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The apportionment of the contribution of wood smoke emitted particles to the total concentration of particulate matter in a region has been greatly aided by the development of new analytical methods. These analytical methods quantitatively determine organic marker compounds unique to wood combustion such as levoglucosan and dehydroabietic acid. These markers have generally been determined in 24-hour averaged samples. We have developed an instrument based on the collection of particles on an inert filter, desorption of the organic material in an inert atmosphere with subsequent GC separation and MS detection of the desorbed compounds. The GC-MS Organic Aerosol Monitor (OAM) instrument has been used in three field studies. An unexpected finding from these studies was the quantification of the contribution of secondary organic aerosols from gases present in wood smoke in addition to primary wood smoke emitted particles. The identification of this secondary material was made possible by the collection of hourly averaged data that allowed for the time patterns of black carbon, organic material, and wood smoke marker compounds to be included and compared in a Positive Matrix Factorization (PMF) analysis. Most of the organic markers associated with wood smoke (levoglucosan, stearic acid and dehydroabietic acid) are associated with primary wood smoke emissions, but a fraction of the levoglucosan and stearic acid are also associated with secondary organic material formed from gaseous precursors in wood smoke. Additionally, this secondary material was shown to be present in each in of the three urban area where wood smoke burning occurs. There is a need for additional studies to better understand the contribution of secondary particulate formation from both urban and wildfires.iImplications/i: This paper presents results from three field studies which show that in addition to the formation of primary particulate matter from the combustion of wood smoke and secondary particulate matter is also formed from the gaseous compounds emitted with the wood smoke. This material is identified in the studies of wood combustion reported here by the identification and quantification of specific organic marker compounds related to wood combustion and is shown to and represents a contributor nearly as large as the primary emitted material and better quantifying the impact of wood combustion on airborne fine particulate matter.

During August and September 2012, a study was conducted to determine the sources of PM2.5 adjacent to the I-710 Long Beach Freeway. The site is directly affected by the emissions from heavy diesel traffic flowing from major container ports about 10 km south of the sampling site. Hourly average data were obtained for particulate species including PM2.5, black carbon and UV absorbing carbon, EC, fine particulate nonvolatile and semi-volatile organic material (NVOM and SVOM), sulfate, nitrate, chloride, ammonium ion, and Na ion, and for related factors including O3, CO, NOX, SO2, and total traffic flow on the I-710. A total of 520 hourly averaged data sets with 15 measured variables were analyzed by EPA-PMF v5.0. The data were best described by a 10-factor solution. Based on the composition and diurnal patterns of the factors, they were assigned to three diesel-related factors (two of which appeared to represent traffic from the ports and one general freeway diesel factor), a light-duty, spark-ignition vehicle-related factor, three secondary factors (one of which was associated with O3 formation processes), and three factors dominated by sulfate, SO2, and chloride, respectively. The diurnal patterns for these last three factors are strongly correlated. Meteorological and refinery upset data indicate that they are associated with emissions from a nearby refinery. The results of the PMF analysis were combined with nephelometer light scattering, corrected for coarse particle scattering and estimated aerosol water content in a multilinear regression analysis to identify visibility degradation sources. Major contributors were the aerosol water content, and the secondary PMF factors associated with either Nitrate and NVOM or NVOM and SVOM. The use of hourly average data made possible the identification of factors associated with gasoline vehicle emissions and both port and non-port diesel emissions.Implications: Hourly averaged data were obtained for PM2.5, its components and factors related to primary emissions and the formation of secondary material at a near freeway sampling location adjacent to the I-710 freeway just south of the Long Beach Boulevard entrance and 10 km north of the Ports of Long Beach and Los Angeles. The major objective of the study was to determine the impact of traffic from the ports at the monitoring site. This manuscript reports on the PMF analysis of the data set. Factors related to both diesel traffic originating from the ports and diesel traffic from non-port origins were identified. The diesel traffic originating from the ports was responsible for 9% of the total traffic and 95% of the BC measured at the sampling site. The non-port diesel traffic was responsible for 15% of the total traffic and 5% of the BC. While the Port 1 diesel traffic coming from the ports contributed a large fraction of the BC, this source contributed only 2% of the CO and 5% of the NOX at the sampling site. The impact of these traffic sources on light scattering was also small. Analysis of sources of sulfate and SO2 at the sampling site indicated that these species did not come from port activities of ships at or approaching the port, but rather from upset flare events at a nearby oil refinery.

Carboxylic acids have been detected in particles collected in various regions of the world. Here, we use experiments and Born–Oppenheimer molecular dynamics simulations to better understand the mechanism of particle formation from gas phase mixtures of formic acid (HCOOH), (CH3)3N, and water vapor. A flow reaction cell coupled to two scanning mobility particle sizers has been used to measure particle size, absolute number of particles and kinetics of particle formation. Experimental results show that the addition of (CH3)3N to a mixture of HCOOH and water vapor results in a dramatic increase in particle formation. Simulation results indicate that the ion-pair formation on the water surface involves direct proton transfer between HCOOH and (CH3)3N. The HCOO—··(CH3)3NH+ ion-pair remains at the air–water interface due to hydrogen bonding and the interfacial hydration shell. This experiment-theory study shows the formation of aerosol particles from the organic acid-amine interactions, which may aid in understanding the role of organics in haze and cloud droplet formation and nanoparticle growth. Carboxylic acids and amines constitute a big part of aerosol particles but the precise details of their formation mechanism are still under investigation. Here, the authors use Born–Oppenheimer molecular dynamics simulations combined with experiments to measure the morphology and kinetics of particle formation.

