Non-volatile Species Research Articles

Hazardous Waste Vitrification by Plasma Gasification Process

Hazardous Wastes Control is one of the major problems of waste management companies and governmentand environment and disposal of such hazardous wastes is critical and problematic. Current method of hazardous waste disposal,which include mass burn or incineration, and landfilling create new problems to the environment. Vitrification of such wastes by thermal plasma gasification process appears to be a solution to hazardous waste disposal that does not create further problems to the environment. The energy generated by plasma arcs has been recently applied to hazardous waste vitrification. The technology involves subjecting waste material to high temperatures with the purpose of immobilizing nonvolatile chemical species into a nonleachable matrix. Plasma arc gasification and vitrification processes are well known for special waste disposal requirements. This paper presents the high tech plasma gasification processas an efficient technological tool for hazardous waste destruction, such as hospital wastes, nuclear wastes, pyrotechnic smoke assemblies, thermal batteries, and other military wastes. Results show that thermal plasma gasification process is effective in hazardous waste vitrification.

Mixing State of Size-Selected Submicrometer Particles in the Arctic in May and September 2012

Aerosols have been associated with large uncertainties in estimates of the radiation budget and cloud formation processes in the Arctic. This paper reports the results of a study of in situ measurements of hygroscopicity, fraction of volatile species, mixing state, and off-line morphological and elemental analysis of Aitken and accumulation mode particles in the Arctic (Ny-Ålesund, Svalbard) in May and September 2012. The accumulation mode particles were more abundant in May than in September. This difference was due to more air mass flow from lower latitude continental areas, weaker vertical mixing, and less wet scavenging in May than in September, which may have led to a higher amount of long-range transport aerosols entering the Arctic in the spring. The Aitken mode particles observed intermittently in May were produced by nucleation, absent significant external mixing, whereas the accumulation mode particles displayed significant external mixing. The occurrence of an external mixing state was observed more often in May than in September and more often in accumulation mode particles than in Aitken mode particles, and it was associated more with continental air masses (Siberian) than with other air masses. The external mixing of the accumulation mode particles in May may have been caused by multiple sources (i.e., long-range transport aerosols with aging and marine aerosols). These groups of externally mixed particles were subdivided into different mixing structures (internal mixtures of predominantly sulfates and volatile organics without nonvolatile species and internal mixtures of sulfates and nonvolatile components, such as sea salts, minerals, and soot). The variations in the mixing states and chemical species of the Arctic aerosols in terms of their sizes, air masses, and seasons suggest that the continuous size-dependent measurements observed in this study are useful for obtaining better estimates of the effects of these aerosols on climate change.

Modeling differential scanning calorimetry of thermally degrading thermoplastics

Differential scanning calorimetry (DSC) of thermally degrading thermoplastics is modeled using a discrete population balance equation (PBE). The PBE allows for species mole change due to pyrolysis and bubbling mass loss. Efficient solution is achieved by lumping non-volatile species into a single, notional “polymer” species. Thermodynamic properties are calculated by group additivity techniques, and empirical corrections are made to account for the changes in specific heat capacity and enthalpy upon mixing. Simulation results for high-density polyethylene (HDPE) are compared to literature data for DSC at heating rates of 5, 10, and 20K/min. The model predicts peak energy absorption rates to within 4% at the lowest heating rate. The heat of decomposition was found to be within 17% of literature values at all three heating rates. The predicted pyrolysis gas species distribution agrees well with literature gas chromatography–mass spectrometry (GC–MS) data.

From Chemical Solutions to Inorganic Nanostructured Materials: A Journey into Evaporation-Driven Processes

We present the conventional and emerging methods of preparation of nanostructured materials from chemical solution evaporation where precursors, reactants, and potential structuring agents are homogeneously dispersed or dissolved in a volatile solvent. The liquid is shaped as dictated by the selected process and undergoes evaporation that concentrates the nonvolatile species triggering various chemical phenomena such as reaction, self-assembly, phase separation, nucleation growth, aggregation, etc. While the composition of the final material depends on the initial solution stoichiometry, the morphology is governed by the process and the internal structure is adjusted by the kinetic and thermodynamic aspects of the coupled process. Because many processes involving the later approach exist, we decided to describe some of the more important processes, in terms of applicability and some of the more emerging processes, in terms of added value. More precisely, thin films, two-dimensional (2D) nano-in-micro patterns, hierarchical structures, and powders presented here were prepared by combining the solution evaporation with dip coating, microfabrication and nanofabrication, infiltration–replication (especially of butterfly wings), and, finally, spray drying, respectively. The efficiency, throughput, compatibility, and limitation of each process and method are discussed, together with related priority developments to be made in the future.

