure associated with PIPAC had always been discouraged due to the high risk of complications, surgical practice is constantly changing: with growing expertise, more and more surgical teams associate PIPAC with surgery. PLUS study is part of the retrospective international cohort studies including 10 centers around the world (India, Italy, France, Germany, Belgium, Russia, Saudi Arabia, Switzerland) and 96 cases of combined approaches evaluated through a propensity score analysis. the procedures most frequently associated with PIPAC were not only adhesiolysis, omentectomy, adnexectomy, umbilical/inguinal hernia repairs, but also more demanding procedures such as intestinal resections, gastrectomy, splenectomy, bowel repair/stoma creation. Although the evidence is currently limited, PLUS study demonstrated that PIPAC associated with additional surgical procedures is linked to an increase of surgical time (p &lt; 0.001), length of stay (p &lt; 0.001) and medical complication rate (p &lt; 0.001); the most frequently reported medical complications were mild or moderate in severity, such as abdominal pain, nausea, ileus and hyperthermia. No difference in terms of surgical complications was registered; neither reoperation or postoperative deaths were reported. these results suggest that PIPAC can be safely combined in expert centers with additional surgeries. Widespread change of practice should be discouraged before the results of ongoing prospective studies are available

Genetic and epigenetic alterations of cdh1 regulatory regions in hereditary and sporadic gastric cancer

E-cadherin is a key player in gastric cancer (GC) and germline alterations of CDH1, its encoding gene, are responsible for Hereditary Diffuse Gastric Cancer (HDGC) syndrome. This study aimed at elucidating the role of genetic variants and DNA methylation of CDH1 promoter and enhancers in the regulation of gene expression. For this purpose, we analyzed genetic variants of the CDH1 gene through Next-Generation Sequencing (NGS) in a series of GC cell lines (NCI-N87, KATO-III, SNU-1, SNU-5, GK2, AKG, KKP) and the corresponding CDH1 expression levels. By bisulfite genomic sequencing, we analyzed the methylation status of CDH1 regulatory regions in 8 GC cell lines, in a series of 13 sporadic GC tissues and in a group of 20 HDGC CDH1-negative patients and 6 healthy controls. The NGS analysis on CDH1 coding and regulatory regions detected genetic alterations in 3 out of 5 GC cell lines lacking functional E-cadherin. CDH1 regulatory regions showed different methylation patterns in patients and controls, GC cell lines and GC tissues, expressing different E-cadherin levels. Our results showed that alterations in terms of genetic variants and DNA methylation patterns of both promoter and enhancers are associated with CDH1 expression levels and have a role in its regulation.This research and its authors were funded by IRCCS IRST (G.T., C.M., R.D. V.A., M.R., F.R., M.C., S.P., G.M., D.C., P.U.) and by FEDER-Fundo Europeu de Desenvolvimento Regional funds through the COMPETE 2020–Operacional Programme for Competitiveness and Internationalization (POCI), Portugal 2020, and by Portuguese funds through FCT–Fundação para a Ciência e a Tecnologia/Ministério da Ciência, Tecnologia e Inovação in the framework of the project “Institute for Research and Innovation in Health Sciences” (POCI-01-0145-FEDER-007274) (C.S.J., R.B.-M., A.A., C.O.). This work was also financed by the project NORTE-01-0145-FEDER-000029 (CANCER)-supported by Norte Portugal Regional Programme (NORTE 2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (ERDF)–project POCI-01-0145-FEDER-016390 (CancelStem) and PTDC/BTM-TEC/30164/2017 (3DChroMe), funded by ERDF, POCI and FCT

