scholarly journals Uncertain Henry's Law Constants Compromise Equilibrium Partitioning Calculations of Atmospheric Oxidation Products

2017 ◽  
Author(s):  
Chen Wang ◽  
Tiange Yuan ◽  
Stephen A. Wood ◽  
Kai-Uwe Goss ◽  
Jingyi Li ◽  
...  
Keyword(s):  
Functional Groups ◽  
Organic Compounds ◽  
Estimation Method ◽  
Intramolecular Interactions ◽  
The Other ◽  
Oxidation Products ◽  
Chemical Mechanism ◽  
Phase Partitioning ◽  
Wide Range ◽  
Partitioning Coefficients

Abstract. Gas-particle partitioning governs the distribution, removal and transport of organic compounds in the atmosphere and the formation of secondary organic aerosol. The large variety of atmospheric species and their wide range of properties make predicting this partitioning equilibrium challenging. Here we expand on earlier work and predict gas-organic and gas-aqueous phase partitioning coefficients for 3414 atmospherically relevant molecules using COSMOtherm, SPARC and poly-parameter linear free energy relationships. The Master Chemical Mechanism generated the structures by oxidizing primary emitted volatile organic compounds. Predictions for gas-organic phase partitioning coefficients (KWIOM/G) by different methods are on average within one order of magnitude of each other, irrespective of the numbers of functional groups, except for predictions by COSMOtherm and SPARC for compounds with more than three functional groups, which have a slightly higher discrepancy. Discrepancies between predictions of gas-aqueous partitioning (KW/G) are much larger and increase with the number of functional groups in the molecule. In particular, COSMOtherm often predicts much lower KW/G for highly functionalized compounds than the other methods. While the quantum-chemistry based COSMOtherm accounts for the influence of intramolecular interactions on conformation, highly functionalized molecules likely fall outside of the applicability domain of the other techniques, which at least in part rely on empirical data for calibration. Further analysis suggests that atmospheric phase distribution calculations are sensitive to the partitioning coefficient estimation method, in particular to the estimated value of KW/G. The large uncertainty in KW/G predictions for highly functionalized organic compounds needs to be resolved to improve the quantitative treatment of SOA formation.

scholarly journals Uncertain Henry's law constants compromise equilibrium partitioning calculations of atmospheric oxidation products

2017 ◽  
Vol 17 (12) ◽  
pp. 7529-7540 ◽  
Author(s):  
Chen Wang ◽  
Tiange Yuan ◽  
Stephen A. Wood ◽  
Kai-Uwe Goss ◽  
Jingyi Li ◽  
...  
Keyword(s):  
Functional Groups ◽  
Organic Compounds ◽  
Phase Distribution ◽  
Estimation Method ◽  
The Other ◽  
Oxidation Products ◽  
Chemical Mechanism ◽  
Phase Partitioning ◽  
Wide Range ◽  
Partitioning Coefficients

Abstract. Gas–particle partitioning governs the distribution, removal, and transport of organic compounds in the atmosphere and the formation of secondary organic aerosol (SOA). The large variety of atmospheric species and their wide range of properties make predicting this partitioning equilibrium challenging. Here we expand on earlier work and predict gas–organic and gas–aqueous phase partitioning coefficients for 3414 atmospherically relevant molecules using COSMOtherm, SPARC Performs Automated Reasoning in Chemistry (SPARC), and poly-parameter linear free-energy relationships. The Master Chemical Mechanism generated the structures by oxidizing primary emitted volatile organic compounds. Predictions for gas–organic phase partitioning coefficients (KWIOM/G) by different methods are on average within 1 order of magnitude of each other, irrespective of the numbers of functional groups, except for predictions by COSMOtherm and SPARC for compounds with more than three functional groups, which have a slightly higher discrepancy. Discrepancies between predictions of gas–aqueous partitioning (KW/G) are much larger and increase with the number of functional groups in the molecule. In particular, COSMOtherm often predicts much lower KW/G for highly functionalized compounds than the other methods. While the quantum-chemistry-based COSMOtherm accounts for the influence of intra-molecular interactions on conformation, highly functionalized molecules likely fall outside of the applicability domain of the other techniques, which at least in part rely on empirical data for calibration. Further analysis suggests that atmospheric phase distribution calculations are sensitive to the partitioning coefficient estimation method, in particular to the estimated value of KW/G. The large uncertainty in KW/G predictions for highly functionalized organic compounds needs to be resolved to improve the quantitative treatment of SOA formation.