Exposure to high concentrations of particulate matter has been linked to an increase in asthma, heart problems, and death. This link has increased the importance of understanding particle formation...

Sulfur dioxide (SO2) is an important precursor for formation of atmospheric sulfate aerosol and acid rain. We present an instrument using Broad Band Cavity Enhanced Absorption Spectroscopy (BBCEAS) for the measurement of SO2 with a minimum limit of detection of 0.6 ppbv using the spectral range 305.5–312 nm and an averaging time of 60 seconds. The instrument consists of high reflectivity mirrors (0.9984 at 310 nm) and a deep UV light source. The effective absorption path length of the instrument is 610 m in a 0.957 m base length. Published reference absorption cross-sections were used to fit and retrieve the SO2 concentrations and were compared to a diluted standard for SO2. The comparison was well correlated, R2 = 0.9985 with a correlation slope of 1.01.

A study was conducted on the Brigham Young University campus during January and February 2015 to identify winter-time sources of fine particulate material in Utah Valley, Utah. Fine particulate mass and components and related gas-phase species were all measured on an hourly averaged basis. Light scattering was also measured during the study. Included in the sampling was the first-time source apportionment application of a new monitoring instrument for the measurement of fine particulate organic marker compounds on an hourly averaged basis. Organic marker compounds measured included levoglucosan, dehydroabietic acid, stearic acid, pyrene, and anthracene. A total of 248 hourly averaged data sets were available for a positive matrix factorization (PMF) analysis of sources of both primary and secondary fine particulate material. A total of nine factors were identified. The presence of wood smoke emissions was associated with levoglucosan, dehydroabietic acid, and pyrene markers. Fine particulate secondary nitrate, secondary organic material, and wood smoke accounted for 90% of the fine particulate material. Fine particle light scattering was dominated by sources associated with wood smoke and secondary ammonium nitrate with associated modeled fine particulate water.The identification of sources and secondary formation pathways leading to observed levels of PM

Particulate matter (PM) is among the most harmful air pollutants to human health, but due to its complex chemical composition is poorly characterized. A large fraction of PM is composed of organic compounds, but these compounds are not regularly monitored due to limitations in current sampling and analysis techniques. The Organic Aerosol Monitor (GC-MS OAM) combines a collection device with thermal desorption, gas chromatography and mass spectrometry to quantitatively measure the carbonaceous components of PM on an hourly averaged basis. The GC-MS OAM is fully automated and has been successfully deployed in the field. It uses a chemically deactivated filter for collection followed by thermal desorption and GC-MS analysis. Laboratory tests show that detection limits range from 0.2 to 3 ng for 16 atmospherically relevant compounds, with the possibility for hundreds more. The GC-MS OAM was deployed in the field for semi-continuous measurement of the organic markers, levoglucosan, dehydroabietic acid, and polycyclic aromatic hydrocarbons (PAHs) from January to March 2015. Results illustrate the significance of this monitoring technique to characterize the organic components of PM and identify sources of pollution.

During August and September 2012, a study was conducted to determine the sources of PM2.5 adjacent to the I-710 Long Beach Freeway. The site is directly affected by the emissions from heavy diesel traffic flowing from major container ports about 10 km south of the sampling site. Hourly average data were obtained for particulate species including PM2.5, black carbon and UV absorbing carbon, EC, fine particulate nonvolatile and semi-volatile organic material (NVOM and SVOM), sulfate, nitrate, chloride, ammonium ion, and Na ion, and for related factors including O3, CO, NOX, SO2, and total traffic flow on the I-710. A total of 520 hourly averaged data sets with 15 measured variables were analyzed by EPA-PMF v5.0. The data were best described by a 10-factor solution. Based on the composition and diurnal patterns of the factors, they were assigned to three diesel-related factors (two of which appeared to represent traffic from the ports and one general freeway diesel factor), a light-duty, spark-ignition vehicle-related factor, three secondary factors (one of which was associated with O3 formation processes), and three factors dominated by sulfate, SO2, and chloride, respectively. The diurnal patterns for these last three factors are strongly correlated. Meteorological and refinery upset data indicate that they are associated with emissions from a nearby refinery. The results of the PMF analysis were combined with nephelometer light scattering, corrected for coarse particle scattering and estimated aerosol water content in a multilinear regression analysis to identify visibility degradation sources. Major contributors were the aerosol water content, and the secondary PMF factors associated with either Nitrate and NVOM or NVOM and SVOM. The use of hourly average data made possible the identification of factors associated with gasoline vehicle emissions and both port and non-port diesel emissions.