Profiling Hoodia Extracts by HPLC with Charged Aerosol Detection and Electrochemical Array Detection and Pattern Recognition

Hoodigosides are oxypregnane steroidal glycosides abundant in Hoodia gordonii and related plants native to the deserts of southwestern Africa. These plants, used traditionally to ease hunger, enjoy wide use today in dietary supplements purported to suppress appetite and aid in weight loss. Presented are two approaches to profile Hoodia related products. First, Hoodia extracts were analyzed by HPLC with charged aerosol detection. Eight hoodigosides isolated from dried plant material were separated within 15 min on a solid core enhanced C8 analytical column. With low-nanogram sensitivity, the charged aerosol detector responds uniformly to all non-volatile species including the target analytes, degradation products and impurities that may not possess a chromophore. Second, Hoodia extracts were analyzed by gradient HPLC with an online electrochemical array detector that responds to redox active compounds such as polyphenols. Each of the sixteen sensors in the electrochemical array detects analytes at a unique potential to yield picogram on-column sensitivity for diverse compounds that vary widely in redox properties. The chromatograms resulting from this voltammetric approach often clearly resolve co-eluting compounds. These two techniques provide complementary data that were used to quantify known compounds. The complex patterns of both known and unknown compounds revealed by the detectors were also interrogated by pattern recognition software to support inferences on product quality, authenticity, adulteration, or origin. Limits of detection, linear and dynamic range, precision, and pattern recognition results are compared for the two approaches.

Equilibrium Approach for CO2 and H2S Absorption with Aqueous Solutions of Alkanolamines: Theory and Parameter Estimation

Acid gas removal from gas streams is mainly executed industrially via aqueous alkanolamines absorption, whose modeling often involves ionic nonequilibrium chemical reactions and mass/heat interfacial transfers. This demands high computational efforts and often nonavailable physical parameters. Also, the role of ions, created by weak dissociations, is not well understood, and despite the high pressures, concentrations, and loadings, idealities are often recruited, such as ideal laws for gas and mass action. In this work, these issues are circumvented by prescribing only molecular species incorporated into a chemical theory equilibrium framework using full thermodynamics via cubic equations of state. Nonvolatile molecular Complex species are formed via equilibrium reactions involving acid gas, water, and alkanolamines (AGWA) systems. The approach is calibrated with large sets of AGWA data, partial pressures, and loadings, by searching equilibrium constants via maximum likelihood nonlinear implicit parameter estimation. These constants are used to address ideal gas properties of Complex species, which are necessary to model energy effects in AGWA separations.

Mixing State of Size-Selected Submicrometer Particles During Photochemical and Combustion Events Measured with the Tandem System

A tandem differential mobility analyzer (TDMA) was applied to determine the mixing state of size-resolved submicrometer particles, in an urban area of Gwangju in Korea, when enhanced concentrations of particles were observed (e.g., photochemical and combustion events). The existence of a nonvolatile core was identified after removing volatile species with increasing temperature up to ∼250°C. Data showed that in the combustion event, the accumulation mode particles (137–139 nm) increased significantly and they had a nonvolatile core coated with volatile species, while in the photochemical event, the nucleation mode (15–30 nm) particles enhanced and there was no such nonvolatile core (i.e., they were completely evaporated below 250°C). When hygroscopic growth factor (HGF) of the core particles was measured in the combustion event, their values were close to one, suggesting that they consist of nonvolatile and nonhygroscopic species like black carbon. In the photochemical event, the nucleation mode particles were completely evaporated at 250°C and had some volatile fractions at 100°C, unlike pure ammonium sulfate, and had C and S elements in their TEM/EDS data, suggesting that they have an internal mixture of sulfate and organics. Also, the HGF of the remaining particles after removing volatile species at 150°C increased, but not as much as expected for the case of complete evaporation of volatile species at this temperature. Data for evaporative behaviors of laboratory-generated aerosols (i.e., ammonium sulfate and succinic acid) suggest that evaporation of volatile species in a well-mixed mixture was delayed compared to those existing as single species.Copyright 2013 American Association for Aerosol Research