scholarly journals Coupling a gas chromatograph simultaneously to a flame ionization detector and chemical ionization mass spectrometer for isomer-resolved measurements of particle-phase organic compounds

2020 ◽  
Author(s):  
Chenyang Bi ◽  
Jordan E. Krechmer ◽  
Graham O. Frazier ◽  
Wen Xu ◽  
Andrew T. Lambe ◽  
...  
Keyword(s):  
Functional Groups ◽  
Organic Compounds ◽  
Mass Spectrometer ◽  
Chemical Ionization ◽  
Measurement Techniques ◽  
Oxidation Products ◽  
Ionization Mass ◽  
Particle Phase ◽  
Gas Chromatograph ◽  
New Instrument

Abstract. Atmospheric oxidation products of volatile organic compounds consist of thousands of unique chemicals that have distinctly different physical and chemical properties depending on their detailed structures and functional groups. Measurement techniques that can achieve molecular characterizations with details down to functional groups (i.e., isomer-resolved resolution) are consequently necessary to provide understandings of differences of fate and transport within isomers produced in the oxidation process. We demonstrate a new instrument coupling the thermal desorption aerosol gas chromatograph (TAG), which enables the separation of isomers, with the high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS), which has the capability of classifying unknown compounds by their molecular formulas, and the flame ion detector (FID), which provide a near-universal response to organic compounds. The TAG-CIMS/FID is used to provide isomer-resolved measurements of samples from liquid standard injections and particle-phase organics generated in oxidation flow reactors. By coupling a TAG to a CIMS, the CIMS is enhanced with an additional dimension of information (resolution of individual molecules) at the cost of time resolution (i.e., one sample per hour instead of per minute). We found that isomers are prevalent in sample matrix with an average number of three to five isomers per formula depending on the precursors in the oxidation experiments. Additionally, a multi-reagent ionization mode is investigated in which both zero air and iodide are introduced as reagent ions, to examine the feasibility of extending the use of an individual CIMS to a broader range of analytes with still selective reagent ions. While this approach reduces iodide-adduct ions by a factor of two, [M−H]− and [M+O2]− ions produced from lower-polarity compounds increase by a factor of five to ten, improving their detection by CIMS. The method expands the range of detected chemical species by using two chemical ionization reagents simultaneously, enabled by the pre-separation of analyte molecules before ionization.

scholarly journals Explicit modelling of SOA formation from α-pinene photooxidation: sensitivity to vapour pressure estimation

2011 ◽  
Vol 11 (3) ◽  
pp. 10121-10158 ◽  
Author(s):  
R. Valorso ◽  
B. Aumont ◽  
M. Camredon ◽  
T. Raventos-Duran ◽  
C. Mouchel-Vallon ◽  
...  
Keyword(s):  
Organic Compounds ◽  
Vapour Pressure ◽  
Estimation Method ◽  
Organic Aerosol ◽  
Reaction Scheme ◽  
Oxidation Products ◽  
Organic Species ◽  
Structure Activity ◽  
Volatile Organic ◽  
Kinetics Of

Abstract. The sensitivity of the formation of secondary organic aerosol (SOA) to the estimated vapour pressures of the condensable oxidation products is explored. A highly detailed reaction scheme was generated for α-pinene photooxidation using the Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A). Vapour pressures (Pvap) were estimated with three commonly used structure activity relationships. The values of Pvap were compared for the set of secondary species generated by GECKO-A to describe α-pinene oxidation. Discrepancies in the predicted vapour pressures were found to increase with the number of functional groups borne by the species. For semi-volatile organic compounds (i.e. organic species of interest for SOA formation), differences in the predicted Pvap range between a factor of 5 to 200 in average. The simulated SOA concentrations were compared to SOA observations in the Caltech chamber during three experiments performed under a range of NOx conditions. While the model captures the qualitative features of SOA formation for the chamber experiments, SOA concentrations are systematically overestimated. For the conditions simulated, the modelled SOA speciation appears to be rather insensitive to the Pvap estimation method.