Recent experimental results show that the kinetics of some radical–radical reactions important for atmospheric pollution formation are faster when a radical–molecule complex forms as one step in the reaction mechanism. Calculated radical–molecule equilibria are needed to accurately describe the concentrations of complexes formed in these experiments as well as in the atmosphere. Here we report calculation of the equilibrium constant for complexation of hydroperoxy (HO2·) and 2-hydroxyethylperoxy radicals (HOCH2CH2O2·) with one water molecule by directly calculating the canonical partition function of the reactant and product species. We demonstrate the accuracy of the calculation using formation of the water dimer as a test case. Ab initio calculations provide the binding energy, rotational constants, and vibrational frequencies of both monomers and complexes. We demonstrate the failure of the harmonic approximation in the partition function for describing the low-frequency vibrational modes of the complexes. Instead, we model one dissociative hydrogen bond mode using a Lennard-Jones 6–3 potential and the other low-frequency vibrational modes using one- and twofold hindered rotors. The contributions of weakly bound states of the long-range dipole–dipole potential (Lennard-Jones 6–3) and of vibration–rotation coupling are not as important as the contribution of twofold hindered rotors. We also discuss methods for including multiple hydrogen-bonding configurations (local minima) when calculating equilibrium constants for formation of complexes.

Portable and compact instruments for separating and detecting organic compounds are needed in the field for environmental studies. This is especially the case for pollution studies as in-field detection of organic compounds helps identify sources of pollution. Here we describe the development of a compact GC and simple pre-concentrator coupled to a MS detector. This simple system can easily be incorporated into portable instrumentation. Combining the pre-concentrator and compact column has the advantage of decoupling separation from manual injection and enhances separation of environmentally relevant polar organic compounds, such as levoglucosan. A detection limit of 2.2 ng was obtained for levoglucosan. This simple design has the potential to expand the use of gas chromatography as a routine in-field separation technique.

Peroxy radicals can complex with water vapor. These complexes affect tropospheric chemistry. In this study, β-HEP (hydroxyethyl peroxy radical) serves as a model system for investigating the effect of water vapor on the kinetics and product branching ratio of the self-reaction of peroxy radicals. The self-reaction rate coefficient was determined at 274–296 K with water vapor between 1.0 × 1015 and 2.5 × 1017 molecules cm−3 at 200 Torr total pressure by slow-flow laser flash photolysis coupled with UV time-resolved spectroscopy and long-path, wavelength modulated, diode-laser spectroscopy. The overall self-reaction rate constant expressed as the product of both a temperature-dependent and water vapor–dependent term is , suggesting formation of a β-HEP-H2O complex is responsible for the increase in the self-reaction rate coefficient with increasing water concentration. Complex formation is supported by computational results identifying three local energy minima for the β-HEP-H2O complex. As the troposphere continues to get warmer and wetter, more of the peroxy radicals present will be complexed with water. Investigating the effect of water vapor on kinetics of atmospherically relevant radicals and determining the effects of these altered kinetics on tropospheric ozone concentrations is thus important.

A significant need exists to better characterize air pollution and its sources. This especially pertains to fine particulate matter (PM2.5). PM2.5 is chemically complex and its sources of emission and secondary production are highly variable. PM2.5 complexity is largely due to the organic fraction, which ranges from 10 to 90% of its total mass. However, the organic compounds in PM2.5 have generally not been monitored in the field due to limitations in available sampling techniques. A source apportionment study was conducted at the Neil Armstrong Academy campus, 5194 Highbury Pkwy, West Valley City, UT 84120, during January and February 2016. Among the objectives of the study was to identify winter-time sources of fine particulate material in West Valley City, Utah. Fine particulate mass and components, particulate organic marker and related gas phase species were all measured on an hourly average basis. The following hourly averaged data were used in the Positive Matrix Factorization (PMF) analysis, fine particulate mass, cations and anions, carbonaceous material, organic marker compounds, gas phase species including NOX, NO2 and CO and mass spectrometric measurements of gas phase methanol and C8 aromatics. A total of 557 hourly averaged data sets with 23 components were available for an EPA Positive Matrix Factorization (v5.0) analysis of the data set. The data were best described by a solution with 7 factors. Two of the factors were associated with emissions from mobile sources, diesel and automotive. One factor was associated with wood smoke emissions. Three factors were associated with the formation of secondary fine particulate material. The larger of the three was associated with the production of secondary nitrate and accounted for 70% of the PM2.5, while the other two were associated with secondary formation of particulate organic material from wood smoke associated gas phase organic compounds but accounted for only 3% of the total PM2.5 mass. The final factor was associated with fine particulate sulfate and SO2. Meteorological back-trajectory data clearly indicted the source was associated with emissions from a copper smelter to the west of the sampling site.

The US. Environmental Protection Agency (EPA) has proposed a new secondary standard based on visibility in urban areas. The proposed standard will be based on light extinction, calculated from 24-hr averaged measurements. It would be desirable to base the standard on a shorter averaging time to better represent human perception of visibility This could be accomplished by either an estimation of extinction from semicontinuous particulate matter (PM) data or direct measurement of scattering and absorption. To this end we have compared 1-hr measurements of fine plus coarse particulate scattering using a nephelometer along with an estimate of absorption from aethalometer measurements. The study took place in Lindon, UT, during February and March 2012. The nephelometer measurements were corrected for coarse particle scattering and compared to the Filter Dynamic Measurement System (FDMS) tapered element oscillating microbalance monitor (TEOM) PM2.5 measurements. The two measurements agreed with a mass scattering coefficient of 3.3 +/- 0.3 m2/g at relative humidity below 80%. However at higher humidity, the nephelometer gave higher scattering results due to water absorbed by ammonium nitrate and ammonium sulfate in the particles. This particle-associated water is not measured by the FDMS TEOM. The FDMS TEOM data could be corrected for this difference using appropriate IMPROVE protocols if the particle composition is known. However a better approach may be to use a particle measurement system that allows for semicontinuous measurements but also measures particle bound water Data are presented from a 2003 study in Rubidoux, CA, showing how this could be accomplished using a Grimm model 1100 aerosol spectrometer or comparable instrument.