CCQM-K90, formaldehyde in nitrogen, 2 μmol mol− 1 Final report

The CCQM-K90 comparison is designed to evaluate the level of comparability of national metrology institutes (NMI) or designated institutes (DI) measurement capabilities for formaldehyde in nitrogen at a nominal mole fraction of 2 μmol mol−1. The comparison was organised by the BIPM using a suite of gas mixtures prepared by a producer of specialty calibration gases. The BIPM assigned the formaldehyde mole fraction in the mixtures by comparison with primary mixtures generated dynamically by permeation coupled with continuous weighing in a magnetic suspension balance. The BIPM developed two dynamic sources of formaldehyde in nitrogen that provide two independent values of the formaldehyde mole fraction: the first one based on diffusion of trioxane followed by thermal conversion to formaldehyde, the second one based on permeation of formaldehyde from paraformaldehyde contained in a permeation tube. Two independent analytical methods, based on cavity ring down spectroscopy (CRDS) and Fourier transform infrared spectroscopy (FTIR) were used for the assignment procedure. Each participating institute was provided with one transfer standard and value assigned the formaldehyde mole fraction in the standard based on its own measurement capabilities. The stability of the formaldehyde mole fraction in transfer standards was deduced from repeated measurements performed at the BIPM before and after measurements performed at participating institutes. In addition, 5 control standards were kept at the BIPM for regular measurements during the course of the comparison. Temporal trends that approximately describe the linear decrease of the amount-of-substance fraction of formaldehyde in nitrogen in the transfer standards over time were estimated by two different mathematical treatments, the outcomes of which were proposed to participants. The two treatments also differed in the way measurement uncertainties arising from measurements performed at the BIPM were propagated to the uncertainty of the trend parameters, as well as how the dispersion of the dates when measurements were made by the participants was taken into account. Upon decision of the participants, the Key Comparison Reference Values were assigned by the BIPM using the largest uncertainty for measurements performed at the BIPM, linear regression without weight to calculate the trend parameters, and not taking into account the dispersion of dates for measurements made by the participant. Each transfer standard was assigned its own reference value and associated expanded uncertainty. An expression for the degree of equivalence between each participating institute and the KCRV was calculated from the comparison results and measurement uncertainties submitted by participating laboratories. Results of the alternative mathematical treatment are presented in annex of this report

Atmospheric isoprene measurements reveal larger-than-expected Southern Ocean emissions

Isoprene is a key trace component of the atmosphere emitted by vegetation and other organisms. It is highly reactive and can impact atmospheric composition and climate by affecting the greenhouse gases ozone and methane and secondary organic aerosol formation. Marine fluxes are poorly constrained due to the paucity of long-term measurements; this in turn limits our understanding of isoprene cycling in the ocean. Here we present the analysis of isoprene concentrations in the atmosphere measured across the Southern Ocean over 4 months in the summertime. Some of the highest concentrations ( >500 ppt) originated from the marginal ice zone in the Ross and Amundsen seas, indicating the marginal ice zone is a significant source of isoprene at high latitudes. Using the United Kingdom Earth System Model we show that current estimates of sea-to-air isoprene fluxes underestimate observed isoprene by a factor >20. A daytime source of isoprene is required to reconcile models with observations. The model presented here suggests such an increase in isoprene emissions would lead to >8% decrease in the hydroxyl radical in regions of the Southern Ocean, with implications for our understanding of atmospheric oxidation and composition in remote environments, often used as proxies for the pre-industrial atmosphere

A metrological approach to improve accuracy and reliability of ammonia measurements in ambient air

The environmental impacts of ammonia (NH$_3$) in ambient air have become more evident in the recent decades, leading to intensifying research in this field. A number of novel analytical techniques and monitoring instruments have been developed, and the quality and availability of reference gas mixtures used for the calibration of measuring instruments has also increased significantly. However, recent inter-comparison measurements show significant discrepancies, indicating that the majority of the newly developed devices and reference materials require further thorough validation. There is a clear need for more intensive metrological research focusing on quality assurance, intercomparability and validations. MetNH3 (Metrology for ammonia in ambient air) is a three-year project within the framework of the European Metrology Research Programme (EMRP), which aims to bring metrological traceability to ambient ammonia measurements in the 0.5–500 nmol mol$^{−1}$ amount fraction range. This is addressed by working in three areas: (1) improving accuracy and stability of static and dynamic reference gas mixtures, (2) developing an optical transfer standard and (3) establishing the link between high-accuracy metrological standards and field measurements. In this article we describe the concept, aims and first results of the project.EMRP MetNH3 (EURAMET

A metrological approach to improve accuracy and reliability of ammonia measurements in ambient air

The environmental impacts of ammonia (NH$_3$) in ambient air have become more evident in the recent decades, leading to intensifying research in this field. A number of novel analytical techniques and monitoring instruments have been developed, and the quality and availability of reference gas mixtures used for the calibration of measuring instruments has also increased significantly. However, recent inter-comparison measurements show significant discrepancies, indicating that the majority of the newly developed devices and reference materials require further thorough validation. There is a clear need for more intensive metrological research focusing on quality assurance, intercomparability and validations. MetNH3 (Metrology for ammonia in ambient air) is a three-year project within the framework of the European Metrology Research Programme (EMRP), which aims to bring metrological traceability to ambient ammonia measurements in the 0.5–500 nmol mol$^{−1}$ amount fraction range. This is addressed by working in three areas: (1) improving accuracy and stability of static and dynamic reference gas mixtures, (2) developing an optical transfer standard and (3) establishing the link between high-accuracy metrological standards and field measurements. In this article we describe the concept, aims and first results of the project.EMRP MetNH3 (EURAMET