Estimation of Properties of Organic Compounds

2001 ◽  
Author(s):  
L. K. Doraiswamy
Keyword(s):  
Organic Compounds ◽  
Process Development ◽  
Ideal Gas ◽  
The Other ◽  
Ideal Gas Law ◽  
Wide Range ◽  
Law Of Corresponding States ◽  
Pvt Behavior ◽  
Reduced Temperature ◽  
Simple Ideal

A primary requirement of any reactor design or process development computation is knowledge of the major properties of the compounds involved. Although most of these can be obtained from the literature, there is still a need to estimate them from correlations. The main difficulty is the large number of correlations proposed for a given property and the need to select the best from among them. No single correlation works with equally high precision under all conditions. On the other hand, correlations that can be used with acceptable levels of precision over a wide range of conditions are also available for a number of properties. The slight sacrifice of accuracy is often more than compensated for by the ease and generality of application of these methods. Our emphasis here will be on such correlations. For a detailed treatment, reference should be made to books devoted exclusively to properties estimation. The book by Reid, Prausnitz, and Poling (1987), along with its earlier versions by Reid and Sherwood (1958, 1966) and Reid, Prausnitz, and Sherwood (1977), and the works of Janz (1958), Hansch and Leo (1979), and Lyman, Reehl, and Rosenblatt (1982) are noteworthy. The following methods selected for a few properties are based in part on the recommendations contained in these treatises. The two most important bases for formulating correlations for estimating the properties of organic compounds (indeed of any compound) are the law of corresponding states (LCS), and the method of group contributions (GC). LCS is based on the concept that all substances exhibit identical properties under conditions equally removed from their critical states. The “equally removed” state for any property is usually expressed as the ratio of its value at that state to the value at the critical state and is referred to as the reduced property. Thus Tr — T/TC, Pr = P/PC, Vr = V/Vc and ηr = η/ ηc are the reduced temperature, pressure, volume, and viscosity, respectively. If the simple ideal gas law PV/RgT — Z, where Z is the compressibility, can be recast in terms of reduced properties as PrVt/RgTr = Z/ZC, then the PVT behavior of all fluids can be represented as Pr versus Tr plots for different values of Zr.

scholarly journals EVAPORATION: a new vapor pressure estimation method for organic molecules including non-additivity and intramolecular interactions

2011 ◽  
Vol 11 (4) ◽  
pp. 13229-13278
Author(s):  
S. Compernolle ◽  
K. Ceulemans ◽  
J.-F. Müller
Keyword(s):  
Molecular Structure ◽  
Vapor Pressure ◽  
Functional Groups ◽  
Vapour Pressure ◽  
Simple Formula ◽  
Organic Molecules ◽  
Intramolecular Interaction ◽  
Estimation Method ◽  
Organic Aerosol ◽  
Intramolecular Interactions

Abstract. We present EVAPORATION (Estimation of VApour Pressure of ORganics, Accounting for Temperature, Intramolecular, and Non-additivity effects), a method to predict vapour pressure p0 of organic molecules needing only molecular structure as input. The method is applicable to zero-, mono- and polyfunctional molecules. A simple formula to describe log10p0(T) is employed, that takes into account both a wide temperature dependence and the non-additivity of functional groups. In order to match the recent data on functionalised diacids an empirical modification to the method was introduced. Contributions due to carbon skeleton, functional groups, and intramolecular interaction between groups are included. Molecules typically originating from oxidation of biogenic molecules are within the scope of this method: carbonyls, alcohols, ethers, esters, nitrates, acids, peroxides, hydroperoxides, peroxy acyl nitrates and peracids. Therefore the method is especially suited to describe compounds forming secondary organic aerosol (SOA).

scholarly journals Modelling the formation and composition of secondary organic aerosol from α- and β-pinene ozonolysis using MCM v3

2004 ◽  
Vol 4 (3) ◽  
pp. 2905-2948 ◽  
Author(s):  
M. E. Jenkin
Keyword(s):  
Secondary Organic Aerosol ◽  
Experimental Studies ◽  
Organic Aerosol ◽  
Chemical Mechanism ◽  
Oh Radicals ◽  
Product Distributions ◽  
Wide Range ◽  
Partitioning Coefficients ◽  
Detailed Composition ◽  
Multifunctional Products