The results of an ab initio study on a family of hydroxy peroxy radical–water complexes formed from the oxidation of E-2-hexenal, which constitutes an important component of biogenic atmospheric emissions, are reported. Binding energies for the β-hydroxy-γ-peroxy hexanal (β- and γ-positions are relative to the carbonyl) radical–water complex and the γ-hydroxy-β-peroxy hexanal radical–water complex are predicted to be to 3.8 and 3.6 kcal/mol, respectively, computed at the MP2/6-311++G(2d,2p)//B3LYP/6-311++G(2d,2p) computational level. Natural bond orbital reveals that conventional hydrogen bonding between the water and the hydroxy and aldehyde functional groups of the radical are primarily responsible for the stability of the complex. It can be shown that the peroxy moiety contributes very little to the stability of the radical–water complexes. Thermochemistry calculations reveal estimated equilibrium constants that are comparable to those recently reported for several hydroxy isoprene radical–water complexes. The results of this report suggest that the hexanal peroxy radical–water complexes are expected to play a significant role in the complex chemistry of the atmosphere. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Exposure to fine particulate air pollution has been implicated as a risk factor for cardiopulmonary disease and mortality. Proposed biological pathways imply that particle-induced pulmonary and systemic inflammation play a role in activating the vascular endothelium and altering vascular function. Potential effects of fine particulate pollution on vascular function are explored using controlled chamber exposure and uncontrolled ambient exposure. Research subjects included four panels with a total of 26 healthy nonsmoking young adults. On two study visits, at least 7 days apart, subjects spent 3 hr in a controlled-exposure chamber exposed to 150-200 microg/m3 of fine particles generated from coal or wood combustion and 3 hr in a clean room, with exposure and nonexposure periods alternated between visits. Baseline, postexposure, and post-clean room reactive hyperemia-peripheral arterial tonometry (RH-PAT) was conducted. A microvascular responsiveness index, defined as the log of the RH-PAT ratio, was calculated. There was no contemporaneous vascular response to the few hours of controlled exposure. Declines in vascular response were associated with elevated ambient exposures for the previous 2 days, especially for female subjects. Cumulative exposure to real-life fine particulate pollution may affect vascular function. More research is needed to determine the roles of age and gender, the effect of pollution sources, the importance of cumulative exposure over a few days versus a few hours, and the lag time between exposure and response.

A human subject exposure chamber, designed to hold six to eight subjects, coupled to an approximately 30-m3 Teflon reaction bag was designed and built to provide exposures that mimic the production and photochemical oxidation of atmospheric pollutants resulting from the combustion of coal or wood from a stove. The combustion products are introduced into the Teflon bag under atmospheric conditions. Photochemical oxidation of this mixture is accomplished by exposure to tropospheric sun-like radiation from an array of ultraviolet and black lamps. The aerosol in the Teflon reaction bag is then transferred into the exposure room to maintain a constant, lower exposure level. Continuous and semicontinuous monitoring of the gas and particulate matter (PM) pollution in the exposure room and the reaction bag is accomplished using a suite of instruments. This suite of instruments allows for the measurement of the concentrations of total and nonvolatile PM, nitric oxide, nitrogen dioxide, carbon monoxide, carbon dioxide, and ozone. The concentration of the particles was monitored by an R&P tapered element oscillating microbalance monitor. The chemical composition of the PM and its morphological characterization is accomplished by collecting samples in filter packs and conducting ion chromatography, elemental X-ray fluorescence, and scanning electron microscopy analyses. The concentration and composition of emissions from combustion of wood and coal is described. The results of this study suggest that although the bulk compositions of particulate emissions from the combustion of coal or wood in a stove have many similarities, the wood smoke aerosol is photochemically reactive, whereas the coal smoke aerosol is not.

Rates of reactions can be expressed as dn/dt = kf(n), where n is moles of reaction, k is a rate constant, and f(n) is a function of the properties of the sample. Instrumental measurement of rates requires c(dn/dt) = ckf(n), where c is the proportionality constant between the measured variable and the rate of reaction. When the product of instrument time constant, τ, and k is ≪ 1, the reaction is much slower than the time response of the instrument and measured rates are unaffected by instrument response. When τ k 1, the reaction rate and instrument response rate are sufficiently comparable that measured rates are significantly affected by instrument response and correction for instrument response must be done to obtain accurate reaction kinetics. This paper describes a method for simultaneous determination of τ, k, c, and instrument baseline by fitting equations describing the combined instrument response and rate law to rates observed as a function of time. When τ cannot be neglected, correction for instrument response has previously been done by truncating early data or by use of the Tian equation. Both methods can lead to significant errors that increase as τk increases. Inclusion of instrument baseline as a fitting parameter significantly reduced variability in k and c compared with use of measured instrument baselines. The method was tested with data on the heat rate from acid-catalyzed hydrolysis of sucrose collected with three types of calorimeters. In addition, to demonstrate the generality of this method of data analysis, equations including τ, k, c, and instrument baseline are derived for the relation between the reaction rate and the observed rate for first order, second order (first in each reactant), nth order in one reactant, autocatalytic, Michaelis–Menten kinetics, and the Ng equation. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 53–61, 2011

Herein we report an extensive ab initio study on the existence of eight beta-hydroxy isoprene peroxy radical-water complexes. Binding energies calculated at the MP2(full)/6-311++G(2d,2p)//CCSD(T)/6-311++G(d,p) level of theory range between 3.85 and 5.66 kcal mol(-1). The results of natural bond orbital calculations are presented to help rationalize complex formation. Atmospheric lifetimes, equilibrium constants, heats of formation, and the relative abundance of complexed to uncomplexed peroxy radicals are also reported and discussed.

