@conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/100362, title ="Does the reaction of HO₂ with NO produce HONO₂ and HOONO", author = "Mertens, Laura A. and Allen, Hannah M.", pages = "PHYS-519", month = "March", year = "2015", url = "https://resolver.caltech.edu/CaltechAUTHORS:20191218-144653179", note = "© 2015 American Chemical Society.", revision_no = "10", abstract = "HO_x (HO₂ and OH) and NO_x (NO₂ and NO) radicals are key intermediates in chem. throughout the atm.; the HO_x and NO_x cycles catalyze ozone depletion in the stratosphere and ozone and photochem. smog prodn. in the troposphere. Interconversion within the HO_x family and within the NO_x family happens continuously, partially through the reaction of HO₂ and NO to form OH and NO₂. Since these radicals are continually recycled, even a small branching yield of nitric acid (HONO₂) from the reaction of HO₂ with NO would impact radical concns. predicted in the troposphere and stratosphere, by cumulatively sequestering radicals in a stable reservoir species. Butkovskaya et al. obsd. a small yield of HONO₂ from the reaction of HO₂ with NO (0.5 ˆat 1 atm and 298 K) in a turbulent flow reactor using Chem.-Ionization Mass Spectrometry. We investigated this reaction by an alternative method: detecting the HONO₂ - as well as its weakly bound isomer HOONO - with Pulsed-Cavity Ringdown spectroscopy. HO₂ radicals were produced by Pulsed Laser Photolysis of Cl₂ in a slow flow cell, in the presence of methanol or formaldehyde. Addn. of 700 torr of CO prevented unwanted HONO₂ formation from the reaction of OH and NO₂. Our expts. provide a complementary approach, allowing detection of products spectroscopically on short time-scales in the absence of any wall reactions. Our results raise doubts about the magnitude of the HONO₂ yields obsd. by Butovskaya et al.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/100358, title ="Reactions of atmospheric peroxy radicals studied by synchrotron VUV multiplexed photoionization mass spectrometry", author = "Dodson, Leah G. and Shen, Linhan", pages = "PHYS-556", month = "March", year = "2015", url = "https://resolver.caltech.edu/CaltechAUTHORS:20191218-140316314", note = "© 2015 American Chemical Society.", revision_no = "10", abstract = "Peroxy radicals are key intermediates in the oxidn. chem. of both anthropogenic and biogenic Volatile Org. Compds.(VOCs) in the troposphere. These species are central in the formation of photochem. smog and org. aerosols, and can be formed from abstraction reactions or from addn. reactions with unsatd. hydrocarbons. Lab. studies of the kinetics of peroxy radical reactions are complicated by the many competing self- and cross-reactions that typically occur. The large no. of possible products, esp. chain-propagating radical channels, further complicates the chem. Here we describe recent expts. using time-resolved photoionization mass spectrometry (PIMS) with ionization by VUV synchrotron radiation. This method provides a powerful, highly sensitive technique for studying the product branching ratios and reaction rates, by selective time-resolved detection of many of the reactants, intermediates, and primary products. We report investigations of peroxy radical reactions in a laser-photolysis low-pressure flow cell expt. that utilizes tunable VUV radiation generated at the Advanced Light Source synchrotron at the Lawrence Berkeley Lab., coupled to the Sandia multiplexed PIMS app. We have performed expts. on the reactions of the acetyl peroxy radicals, as well as the selfreaction of the Et peroxy radical. We are able to det. relative product yields based on measurements of abs. radical concns., new abs. photoionization cross sections, with the aid of kinetic modeling.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/48327, title ="Laboratory experiments of HO_2 reactions with peroxy radicals using infrared kinetic spectroscopy (IRKS)", author = "Hui, Aileen O. and Grieman, Frederick J.", pages = "PHYS 95", month = "August", year = "2014", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140811-133839521", note = "© 2014 American Chemical Society.", revision_no = "12", abstract = "The reaction of HO_2 with acetyl peroxy radical, CH_3C(O)O_2, has been suggested to proceed via three channels [1]:(a) HO_2 + CH_3C(O)O_2 → CH_3C(O)O_2H + O_2(b) HO_2 + CH_3C(O)O_2 → CH_3C(O)OH + O_3(c) HO_2 + CH_3C(O)O_2 → CH_3C(O)O + OH + O_2Channel (c) is of particular interest not only because of the lack of prodn. of ozone, but also the formation of the hydroxyl radical, OH, a key oxidizing radical in the earth's atm. The results from several independent studies [2,3,4] have shown that the branching ratio of (c) is close to 0.40. Although the results show strong evidence that channel (c) is a significant branch of the reaction of acetyl peroxy radical with HO_2, all expts. were only done at room temp. (298 K) and none of the expts. used techniques that allowed for the measurement of either of the two reacting