Abstract. The formation and detailed composition of secondary organic aerosol (SOA) from the gas phase ozonolysis of α- and β-pinene has been simulated using the Master Chemical Mechanism version 3 (MCM v3), coupled with a representation of gas-to-aerosol transfer of semivolatile and involatile oxygenated products. A kinetics representation, based on equilibrium absorptive partitioning of ca. 200 semivolatile products, was found to provide an acceptable description of the final mass concentrations observed in a number of reported laboratory and chamber experiments, provided partitioning coefficients were increased by about two orders of magnitude over those defined on the basis of estimated vapour pressures. This adjustment is believed to be due, at least partially, to the effect of condensed phase association reactions of the partitioning products. Even with this adjustment, the simulated initial formation of SOA was delayed relative to that observed, implying the requirement for the formation of species of much lower volatility to initiate SOA formation. The inclusion of a simplified representation of the formation and gas-to-aerosol transfer of involatile dimers of 22 bi- and multifunctional carboxylic acids (in addition to the absorptive partitioning mechanism) allowed a much improved description of SOA formation for a wide range of conditions. The simulated SOA composition recreates certain features of the product distributions observed in a number of experimental studies, but implies an important role for multifunctional products containing hydroperoxy groups (i.e. hydroperoxides). This is particularly the case for experiments in which 2-butanol is used to scavenge OH radicals, because [HO2]/[RO2] ratios are elevated in such systems. The optimized mechanism is used to calculate SOA yields from α- and β-pinene ozonolysis in the presence and absence of OH scavengers, and as a function of temperature.

Mechanisms of Photodecomposition of the Sunlight-Absorbing Oxygenates

2011 ◽  
Author(s):  
Jack Calvert ◽  
Abdelwahid Mellouki ◽  
John Orlando ◽  
Michael Pilling ◽  
Timothy Wallington
Keyword(s):  
Organic Compounds ◽  
Light Absorption ◽  
The Other ◽  
Oxidation Products ◽  
Hydrocarbon Oxidation ◽  
Absorption Data ◽  
Absorption Bands ◽  
Chemical Changes ◽  
Atmospheric Processes ◽  
Oxygenated Products

In this chapter we consider the chemical changes induced by absorption of sunlight by oxygenated organic compounds. In contrast to the hydrocarbons, sunlight absorption by the oxygenated products of hydrocarbon oxidation shows a shift in absorption to the longer wavelengths such that their photodecompositions can become important atmospheric processes. This is illustrated in the absorption data given for methane and its oxidation products in figure IX-A-1. As a H3C—H bond in methane is replaced with a H3C—OH bond (alcohols), H3C—OCH3 bond (ethers), or H3C—O2H bond (hydroperoxides), light absorption involving excitation of nonbonding O-atom electrons to an antibonding sigma orbital (n → σ* transitions) becomes possible. These “forbidden” absorptions are smaller than the allowed σ → σ*transitions in the CH4 and the other alkanes, but the absorption bands are shifted to longer wavelengths progressing from CH4 to CH3OH, CH3OCH3, and CH3OOH as less energy is required to excite the nonbonding electron to the σ* orbital.

scholarly journals Simulating the detailed chemical composition of secondary organic aerosol formed on a regional scale during the TORCH 2003 campaign in the southern UK

2006 ◽  
Vol 6 (2) ◽  
pp. 419-431 ◽  
Author(s):  
D. Johnson ◽  
S. R. Utembe ◽  
M. E. Jenkin
Keyword(s):  
Chemical Composition ◽  
Secondary Organic Aerosol ◽  
Regional Scale ◽  
Equilibrium Phase ◽  
Organic Aerosol ◽  
Oxidation Products ◽  
Chemical Mechanism ◽  
Phase Partitioning ◽  
Biogenic Voc ◽  
Detailed Chemical

Abstract. Following on from the companion study (Johnson et al., 2006), a photochemical trajectory model (PTM) has been used to simulate the chemical composition of organic aerosol for selected events during the 2003 TORCH (Tropospheric Organic Chemistry Experiment) field campaign. The PTM incorporates the speciated emissions of 124 non-methane anthropogenic volatile organic compounds (VOC) and three representative biogenic VOC, a highly-detailed representation of the atmospheric degradation of these VOC, the emission of primary organic aerosol (POA) material and the formation of secondary organic aerosol (SOA) material. SOA formation was represented by the transfer of semi- and non-volatile oxidation products from the gas-phase to a condensed organic aerosol-phase, according to estimated thermodynamic equilibrium phase-partitioning characteristics for around 2000 reaction products. After significantly scaling all phase-partitioning coefficients, and assuming a persistent background organic aerosol (both required in order to match the observed organic aerosol loadings), the detailed chemical composition of the simulated SOA has been investigated in terms of intermediate oxygenated species in the Master Chemical Mechanism, version 3.1 (MCM v3.1). For the various case studies considered, 90% of the simulated SOA mass comprises between ca. 70 and 100 multifunctional oxygenated species derived, in varying amounts, from the photooxidation of VOC of anthropogenic and biogenic origin. The anthropogenic contribution is dominated by aromatic hydrocarbons and the biogenic contribution by α- and β-pinene (which also constitute surrogates for other emitted monoterpene species). Sensitivity in the simulated mass of SOA to changes in the emission rates of anthropogenic and biogenic VOC has also been investigated for 11 case study events, and the results have been compared to the detailed chemical composition data. The role of accretion chemistry in SOA formation, and its implications for the results of the present investigation, is discussed.