The gas phase reactions of CH3O2 + CH3O2, HO2 + HO2, and CH3O2 + HO2 in the presence of water vapor have been studied at temperatures between 263 and 303 K using laser flash photolysis coupled with UV time-resolved absorption detection at 220 and 260 nm. Water vapor concentrations were quantified using tunable diode laser spectroscopy operating in the mid-IR. The HO2 self-reaction rate constant is significantly enhanced by water vapor, consistent with what others have reported, whereas the CH3O2 self-reaction and the cross-reaction (CH3O2 + HO2) rate constants are nearly unaffected. The enhancement in the HO2 self-reaction rate coefficient occurs because of the formation of a strongly bound (6.9 kcal mol(-1)) HO2 x H2O complex during the reaction mechanism where the H2O acts as an energy chaperone. The nominal impact of water vapor on the CH3O2 self-reaction rate coefficient is consistent with recent high level ab initio calculations that predict a weakly bound CH3O2 x H2O complex (2.3 kcal mol(-1)). The smaller binding energy of the CH3O2 x H2O complex does not favor its formation and consequent participation in the methyl peroxy self-reaction mechanism.

The rate coefficients for the reactions OH + ClOOCl --HOCl + ClOO (eq 5) and OH + Cl2O --HOCl + ClO (eq 6) were measured using a fast flow reactor coupled with molecular beam quadrupole mass spectrometry. OH was detected using resonance fluorescence at 309 nm. The measured Arrhenius expressions for these reactions are k5 = (6.0 +/- 3.5) x 10(-13) exp((670 +/- 230)/T) cm(3) molecule(-1) s(-1) and k6 = (5.1 +/- 1.5) x 10(-12) exp((100 +/- 92)/T) cm(3) molecule(-1) s(-1), respectively, where the uncertainties are reported at the 2sigma level. Investigation of the OH + ClOOCl potential energy surface using high level ab initio calculations indicates that the reaction occurs via a chlorine abstraction from ClOOCl by the OH radical. The lowest energy pathway is calculated to proceed through a weak ClOOCl-OH prereactive complex that is bound by 2.6 kcal mol(-1) and leads to ClOO and HOCl products. The transition state to product formation is calculated to be 0.59 kcal mol(-1) above the reactant energy level. Inclusion of the OH + ClOOCl rate data into an atmospheric model indicates that this reaction contributes more than 15% to ClOOCl loss during twilight conditions in the Arctic stratosphere. Reducing the rate of ClOOCl photolysis, as indicated by a recent re-examination of the ClOOCl UV absorption spectrum, increases the contribution of the OH + ClOOCl reaction to polar stratospheric loss of ClOOCl.

The existence of a series of organic peroxy radical-water complexes [CH3O2.H2O (methyl peroxy); CH3CH2O2.H2O (ethyl peroxy); CH3C(O)O2.H2O (acetyl peroxy); CH3C(O)CH2O2.H2O (acetonyl peroxy); CH2(OH)O2.H2O (hydroxyl methyl peroxy); CH2(OH)CH2O2.H2O (2-hydroxy ethyl peroxy); CH2(F)O2.H2O (fluoro methyl peroxy); CH2(F)CH2O2.H2O (2-fluoro ethyl peroxy)] is evaluated using high level ab initio calculations. A wide range of binding energies is predicted for these complexes, in which the difference in binding energies can be explained by examination of the composition of the R group attached to the peroxy moiety. The general trend in binding energies has been determined to be as follows: fluorine approximately alkylcarbonylalcohol. The weakest bound complex, CH3O2.H2O, is calculated to be bound by 2.3 kcal mol-1, and the strongest, the CH2(OH)O2.H2O complex, is bound by 5.1 kcal mol-1. The binding energy of the peroxy radical-water complexes which contain carbonyl and alcohol groups indicates that these complexes may perturb the kinetics and product branching ratios of reactions involving these complexes.

Perturbations of the vibrational and electronic energy levels of isolated HO 2 by formation of a doubly hydrogen bound association complex with H 2 O 2 have been investigated using ab initio calculations. Minimum potential energy surfaces for a six-membered and five-membered ring structures are found. The binding energy, vibrational frequencies and low lying electronic excited states are predicted for the lowest energy structure of the complex and are calibrated by calculations of the separated monomers. The lowest energy conformation of the complex is found to be bound by 7.9 kcal mol −1 . We find that complexation with H 2 O 2 blue shifts HO 2 electronic excited states by ∼0.1 eV and redshifts H 2 O 2 states by ∼0.1 eV. Two additional, though exceedingly weak, electronic transitions are found to borrow oscillator strength from the ground state of the hydrogen bonded complex. The enthalpy and entropy of formation of the complex is estimated to be Δ H 0 (270 K)=-35.8 kJ mol -1 and Δ S 0 (270 K)=-138.3 J mol -1 K -1 . The existence of a HO 2 –H 2 O 2 complex is discussed in terms of its potential role in atmospheric photochemistry and laboratory kinetic studies.

