A white cell based broadband transient UV-vis absorption spectroscopy with pulsed laser photolysis reactors for chemical kinetics under variable temperatures and pressures.

UV-vis spectroscopy is widely used for kinetic studies in physical chemistry, as species' absolute cross-sections are usually less sensitive to experimental conditions (i.e., temperature and pressure).

Acetonyl Peroxy and Hydroperoxy Self- and Cross-Reactions: Temperature-Dependent Kinetic Parameters, Branching Fractions, and Chaperone Effects.

The temperature-dependent kinetic parameters, branching fractions, and chaperone effects of the self- and cross-reactions between acetonyl peroxy (CHC(O)CHO) and hydro peroxy (HO) have been studied using pulsed laser photolysis coupled with infrared (IR) wavelength-modulation spectroscopy and ultraviolet absorption (UVA) spectroscopy. Two IR lasers simultaneously monitored HO and hydroxyl (OH), while UVA measurements monitored CHC(O)CHO. For the CHC(O)CHO self-reaction ( = 270-330 K), the rate parameters were determined to be = (1.

Conformer-Dependent Chemistry: Experimental Product Branching of the Vinyl Alcohol + OH + O Reaction.

The concentration of formic acid in Earth's troposphere is underestimated by detailed chemical models compared to field observations. Phototautomerization of acetaldehyde to its less stable tautomer vinyl alcohol, followed by the OH-initiated oxidation of vinyl alcohol, has been proposed as a missing source of formic acid that improves the agreement between models and field measurements. Theoretical investigations of the OH + vinyl alcohol reaction in excess O conclude that OH addition to the α carbon of vinyl alcohol produces formaldehyde + formic acid + OH, whereas OH addition to the β site leads to glycoaldehyde + HO.

Yields of HONO and HOONO Products from the Reaction of HO and NO Using Pulsed Laser Photolysis and Mid-Infrared Cavity-Ringdown Spectroscopy.

The reaction of HO with NO is one of the most important steps in radical cycling throughout the stratosphere and troposphere. Previous literature experimental work revealed a small yield of nitric acid (HONO) directly from HO + NO. Atmospheric models previously treated HO + NO as radical recycling, but inclusion of this terminating step had large effects on atmospheric oxidative capacity and the concentrations of HONO and ozone (O), among others.

From COVID-19 to future electrification: Assessing traffic impacts on air quality by a machine-learning model.

The large fluctuations in traffic during the COVID-19 pandemic provide an unparalleled opportunity to assess vehicle emission control efficacy. Here we develop a random-forest regression model, based on the large volume of real-time observational data during COVID-19, to predict surface-level NO, O, and fine particle concentration in the Los Angeles megacity. Our model exhibits high fidelity in reproducing pollutant concentrations in the Los Angeles Basin and identifies major factors controlling each species.

Pressure and Temperature Dependencies of Rate Coefficients for the Reaction OH + NO + M → Products.

The OH + NO reaction is a critically important process for radical chain termination in the atmosphere with a major impact on the ozone budgets of the troposphere and stratosphere. Rate constants for the reaction of OH + NO + M → products have been measured under conditions relevant to the upper troposphere/lower stratosphere with a laser photolysis-laser-induced fluorescence (LP-LIF) technique augmented by in situ optical spectroscopy for quantification of [NO]. The experiments are carried out over the temperature range of 230-293 K and the pressure range 50-750 Torr of N and air and as a function of [O].

Acetonyl Peroxy and Hydro Peroxy Self- and Cross-Reactions: Kinetics, Mechanism, and Chaperone Enhancement from the Perspective of the Hydroxyl Radical Product.

Pulsed laser photolysis coupled with infrared (IR) wavelength modulation spectroscopy and ultraviolet (UV) absorption spectroscopy was used to study the kinetics and branching fractions for the acetonyl peroxy (CHC(O)CHO) self-reaction and its reaction with hydro peroxy (HO) at a temperature of 298 K and pressure of 100 Torr. Near-IR and mid-IR lasers simultaneously monitored HO and hydroxyl, OH, respectively, while UV absorption measurements monitored the CHC(O)CHO concentrations. The overall rate constant for the reaction between CHC(O)CHO and HO was found to be (5.