scholarly journals A thermodynamic model of mixed organic-inorganic aerosols to predict activity coefficients

2008 ◽  
Vol 8 (2) ◽  
pp. 6069-6151 ◽  
Author(s):  
A. Zuend ◽  
C. Marcolli ◽  
B. P. Luo ◽  
Th. Peter
Keyword(s):  
Functional Groups ◽  
Organic Compounds ◽  
Activity Coefficients ◽  
Thermodynamic Model ◽  
Liquid Mixtures ◽  
Model Framework ◽  
Alcohol Water ◽  
Wide Range ◽  
Water Salt ◽  
Liquid Phase Separations

Abstract. Tropospheric aerosols contain mixtures of inorganic salts, acids, water, and a large variety of organic compounds. Interactions between these substances in liquid mixtures lead to discrepancies from ideal thermodynamic behaviour. By means of activity coefficients, non-ideal behaviour can be taken into account. We present here a thermodynamic model named AIOMFAC (Aerosol Inorganic–Organic Mixtures Functional groups Activity Coefficients) that is able to calculate activity coefficients covering inorganic, organic, and organic–inorganic interactions in aqueous solutions over a wide concentration range. This model is based on the activity coefficient model LIFAC by Yan et al. (1999) that we modified and reparametrised to better describe atmospherically relevant conditions and mixture compositions. Focusing on atmospheric applications we considered H+, Li+, Na+, K+, NH4+, Mg2+, Ca2+, Cl−, Br−, NO3−, HSO4−, and SO42− as cations and anions and a wide range of alcohols/polyols composed of the functional groups CHn and OH as organic compounds. With AIOMFAC, the activities of the components within an aqueous electrolyte solution are well represented up to high ionic strength. Most notably, a semi-empirical middle-range parametrisation of direct organic–inorganic interactions in alcohol + water + salt solutions strongly improves the agreement between experimental and modelled activity coefficients. At room temperature, this novel thermodynamic model offers the possibility to compute equilibrium relative humidities, gas/particle partitioning and liquid–liquid phase separations with high accuracy. In further studies, other organic functional groups will be introduced. The model framework is not restricted to specific ions or organic compounds and is therefore also applicable for other research topics.

scholarly journals Explicit modelling of SOA formation from α-pinene photooxidation: sensitivity to vapour pressure estimation

2011 ◽  
Vol 11 (14) ◽  
pp. 6895-6910 ◽  
Author(s):  
R. Valorso ◽  
B. Aumont ◽  
M. Camredon ◽  
T. Raventos-Duran ◽  
C. Mouchel-Vallon ◽  
...  
Keyword(s):  
Organic Compounds ◽  
Vapour Pressure ◽  
Estimation Method ◽  
Organic Aerosol ◽  
Reaction Scheme ◽  
Oxidation Products ◽  
Organic Species ◽  
Structure Activity ◽  
Volatile Organic ◽  
Kinetics Of

Abstract. The sensitivity of the formation of secondary organic aerosol (SOA) to the estimated vapour pressures of the condensable oxidation products is explored. A highly detailed reaction scheme was generated for α-pinene photooxidation using the Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A). Vapour pressures (Pvap) were estimated with three commonly used structure activity relationships. The values of Pvap were compared for the set of secondary species generated by GECKO-A to describe α-pinene oxidation. Discrepancies in the predicted vapour pressures were found to increase with the number of functional groups borne by the species. For semi-volatile organic compounds (i.e. organic species of interest for SOA formation), differences in the predicted Pvap range between a factor of 5 to 200 on average. The simulated SOA concentrations were compared to SOA observations in the Caltech chamber during three experiments performed under a range of NOx conditions. While the model captures the qualitative features of SOA formation for the chamber experiments, SOA concentrations are systematically overestimated. For the conditions simulated, the modelled SOA speciation appears to be rather insensitive to the Pvap estimation method.

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