A Multiple-Scale Analysis of Evaporation Induced Marangoni Convection

This paper considers the stability of thin liquid layers of binary mixtures of a volatile (solvent) species and a nonvolatile (polymer) species. Evaporation leads to a depletion of the solvent near the liquid surface. If surface tension increases for lower solvent concentrations, sufficiently strong compositional gradients can lead to Bénard--Marangoni-type convection that is similar to the kind which is observed in films that are heated from below. The onset of the instability is investigated by a linear stability analysis. Due to evaporation, the base state is time dependent, thus leading to a nonautonomous linearized system which impedes the use of normal modes. However, the time scale for the solvent loss due to evaporation is typically long compared to the diffusive time scale, so a systematic multiple scales expansion can be sought for a finite-dimensional approximation of the linearized problem. This is determined to leading and to next order. The corrections indicate that the validity of the expansion does not depend on the magnitude of the individual eigenvalues of the linear operator, but it requires these eigenvalues to be well separated. The approximations are applied to analyze experiments by Bassou and Rharbi with polystyrene/toluene mixtures [Langmuir, 25 (2009), pp. 624--632].

Efficient surface formation route of interstellar hydroxylamine through NO hydrogenation. I. The submonolayer regime on interstellar relevant substrates

Dust grains in the interstellar medium are known to serve as the first chemical laboratory where the rich inventory of interstellar molecules are synthesized. Here we present a study of the formation of hydroxylamine--NH(2)OH--via the non-energetic route NO + H (D) on crystalline H(2)O and amorphous silicate under conditions relevant to interstellar dense clouds. Formation of nitrous oxide (N(2)O) and water (H(2)O, D(2)O) is also observed and the reaction network is discussed. Hydroxylamine and water results are detected in temperature-programmed desorption (TPD) experiments, while N(2)O is detected by both reflection-absorption IR spectroscopy and TPD techniques. The solid state NO + H reaction channel proves to be a very efficient pathway to NH(2)OH formation in space and may be a potential starting point for prebiotic species in dark interstellar clouds. The present findings are an important step forward in understanding the inclusion of interstellar nitrogen into a non-volatile aminated species since NH(2)OH provides a solid state nitrogen reservoir along the whole evolutionary process of interstellar ices from dark clouds to planetary systems.

Enceladus: A hypothesis for bringing both heat and chemicals to the surface

The eruptive plumes and large heat flow (∼15GW) observed by Cassini in the South Polar Region of Enceladus may be expressions of hydrothermal activity inside Enceladus. We hypothesize that a subsurface ocean is the heat reservoir for thermal anomalies on the surface and the source of heat and chemicals necessary for the plumes. The ocean is believed to contain dissolved gases, mostly CO2 and is found to be relatively warm (∼0°C). Regular tidal forces open cracks in the icy crust above the ocean. Ocean water fills these fissures. There, the conditions are met for the upward movement of water and the dissolved gases to exsolve and form bubbles, lowering the bulk density of the water column and making the pressure at its bottom less than that at the top of the ocean. This pressure difference drives ocean water into and up the conduits toward the surface. This transportation mechanism supports the thermal anomalies and delivers heat and chemicals to the chambers from which the plumes erupt. Water enters these chambers and there its bubbles pop and loft an aerosol mist into the ullage. The exiting plume gas entrains some of these small droplets. Thus, nonvolatile chemical species in ocean water can be present in the plume particles. A CO2 equivalent-gas molar fraction of ∼4×10−4 for the ocean is sufficient to support the circulation. A source of heat is needed to keep the ocean warm at ∼0°C (about two degrees above its freezing point). The source of heat is unknown, but our hypothesis is not dependent on any particular mechanism for producing the heat.

Formation and stability of bulk carbonic acid (H2CO3) by protonation of tropospheric calcite.