Temperature Dependence of the Reaction of Chlorine Atoms with CHOH and CHCHO.

Rate constants of the reactions Cl + CHOH → CHOH + HCl ( k) and Cl + CHCHO → CHC(O) + HCl ( k) were measured at 100 Torr over the temperature range 230.3-297.1 K.

Temperature Dependence Study of the Kinetics and Product Yields of the HO + CHC(O)O Reaction by Direct Detection of OH and HO Radicals Using 2f-IR Wavelength Modulation Spectroscopy.

The HO + CHC(O)O reaction consists of three product channels: CHC(O)OOH + O (R1a), CHC(O)OH + O (R1b), and OH + CHC(O)O + O (R1c). The overall rate constant ( k) and product yields (α, α, and α) were determined over the atmospherically relevant temperature range of 230-294 K at 100 Torr in N. Time-resolved kinetics measurements were performed in a pulsed laser photolysis experiment in a slow flow cell by employing simultaneous infrared (IR) and ultraviolet (UV) absorption spectroscopy.

Source Apportionment of Ambient Methane Enhancements in Los Angeles, California, To Evaluate Emission Inventory Estimates.

Rapid increase in atmospheric methane (CH) mixing ratios over the past century is attributable to the intensification of human activities. Information on spatially explicit source contributions is needed to develop efficient and cost-effective CH emission reduction and mitigation strategies to addresses near-term climate change. This study collected long-term ambient CH measurements at Mount Wilson Observatory (MWO) in Los Angeles, California, to estimate the annual CH emissions from the portion of Los Angeles County that is within the South Coast Air Basin (SCLA).

Reaction kinetics of OH + HNO under conditions relevant to the upper troposphere/lower stratosphere.

The OH initiated oxidation of HNO3 in the UT/LS plays an important role in controlling the O3 budget, removing HOx radicals whilst driving NOx/y partitioning chemistry by yielding NO3 radicals: OH + HNO3 → H2O + NO3. In this paper, k1(T, P) was measured using OH (A ← X) Laser Induced Fluorescence (LIF) and the data was modelled over the 223-298 K temperature and 25-750 Torr pressure ranges, using the modified Lindemann-Hinshelwood expression , where k0 = 5.2 × 10-14 exp(200/T) cm3 s-1, k2 = 8.

Background levels of methane in Mars' atmosphere show strong seasonal variations.

Variable levels of methane in the martian atmosphere have eluded explanation partly because the measurements are not repeatable in time or location. We report in situ measurements at Gale crater made over a 5-year period by the Tunable Laser Spectrometer on the Curiosity rover. The background levels of methane have a mean value 0.

Matrix-Isolated Infrared Absorption Spectrum of CH2IOO Radical.

The peroxyiodomethyl radical, CH2IOO, was generated in cryogenic matrices using tandem supersonic nozzles. One hyperthermal nozzle decomposes diiodomethane (CH2I2) to generate intense beams of CH2I radicals, while the second nozzle continuously deposits O2/argon (Ar) on the matrix at 10 K. The CH2I and O2 in the Ar matrix react to produce the target peroxy radical (CH2IOO).

Rate Constant for the OH + CO Reaction at Low Temperatures.

Rate constants for the reaction of OH + CO → products (1) have been measured using laser photolysis/laser-induced fluorescence (LP/LIF) over the temperature range 193–296 K and at pressures of 50–700 Torr of Ar and N2. The reaction was studied under pseudo-first-order conditions, monitoring the decay of OH in the presence of a large excess of CO. The rate constants can be expressed as a combination of bimolecular and termolecular components.

VUV photoionization cross sections of HO2, H2O2, and H2CO.

The absolute vacuum ultraviolet (VUV) photoionization spectra of the hydroperoxyl radical (HO2), hydrogen peroxide (H2O2), and formaldehyde (H2CO) have been measured from their first ionization thresholds to 12.008 eV. HO2, H2O2, and H2CO were generated from the oxidation of methanol initiated by pulsed-laser-photolysis of Cl2 in a low-pressure slow flow reactor.

