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Isoprene has the highest emission into Earth’s atmosphere of any nonmethane hydrocarbon. Atmospheric processing of alkenes, including isoprene, via ozonolysis leads to the formation of zwitterionic reactive intermediates, known as Criegee intermediates (CIs). Direct studies have revealed that reactions involving simple CIs can significantly impact the tropospheric oxidizing capacity, enhance particulate formation, and degrade local air quality. Methyl vinyl ketone oxide (MVK-oxide) is a four-carbon, asymmetric, resonance-stabilized CI, produced with 21 to 23% yield fromisoprene ozonolysis, yet its reactivity has not been directly studied. We present direct kinetic measurements of MVK-oxide reactions with key atmospheric species using absorption spectroscopy. Direct UV-Vis absorption spectra from two independent flow cell experiments overlap with the molecular beam UV-Vis-depletion spectra reported recently [M. F. Vansco, B. Marchetti, M. I. Lester, J. Chem. Phys. 149, 44309 (2018)] but suggest different conformer distributions under jetcooled and thermal conditions. Comparison of the experimental lifetime herein with theory indicates only the syn-conformers are observed; anti-conformers are calculated to be removed much more rapidly via unimolecular decay. We observe experimentally and predict theoretically fast reaction of syn-MVK-oxide with SO₂ and formic acid, similar to smaller alkyl-substituted CIs, and by contrast, slow removal in the presence of water. We determine products through complementary multiplexed photoionization mass spectrometry, observing SO₃ and identifying organic hydroperoxide formation from reaction with SO₂ and formic acid, respectively. The tropospheric implications of these reactions are evaluated using a global chemistry and transport model.

Methacrolein oxide (MACR-oxide) is a four-carbon, resonance-stabilized Criegee intermediate produced from isoprene ozonolysis, yet its reactivity is not well understood. This study identifies the functionalized hydroperoxide species, 1-hydroperoxy-2-methylallyl formate (HPMAF), generated from the reaction of MACR-oxide with formic acid using multiplexed photoionization mass spectrometry (MPIMS, 298 K = 25 °C, 10 torr = 13.3 hPa). Electronic structure calculations indicate the reaction proceeds via an energetically favorable 1,4-addition mechanism. The formation of HPMAF is observed by the rapid appearance of a fragment ion at m/z 99, consistent with the proposed mechanism and characteristic loss of HO2 upon photoionization of functional hydroperoxides. The identification of HPMAF is confirmed by comparison of the appearance energy of the fragment ion with theoretical predictions of its photoionization threshold. The results are compared to analogous studies on the reaction of formic acid with methyl vinyl ketone oxide (MVK-oxide), the other four-carbon Criegee intermediate in isoprene ozonolysis.

Methanol is a benchmark for understanding tropospheric oxidation, but is underpredicted by up to 100% in atmospheric models. Recent work has suggested this discrepancy can be reconciled by the rapid reaction of hydroxyl and methylperoxy radicals with a methanol branching fraction of 30%. However, for fractions below 15%, methanol underprediction is exacerbated. Theoretical investigations of this reaction are challenging because of intersystem crossing between singlet and triplet surfaces – ∼45% of reaction products are obtained via intersystem crossing of a pre-product complex – which demands experimental determinations of product branching. Here we report direct measurements of methanol from this reaction. A branching fraction below 15% is established, consequently highlighting a large gap in the understanding of global methanol sources. These results support the recent high-level theoretical work and substantially reduce its uncertainties. The reaction of hydroxyl and methylperoxy radicals has recently been suggested as the source of missing methanol in the remote troposphere. Here, the authors present direct experimental measurements demonstrating the reaction leads to further underprediction of modelled methanol.

Isoprene has the highest emission into Earth’s atmosphere of any nonmethane hydrocarbon. Atmospheric processing of alkenes, including isoprene, via ozonolysis leads to the formation of zwitterionic reactive intermediates, known as Criegee intermediates (CIs). Direct studies have show that reactions involving simple CIs can significantly impact the tropospheric oxidizing capacity, enhance particulate formation, and degrade local air quality. Methyl vinyl ketone oxide (MVK-oxide) is a four-carbon, asymmetric, resonance-stabilized CI, produced with 21 to 23% yield from isoprene ozonolysis, yet its reactivity has not been directly studied. We present direct kinetic measurements of MVK-oxide reactions with key atmospheric species using absorption spectroscopy. Direct UV-Vis absorption spectra from two independent flow cell experiments overlap with the molecular beam UV-Vis-depletion spectra reported recently [M. F. Vansco, B. Marchetti, M. I. Lester,J. Chem. Phys.149, 44309 (2018)] but suggest different conformer distributions under jet-cooled and thermal conditions. Comparison of the experimental lifetime herein with theory indicates only thesyn-conformers are observed;anti-conformers are calculated to be removed much more rapidly via unimolecular decay. We observe experimentally and predict theoretically fast reaction ofsyn-MVK-oxide with SO2and formic acid, similar to smaller alkyl-substituted CIs, and by contrast, slow removal in the presence of water. We further confirm products through complementary multiplexed photoionization mass spectrometry, observing SO3 and identifying organic hydroperoxide formation from reaction with SO2 and formic acid, respectively. The tropospheric implications of these reactions are evaluated using a global chemistry and transport model.

Spatial Modulated Quantitative Spectroscopy (SMoQS) is a spectroscopic technique that works in the spatial frequency domain, capable of recovering in-vitro optical properties throughout the visible, and near infrared wavelength range (430nm–1050nm). The challenges in screening for Melanoma in the clinic in a non-invasive fashion has motivated the translation of SMoQS into a clinical viable device, which is able to recover high fidelity in-vivo optical properties rapidly under operating constraints in the clinic, while accounting for the layered anatomy of skin. This thesis presents the process of SMoQS' clinical translation and the quantification of its performance and stability in terms of recovered optical properties. In addition, we describe a method of generating a device calibration file in the visible and near infrared range. Finally, we present results obtained from in-vivo clinical SMoQS measurements on areas of high pigmentation and associated normal skin of the human skin. Optical property and chromophore concentration results obtained using this device is in agreement with the literature.

Background Green tea ( Camellia sinesis ) has been studied extensively in adults living with obesity. The consumption of green tea has been investigated for body weight control, with or without exercise. Objectives This review aims to summarize the potential efficacy and safety of green tea in weight reduction. Design A systematic review was conducted in two databases PubMed And Web of Science to identify the relevant clinical studies published between 2016 And 2024. Randomized controlled trials and quasi-experimental studies that assessed the effect of green tea consumption on body weight control were included. Results Fourteen studies were identified. Three studies investigated the effect of green tea consumption without concurrent exercise. Meanwhile, eleven studies investigated the combined effect of green tea and exercise on body weight, body mass index (BMI), waist circumference and waist-hip ratio. Eleven studies (78.5%) showed that green tea supplementation is effective in reducing weight and BMI, with nine of them combined exercise. More research is warranted to standardize the dosage and duration of interventions. A few cases of mild gastric discomfort were reported in two studies. According to tertiary databases (Natural medicines and Lexicomp), several potential drug interactions with green tea have been identified. The interactions are dose-related, though an exact upper and lower threshold of green tea dosage are lacking. Conclusions The majority of clinical studies shown that green tea can lower body weight and BMI in adults with obesity, in particular combined with regular exercise. Green tea is generally safe, though hepatotoxicity has been reported in a dose and duration-dependent manner following consumption of concentrated green tea extracts. It is recommended to consult healthcare professionals prior as green tea may interact with other commonly used Western medications.