The article to which this erratum refers was published in Int J Chem Kinet 2015, 47, 395-409 (2015) (10.1002/kin.20917).

Flash photolysis combined with UV time-resolved spectroscopy has been utilized to investigate the composite UV cross section for methyl formate peroxy (CH3OC(O)O2 and O2CH2OC(O)H) between 210 and 3...

The photodissociation of Br2CO around 267 nm has been studied by time-of-flight mass spectroscopy and ion velocity imaging. The atomic (Br and Br*) and molecular products (Br2 and BrCO) are detected via multiphoton ionization with the same laser. The results show that the molecule dissociates into (1) Br(fast)+Br(slow)+CO via an asynchronously concerted three-body decay process for both ground and spin–orbit excited bromine atoms, (2) BrCO(A)+Br, and (3) Br2+CO, the molecular elimination channel. The translational energy distributions of bromine atoms from reaction (1) are bimodal. For both spin–orbit states the anisotropy parameters differ clearly for slow and fast bromine atoms, where the β values for slow bromine atoms decrease relative to those for fast atoms. The β values for the Br2 elimination channel almost reach the low limit of −1. Taking into account the translational energy and angular distributions of these reactions, an asynchronously concerted decay mechanism could be proposed for the three...

The strong binding energies for radical-molecule complexes allow these unique systems to influence both the photochemical and reaction pathways for both chemical and atmospherically important reactions. This Minireview summarizes the work that has been presented in the literature and also introduces new radical-molecule complexes that may play important roles in new chemistry.

FTIR spectroscopy/UV laser flash photolysis has been used to examine the reaction of chlorine atoms with methyl formate (CH 3 OC(O)H) at 296 K. The reaction has two possible branches; extraction of a methyl hydrogen or the carbonyl hydrogen. Measurements of the product yields indicate that abstraction of the carbonyl hydrogen is favored over the methyl hydrogen by 58±6% (k 1 a =8.1×10 −13 cm 3 mol −1 s −1 ) to 42±6% (k 1 b =5.9×10 −13 cm 3 mol −1 s −1 ) . The experimentally determined IR spectrum of CH 2 ClOC(O)H and CH 3 OC(O)Cl are presented and verified with high level ab initio calculations.

Ab initio molecular orbital theory, in combination with FTIR spectroscopy, has been used to determine a second-order rate constant for the hydrogen abstraction reaction involving bromoform and chlorine atom. The rate constant for the reaction is determined to be 2.7±0.2×10 −13 cm 3 molecule −1 s −1 at 298 K. Ab initio molecular orbital theory calculations at the QCISD(T)/6-311G(d,p)//MP2/6-31G(d) level of theory predict the barrier for the hydrogen abstraction reaction to be 1.6 kcal mol −1 . It has also been determined that, in the presence of oxygen, the reaction will lead to a one-to-one conversion of bromoform into carbonyl dibromide.

The compound 1,2,2,2-Tetrafluoroethyl Trifluoromethyl Ether, CF3OCHFCF3 (HFE-227), is currently being considered as a potential replacement for certain halocarbons, particularly for perfluorocarbons (PFCs), as a dry etching gas in the semiconductor industry. For this reason, it is important to determine the potential environmental effects resulting from the use and emissions of this compound. In this paper, the atmospheric lifetime, radiative forcing, and Global Warming Potentials (GWPs), an important measure of the potential effects of a gas on climate, are evaluated for this compound using our zonally averaged chemical transport and radiative transfer models of the atmosphere. To our knowledge, this is the first time this compound has been evaluated with such atmospheric models. In order to calculate the lifetime and radiative forcing, the rate constants and infrared cross sections of this compound were measured in laboratories at Illinois and Purdue, and results are reported here. The model-evaluated atmospheric lifetime is 11.3 years, mainly due to reaction with OH radicals. The model-evaluated instantaneous-clear-sky radiative forcing is 0.38 W m−2 ppbv−1, about 45% lower than previously estimated [Imasu et al., 1995]. However, the model-estimated cloudy-sky adjusted forcing, needed to calculated GWPs, is about 25% lower than the model-estimated instantaneous-clear-sky forcing. The GWPs are calculated to be 3400, 1200, and 370 for 20, 100, and 500 year time horizons, respectively.

Ab initio molecular orbital theory is coupled with laser flash photolysis experiments to study the UV spectrum and absorption cross section of the methyl formate radical. The vertical excitation energies for four of methyl formate radical's excited states are calculated at the MRCI level of theory. In the region between 220 and 340 nm, two electronic transitions are identified to explain the experimental UV spectrum.