species. Another concern is that the overall reaction rates of acetyl peroxy radical with HO_2 obtained by the expts. have shown large discrepancies. Furthermore, there is very little information on the temp. dependence of this reaction at upper troposphere temps. The results have led to upper and lower bound ests. by the JPL Data Evaluation panel that differ by almost an order of magnitude. The current study has employed a powerful method called IR Kinetic Spectroscopy (IRKS) for studying radical reactions. In the presented work, this technique is used to study the consumption of HO2 by CH_3C(O)O_2. Specifically, the kinetic rate consts. of this reaction is detd. as a function of temp. (220 to 298 K) and pressure (50 to 400 torr) by simultaneously measuring the disappearance of HO_2 using near-IR spectroscopy and of CH_3C(O)O_2 using UV spectroscopy at a wavelength where HO_2 does not absorb.[1] Hasson, A. S., Tyndall, G. S., Orlando, J. A, 2004, 108 (28), 5979-5989.[2] Crawford, M. A., Wallington, T. J., Szente, J. J., Maricq, M. A, 1999, 103 (3), 365-378.[3] Dillon, T. And Crowley, J. Discuss., 2008, 8, 7111-7148.[4] Moortgat, G. K., Veyret, B., Lesclaux, R. 1989, 160 (4) 18, 443-447.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/48583, title ="Pressure and temperature dependences of rate coefficients for the reaction OH + NO_2 + M → products", author = "Liu, Yingdi and Sander, Stanley P.", pages = "ENVR 420", month = "August", year = "2014", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140815-074943119", note = "© 2014 American Chemical Society.", revision_no = "10", abstract = "The OH + NO_2 reaction is a critically important process for radical chain termination in the atm. with a major impact on the ozone budgets of the troposphere and stratosphere. Rate consts. for the reaction of OH + NO_2 + → products have been measured under conditions relevant to the upper troposphere/lower stratosphere with a Pulsed Laser Photolysis - Pulsed Laser Induced Fluorescence technique augmented by in situ optical spectroscopy for quantification of [NO_2]. The expts. are carried out over the temp. range of 230K - 330K and the pressure range 40-800 Torr of air and N_2. The reaction was studied under pseudo first-order conditions, monitoring the decay of OH in the presence of a large excess of NO_2. The obsd. pressure and temp. dependences are analyzed to quantify the falloff behavior and to derive parameters for Troe falloff expressions. The atm. implications are discussed.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/48314, title ="Temperature dependent branching ratios of HONO_2 and HOONO from HO_x and NO_x cross reactions found using pulsed cavity-\u200bringdown spectroscopy", author = "Mertens, Laura A. and Okumura, Mitchio", pages = "PHYS 468", month = "August", year = "2014", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140811-131530295", note = "© 2014 American Chemical Society.", revision_no = "14", abstract = "The HO_x (HO_2 and OH) and NO_x (NO and NO_2) cycles have major roles in both ozone loss in the stratosphere and pollution from hydrocarbon oxidn. in the troposphere. Two of the central reactions in the atm. are OH + NO_2 -> HONO_2 and HO_2 + NO -> OH + NO_2.. Formation of stable compds., like HNO_3, by chain termination steps decrease radical concns. in the stratosphere and troposphere and provide sinks for both HO_x and NO_x. We employed pulsed-laser-photolysis (PLP) to generate radicals in a temp.-controlled slow flow cell and mid-IR detection of intermediates and products in real time using cavity-ringdown spectroscopy (CRDS). We have investigated the yields for HONO_2 and HOONO products, extending our previous work on the OH + NO_2 reaction at room temp. Our expts. also shed light on the branching ratio of HONO_2 from HO_2 + NO.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/45314, title ="Kinetics and product yields of the acetyl peroxy + HO_2 radical reaction studied by photoionization mass spectrometry", author = "Dodson, Leah G. and Shen, Linhan", pages = "ENVR-98", month = "March", year = "2014", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140429-131752018", note = "© 2014 American Chemical Society.", revision_no = "18", abstract = "The acetyl peroxy radical (CH_3C(O)O_2) is a key intermediate in the oxidn. of carbonyl-contg. hydrocarbons in\nthe troposphere. Reaction of acetyl peroxy radicals with HO_2 has been suggested as a source of OH radicals\nin low-NO_x conditions. Previous work on this reaction obsd. only two product channels forming (1) peracetic\nacid and (2) acetic acid. Recent expts. have shown that there is a third channel that generates the radicals OH\nand acetoxy: CH_3C(O)O_2 + HO_2 → (1) CH_3C(O)OOH + O_2 (2) CH_3C(O)OH + O_3 (3) CH_3C(O)O + O_2 + OH\nThis last pathway to OH formation would then contribute to the apparent isoprene OH recycling suggested by\ndiscrepancies between atm. models and field observations of OH. There have, however, been significant\ndisagreements among expts. on the yield of OH in this reaction. We report our preliminary studies of acetyl\nperoxy reaction with itself and HO_2. Expts. were conducted at the Advanced Light Source synchrotron at the\nLawerence Berkeley National Lab. using tunable VUV ionizing radiation coupled to the Sandia National Lab.