Equilibrium constant for the reaction ClO + ClO ↔ ClOOCl between 250 and 206 K.

The chlorine peroxide molecule, ClOOCl, is an important participant in the chlorine-catalyzed destruction of ozone in the stratosphere. Very few laboratory measurements have been made for the partitioning between monomer ClO and dimer ClOOCl at temperatures lower than 250 K. This paper reports absorption spectra for both ClO and ClOOCl when they are in equilibrium at 1 atm and temperatures down to 206 K.

Measuring rate constants for reactions of the simplest Criegee intermediate (CH2OO) by monitoring the OH radical.

While generating the CH2OO molecule by reacting CH2I with O2, significant amounts of the OH radical were observed by laser-induced fluorescence. At least two different processes formed OH. A fast process was probably initiated by a reaction of vibrationally hot CH2I radicals.

Cavity ringdown spectroscopy of the hydroxy-methyl-peroxy radical.

We report vibrational and electronic spectra of the hydroxy-methyl-peroxy radical (HOCH2OO(•) or HMP), which was formed as the primary product of the reaction of the hydroperoxy radical, HO2(•), and formaldehyde, HCHO. The ν1 vibrational (OH stretch) spectrum and the à ← X̃ electronic spectrum of HMP were detected by infrared cavity ringdown spectroscopy (IR-CRDS), and assignments were verified with density functional calculations. The HMP radical was generated in reactions of HCHO with HO2(•).

Midlatitude atmospheric OH response to the most recent 11-y solar cycle.

The hydroxyl radical (OH) plays an important role in middle atmospheric photochemistry, particularly in ozone (O(3)) chemistry. Because it is mainly produced through photolysis and has a short chemical lifetime, OH is expected to show rapid responses to solar forcing [e.g.

Detection of the far-IR ν12 bending level in propargyl: a complete set of fundamentals for an important radical.

Propargyl (HCCCH(2)) radicals have been generated by expanding precursors through a supersonic pyrolysis nozzle, and their infrared (IR) absorption spectra have been recorded in a rare gas matrix. Besides the 10 vibrational modes observed in our previous studies, this investigation detected the HCCCH(2) X̃ (2)B(1) in-plane bending mode (ν(12)) at 344.2 (±0.

Kinetics of n-butoxy and 2-pentoxy isomerization and detection of primary products by infrared cavity ringdown spectroscopy.

The primary products of n-butoxy and 2-pentoxy isomerization in the presence and absence of O(2) have been detected using pulsed laser photolysis-cavity ringdown spectroscopy (PLP-CRDS). Alkoxy radicals n-butoxy and 2-pentoxy were generated by photolysis of alkyl nitrite precursors (n-butyl nitrite or 2-pentyl nitrite, respectively), and the isomerization products with and without O(2) were detected by infrared cavity ringdown spectroscopy 20 μs after the photolysis. We report the mid-IR OH stretch (ν(1)) absorption spectra for δ-HO-1-C(4)H(8)•, δ-HO-1-C(4)H(8)OO•, δ-HO-1-C(5)H(10)•, and δ-HO-1-C(5)H(10)OO•.

Medical intelligence article: assessing the impact on global climate from general anesthetic gases.

Although present in the atmosphere with a combined concentration approximately 100,000 times lower than carbon dioxide (i.e., the principal anthropogenic driver of climate change), halogenated organic compounds are responsible for a warming effect of approximately 10% to 15% of the total anthropogenic radiative forcing of climate, as measured relative to the start of the industrial era (approximately 1750).

Atmospheric chemistry of isoflurane, desflurane, and sevoflurane: kinetics and mechanisms of reactions with chlorine atoms and OH radicals and global warming potentials.

The smog chamber/Fourier-transform infrared spectroscopy (FTIR) technique was used to measure the rate coefficients k(Cl + CF(3)CHClOCHF(2), isoflurane) = (4.5 ± 0.8) × 10(-15), k(Cl + CF(3)CHFOCHF(2), desflurane) = (1.