We have examined CF3OCF = CF2 regarding its reactivity toward OH radical, its infrared spectroscopic properties, its atmospheric lifetime, and its radiative forcing. From these we then determined the Global Warming Potentials (GWPs) for CF3OCF = CF2. The examination is completed using a combination of discharge flow coupled with mass spectrometer and resonance fluorescence (DF/MS/RF), Fourier transform infrared (FTIR) spectroscopy, ab initio molecular orbital calculation, and atmospheric and radiative transfer modeling. Mass spectral evidence suggests that both HF and CF3OCFC(O)F are products from the reaction of CF3OCF = CF2 with OH. The Arrhenius expression for CF3OCF = CF2 + OH is determined to be k1 = (6.41±0.82)×10−11 exp[(−868±40)/T] cm3 molecule−1 s−1 in the temperature range of 253–348 K. The atmospheric lifetime of CF3OCF = CF2 is estimated to be less than 5 days due to the OH attack. The calculated vibrational frequencies using ab initio molecular orbital calculations are in good agreement with FTIR experimental observation for the CF3OCF = CF2 molecule. Both C-O and C-F stretching modes in the CF3OCF = CF2 contribute to prominent absorption in the atmospheric window region. The absolute adjusted radiative forcing at the tropopause due to an increase in the concentration of CF3OCF = CF2 by one part per billion by volume (ppbv) is calculated to be 0.041 W m−2 ppbv−1. The Global Warming Potential for CF3OCF = CF2 is evaluated to be 0.004 for 100-year time horizon.

Ab initio molecular orbital theory has been used to examine the kinetics and mechanism for the reaction of chlorine atoms with methyl formate. From the ab initio parameters, the room-temperature rate constant is calculated and found to be in reasonable agreement with the experimental determination. It is found that 90% of the reaction proceeds via abstraction of the carbonyl hydrogen from methyl formate by chlorine atoms, resulting in the formation of CH3OCO radical.

The reaction of the bromine oxide radical, BrO, with HBr has been examined with coupled-cluster methods. The HO+HCl reaction is also examined and is used to calibrate the results for the BrO+HBr reaction. The heat of reaction and activation energy barrier for BrO+HBr are calculated to be −9.3±4 and 3.6 kcal mol −1 , respectively.

The mechanism of the reaction of BrO + CH{sub 2}O has been examined using density functional and quadratic configuration interaction molecular orbital methods. The most favorable pathway is found to be the abstraction of hydrogen from CH{sub 2}O by BrO radicals. The activation energy barrier for the process is estimated as 219 {+-} 3 kcal mol{sup {minus}1}. Results from discharge flow/mass spectroscopy experiments support the finding that the major products of the reaction are HOBr and HCO radicals. The rate of the BrO + CH{sub 2}O reaction has been estimated by using transition state theory.

The formation of sulfuric acid (H(2)SO(4)), nitric acid (HNO(3)), acetic acid (CH(3)C(O)OH), and formic acid (HC(O))H) complexes with ammonia (NH(3)), amidogen radical (NH(2)), and imidogen radical (NH) was studied using natural bond orbital calculations. The equilibrium structures, binding energies, and harmonic frequencies were calculated for each acid-NH(x) complex using hybrid density functional (B3LYP) and second-order Møller-Plesset perturbation approximation methods with the 6-311++G(3df,3pd) basis set. The results presented here suggest that the effect of NH(2) on the formation of new condensation nuclei will be similar to that of NH(3), but to a lesser degree and confined primarily to complexes with H(2)SO(4) and HNO(3). The NH radical is not expected to play a significant role in the formation of new atmospheric condensation nuclei.

Rate coefficients k for the OH+Cl(2)O reaction are measured as a function of temperature (230-370 K) and pressure by using pulsed laser photolysis to produce OH radicals and laser-induced fluorescence to monitor their loss under pseudo-first-order conditions in OH. The reaction rate coefficient is found to be independent of pressure, within the precision of our measurements at 30-100 Torr (He) and 100 Torr (N(2)). The rate coefficients obtained at 100 Torr (He) showed a negative temperature dependence with a weak non-Arrhenius behavior. A room-temperature rate coefficient of k(1)(297 K)=(7.5±1.1)×10(-12) cm(3) molecule(-1) s(-1) is obtained, where the quoted uncertainties are 2σ and include estimated systematic errors. Theoretical methods are used to examine OH···OCl(2) and OH···ClOCl adduct formation and the potential-energy surfaces leading to the HOCl+ClO (1a) and Cl+HOOCl (1d) products in reaction (1) at the hybrid density functional UMPW1K/6-311++G(2df,p) level of theory. The OH···OCl(2) and OH···ClOCl adducts are found to have binding energies of about 0.2 kcal mol(-1). The reaction is calculated to proceed through weak pre-reactive complexes. Transition-state energies for channels (1a) and (1d) are calculated to be about 1.4 and about 3.3 kcal mol(-1) above the energy of the reactants. The results from the present study are compared with previously reported rate coefficients, and the interpretation of the possible non-Arrhenius behavior is discussed.

The U.S. Environmental Protection Agency is promoting the development and application of sampling methods for the semicontinuous determination of fine particulate matter (PM2.5, particles with an aerodynamic diameter2.5 microm) mass and chemical composition. Data obtained with these methods will significantly improve the understanding of the primary sources, chemical conversion processes, and meteorological atmospheric processes that lead to observed PM2.5 concentrations and will aid in the understanding of the etiology of PM2.5-related health effects. During January and February 2007, several semicontinuous particulate matter (PM) monitoring systems were compared at the Utah State Lindon Air Quality Sampling site. Semicontinuous monitors included instruments to measure total PM2.5 mass (filter dynamic measurement system [FDMS] tapered element oscillating microbalance [TEOM], GRIMM), nonvolatile PM2.5 mass (TEOM), sulfate and nitrate (two PM2.5 and one PM10 [PM with an aerodynamic diameter10 microm] ion-chromatographic-based samplers), and black carbon (aethalometer). PM10 semicontinuous mass measurements were made with GRIMM and TEOM instruments. These measurements were all made on a 1-hr average basis. Source apportionment analysis indicated that sources impacting the site were mainly urban sources and included mobile sources (gasoline and diesel) and residential burning of wood, with some elevated concentrations because of the effect of winter inversions. The FDMS TEOM and GRIMM instruments were in good agreement, but TEOM monitor measurements were low because of the presence of significant semi-volatile material. Semi-volatile mass was present dominantly in the PM2.5 mass.