\npulsed-laser-photolysis multiplexed photoionization mass spectrometer to detect time-resolved photofragmets of\nreactants, intermediates, and products. From these results, we report new values for the branching fractions of\nthe three product channels in the acetyl peroxy + HO_2 radical reaction.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33431, title ="Low temperatures and pressure dependence study of OH and CO reaction", author = "Liu, Yingdi and Sander, Stanley P.", pages = "PHYS-131", month = "August", year = "2012", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120822-074655130", revision_no = "14", abstract = "OH radical and CO reaction is of crucial importance in the atmospheres of Mars and Earth. In this work, the reaction is studied under pseudo first-order conditions, monitoring the decay of OH by laser-induced fluorescence in the presence of a large excess of CO. We measured rate coeffs. for the reaction of OH with CO using laser photolysis/laser-induced fluorescence in 180K - 295K temp. under 100 to 200 torr. The pressure dependence study is ranging from 50 to 800 torr with Ar, He or N2 as bath gas. The biexponential decay of OH signal is obsd. and it is analyzed to derive information about the equil. const. for reaction: OH + CO ↔HOCO.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33270, title ="Gas phase reactions of the hydroperoxyl radical HO_2 with carbonyl compounds", author = "Okumura, M. and Sander, S. P.", month = "December", year = "2010", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120816-130547267", note = "© 2012 American Chemical Society.", revision_no = "14", abstract = "The hydroperoxyl radical HO2 is a key member of the hydrogen (HOx) radical family and is present throughout the\nenvironment. It is often the dominant HOx species throughout the atm., where its chem. influences ozone concns. and\nair pollution. Simple carbonyl compds. such as formaldehyde, acetaldehyde, and acetone are among the most abundant\nreactive orgs. in the free troposphere. Their primary degrdn. paths; reaction with OH and photolysis. Reactions of HO2\nwith carbonyls in the gas phase are believed to proceed through a hydrogen bonded adduct. The adduct can then\nundergo an intramol. rearrangement to form a peroxy radical (see figure). The reaction of HO2 with formaldehyde,\nHCHO, has been well studied, yet the spectroscopic evidence for the rearrangement lies in a broad, featureless UV\nspectrum. The reaction of HO2 with acetone, however, was found not to proceed at room temp., and its significance in\nthe atm. was thus not considered. Recent theor. calcns., however, predict that HO2 may react at lower temps. relevant\nto the free troposphere, conditions which favor adduct formation. The computations suggest that this reaction may in fact\nbe another important sink for acetone near the tropopause. Here we report spectroscopic evidence for formation of the\nhydroxy-Me peroxyl radical, the intermediate formed from reaction of HO2 with HCHO. We observe both the mid-IR OH\nstretch band, and the characteristic A-X near IR electronic band of the peroxyl radical, and compare to calcns. In a\nsecond set of expts., we obtain equil. data on the HO2 + acetone reaction using the IR-Kinetic Spectroscopy (IRKS)\ninstrument at the NASA Jet Propulsion Lab. Using diode laser spectroscopy to detect HO2, we det. the DrH and DrS.\nThese results shed light on the atm. relevance of this reaction for carbonyl loss in the atm.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33264, title ="Isoflurane, desflurane, and sevoflurane and global climate change: Atmospheric chemistry and environmental impact of inhaled anesthetics", author = "Sulbaek Andersen, M. P. and Karpichev, B.", month = "December", year = "2010", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120816-111919047", note = "© 2012 American Chemical Society.", revision_no = "13", abstract = "The atm. chem. of isoflurane, desflurane and sevoflurane has been investigated using FTIR/smog chamber and laser\nphotolysis/laser induced fluorescence techniques. The rates of reactions with OH radicals and Cl atoms, have been\nmeasured and the products resulting from the OH radicals and chlorine atom initiated oxidn. have been identified. For\nthe first time, measured absorption cross sections of the anesthetics were weighted by an instantaneous cloudy-sky\nradiative forcing calcd. for a model atm., allowing for a more accurate evaluation of the global warming potentials for this\nselection of important medical compds. The results will be discussed with respect to the impact of inhaled anesthetics on\nthe radiative forcing of climate change.", }