Organic acids play an important role in the acidification of our atmosphere. These weak acids can contribute up to 60 % of the free airborne acidity. By far the most abundant organic acids are the C1 and C2 monocarboxylic acids, formic acid (HCOOH) and acetic acid (CH3COOH), which show mixing ratios in the gas phase ranging up to 20 ppb over land1,2 and down to 0.2 ppb in the remote oceanic boundary layer or troposphere.3,4 These acids are partitioned between the gas phase and the particulate phase, where roughly one half to two thirds can be found in particulate matter (PM2.5).2 The most important removal mechanism is dry deposition, which accounts for more than 90 % of the total organic acid deposition budget. The remaining fraction is removed by rain as particulate-phase acids, whereas removal by chemical reactions is negligible.1,5 In addition to the two most important organic acids, C3–C10 aliphatic monocarboxylic acids1 and C2–C11 aliphatic dicarboxylic acids1,2,6–11 as well as aromatic carboxylic acids1 have also been observed in air. The water-soluble fraction of organic carbon can on average consist of 35 % mono- and dicarboxylic acids.12 While the C2-dicarboxylic acid, oxalic acid (COOH)2, is commonly observed in all field studies, the C1-dicarboxylic acid, carbonic acid (H2CO3), has barely received any attention, mainly because it is thought that it immediately decomposes to water and carbon dioxide. However, it has previously been shown that gaseous, water-free carbonic acid is surprisingly stable,13 that amorphous and crystalline solids of pure carbonic acid can be produced and stored without decomposition at temperatures up to 230 K even in the presence of water14 and that this solid can be sublimed at, for example, 220 K and recondensed in vacuo at surfaces of lower temperature.15

Insight into the Interactions That Control the Phase Behaviour of New Aqueous Biphasic Systems Composed of Polyethylene Glycol Polymers and Ionic Liquids

New polyethylene glycol (PEG)/ionic liquid aqueous biphasic systems (ABS) are presented. Distinct pairs of PEG polymers and ionic liquids can induce phase separation in aqueous media when dissolved at appropriate concentrations. Phase diagrams have been determined for a large array of systems at 298, 308 and 323 K. A comparison of the binodal curves allowed the analysis of the tunable structural features of the ionic liquid (i.e., anionic nature, cationic core, cationic alkyl side chain length and functionalisation, and number of alkyl substituents in the cation) and the influence of the molecular weight of the PEG polymer on the ability of these solutes to induce an ABS. It was observed that contrary to typical ABS based on ionic liquids and inorganic salts, in which the phase behaviour is dominated by the formation of the hydration complexes of the ions, the interactions between the PEG polymers and ionic liquids control the phase demixing in the polymer-type ABS studied herein. It is shown that both the ionic liquids and PEG polymers can act as the salting-out species; that is, it is an occurrence that is dependent on the structural features of the ionic liquid. For the first time, PEG/ionic liquid ABS are reported and insight into the major interactions that govern the polymer/ionic liquid phase behaviour in aqueous media are provided. The use of two different nonvolatile and tunable species (i.e., ionic liquids and PEG polymers) to form ABS allows the polarities of the phases to be tailored. Hence, the development of environmentally friendly separation processes that make use of these novel systems is envisaged.

Modeling anthropogenically controlled secondary organic aerosols in a megacity: a simplified framework for global and climate models