The degradation rate and efficiency of digestion processes is typically measured by introducing a substrate or pollutant into a digester and then monitoring the effluents for the pollutant or substrate, a costly and slow process. A new method for rapid measurement of the rates and efficiencies of anaerobic degradation of pollutants and lignocellulose substrates from various pretreatments is described. The method uses micro-reactors (10–30 mL) containing a mixed culture of anaerobic bacteria obtained from a working anaerobic digester. The rate of degradation of pollutants and metabolic heat rate are measured in parallel sets of micro-reactors. Measurement of metabolic rate and pollutant degradation simultaneously is an effective means of rapidly examining pollutant degradation on a micro-scale. Calorimetric measurements alone allow rapid, relative evaluation of various substrate pretreatment methods.

The photolysis of chlorine peroxide (ClOOCl) is understood to be a key step in the destruction of polar stratospheric ozone. This study generated and purified ClOOCl in a novel fashion, which resulted in spectra with low impurity levels and high peak absorbances. The ClOOCl was generated by laser photolysis of Cl2 in the presence of ozone, or by photolysis of ozone in the presence of CF2Cl2. The product ClOOCl was collected, along with small amounts of impurities, in a trap at about -125 degrees C. Gas-phase ultraviolet spectra were recorded using a long path cell and spectrograph/diode array detector as the trap was slowly warmed. The spectrum of ClOOCl could be fit with two Gaussian-like expressions, corresponding to two different electronic transitions, having similar energies but different widths. The energies and band strengths of these two transitions compare favorably with previous ab initio calculations. The cross sections of ClOOCl at wavelengths longer than 300 nm are significantly lower than all previous measurements or estimates. These low cross sections in the photolytically active region of the solar spectrum result in a rate of photolysis of ClOOCl in the stratosphere that is much lower than currently recommended. For conditions representative of the polar vortex (solar zenith angle of 86 degrees, 20 km altitude, and O3 and temperature profiles measured in March 2000) calculated photolysis rates are a factor of 6 lower than the current JPL/NASA recommendation. This large discrepancy calls into question the completeness of present atmospheric models of polar ozone depletion.

Near-infrared spectroscopy was used to monitor HO_2 formed by pulsed laser photolysis of Cl_2−O_2−CH_3OH−N_2 mixtures. On the microsecond time scale, [HO_2] exhibited a time dependence consistent with a mechanism in which [HO_2] approached equilibrium via HO_2 + HO_3OH^M⇆_M HO_2·CH_3OH (3, −3). The equilibrium constant for reaction 3, Kp, was measured between 231 and 261 K at 50 and 100 Torr, leading to standard reaction enthalpy and entropy values (1 σ) of Δ_rH°_(246K) = −37.4 ± 4.8 kJ mol^(-1) and Δ_rS°_(246K) = −100 ± 19 J mol^(-1) K^(-1). The effective bimolecular rate constant, k_3, for formation of the HO_2·CH_3OH complex is 2.8^(+7.5)_(-2.0)·10^(-15)·exp[(1800 ± 500)/T] cm^3 molecule^(-1) s^(-1) at 100 Torr (1 σ). Ab initio calculations of the optimized structure and energetics of the HO_2·CH_3OH complex were performed at the CCSD(T)/6-311++G(3df,3pd)//MP2(full)/6-311++G(2df,2pd) level. The complex was found to have a strong hydrogen bond (D_e = 43.9 kJ mol^(-1)) with the hydrogen in HO_2 binding to the oxygen in CH_3OH. The calculated enthalpy for association is Δ_rH°_(245K) = −36.8 kJ mol^(-1). The potentials for the torsion about the O_2−H bond and for the hydrogen-bond stretch were computed and 1D vibrational levels determined. After explicitly accounting for these degrees of freedom, the calculated Third Law entropy of association is Δ_rS°_(245K) = −106 J mol^(-1) K^(-1). Both the calculated enthalpy and entropy of association are in reasonably good agreement with experiment. When combined with results from our previous study (Christensen et al. Geophys. Res. Lett. 2002, 29; doi:10.1029/2001GL014525), the rate coefficient for the reaction of HO_2 with the complex, HO_2 + HO_2·CH_3-OH, is determined to be (2.1 ± 0.7) × 10^(-11) cm^3 molecule^(-1) s^(-1). The results of the present work argue for a reinterpretation of the recent measurement of the HO_2 self-reaction rate constant by Stone and Rowley (Phys. Chem. Chem. Phys. 2005, 7, 2156). Significant complex concentrations are present at the high methanol concentrations used in that work and lead to a nonlinear methanol dependence of the apparent rate constant. This nonlinearity introduces substantial uncertainty in the extrapolation to zero methanol.