Abstract. A simplified parameterization for secondary organic aerosol (SOA) formation in polluted air and biomass burning smoke is tested and optimized in this work, towards the goal of a computationally inexpensive method to calculate pollution and biomass burning SOA mass and hygroscopicity in global and climate models. A regional chemistry-transport model is used as the testbed for the parameterization, which is compared against observations from the Mexico City metropolitan area during the MILAGRO 2006 field experiment. The empirical parameterization is based on the observed proportionality of SOA concentrations to excess CO and photochemical age of the airmass. The approach consists in emitting an organic gas as lumped SOA precursor surrogate proportional to anthropogenic or biomass burning CO emissions according to the observed ratio between SOA and CO in aged air, and reacting this surrogate with OH into a single non-volatile species that condenses to form SOA. An emission factor of 0.08 g of the lumped SOA precursor per g of CO and a rate constant with OH of 1.25 × 10−11 cm3 molecule−1 s−1 reproduce the observed average SOA mass within 30 % in the urban area and downwind. When a 2.5 times slower rate is used (5 × 10−12 cm3 molecule−1 s−1) the predicted SOA amount and temporal evolution is nearly identical to the results obtained with SOA formation from semi-volatile and intermediate volatility primary organic vapors according to the Robinson et al. (2007) formulation. Our simplified method has the advantage of being much less computationally expensive than Robinson-type methods, and can be used in regions where the emissions of SOA precursors are not yet available. As the aged SOA/ΔCO ratios are rather consistent globally for anthropogenic pollution, this parameterization could be reasonably tested in and applied to other regions. The evolution of oxygen-to-carbon ratio was also empirically modeled and the predicted levels were found to be in reasonable agreement with observations. The potential enhancement of biogenic SOA by anthropogenic pollution, which has been suggested to play a major role in global SOA formation, is also tested using two simple parameterizations. Our results suggest that the pollution enhancement of biogenic SOA could provide additional SOA, but does not however explain the concentrations or the spatial and temporal variations of measured SOA mass in the vicinity of Mexico City, which appears to be controlled by anthropogenic sources. The contribution of the biomass burning to the predicted SOA is less than 10% during the studied period.

Towards understanding reactive adsorption of small molecule toxic gases on carbonaceous materials

Reactive adsorption is a separation process based on physical adsorption of molecules, which is followed by their chemical transformations on the surface. This process is especially important for the removal of toxic industrial compounds (TICs) from air. At ambient conditions their adsorption is very weak and such factors as the presence of humidity have to be taken into account. This paper presents our approach leading to the design of efficient TICs adsorbents. In these materials the pores should be small enough to attract adsorbate molecules but sufficiently big to accommodate water or functional groups which participate in surface reactions. In these specific nanoreactors toxic species are either transformed to nontoxic and removed from the system or they are strongly retained on the surface via chemical bonds or as nonvolatile species. Surface chemistry is very important for these transformations. To start designing new separation media the physical properties of molecules and their chemical reactivity should be of paramount importance. After a separation performance test the battery of analytical methods has to be employed to characterize the surface of materials before and after reactive adsorption. The results obtained are then analyzed and the mechanism of adsorption is derived with the indication of surface features, which play a critical role in a particular separation process.

Growth of Graphene from Food, Insects, and Waste

In its monolayer form, graphene is a one-atom-thick two-dimensional material with excellent electrical, mechanical, and thermal properties. Large-scale production of high-quality graphene is attracting an increasing amount of attention. Chemical vapor and solid deposition methods have been developed to grow graphene from organic gases or solid carbon sources. Most of the carbon sources used were purified chemicals that could be expensive for mass production. In this work, we have developed a less expensive approach using six easily obtained, low or negatively valued raw carbon-containing materials used without prepurification (cookies, chocolate, grass, plastics, roaches, and dog feces) to grow graphene directly on the backside of a Cu foil at 1050 °C under H(2)/Ar flow. The nonvolatile pyrolyzed species were easily removed by etching away the frontside of the Cu. Analysis by Raman spectroscopy, X-ray photoelectron spectroscopy, ultraviolet-visible spectroscopy, and transmission electron microscopy indicates that the monolayer graphene derived from these carbon sources is of high quality.

Simple and Direct Analysis of Phytosterols in Red Palm Oil by Reverse Phase HPLC and Charged Aerosol Detection

Phytosterols (PSs) are a group of naturally occurring steroid alcohols found in plants. There is considerable interest in PSs as dietary supplements as they are reported to lower cholesterol levels and also have a positive impact on cardiovascular diseases. However, recent research suggests that PS supplementation may aggravate atherosclerosis and lead to aortic valve stenosis. PSs are typically measured by gas chromatography (GC), but this approach is time-consuming since it requires saponification of the sample, several extractions, and derivatization. We developed a simplified method using reversed-phase, HPLC and charged aerosol detection (CAD). CAD is sensitive, has a dynamic range of >4 orders of magnitude, can measure any non-volatile species, and analytes shows similar response independent of their chemical structure. Samples were prepared by simple dilution prior to analysis. Five PSs, campesterol, cholesterol, stigmasterol, beta-sitosterol, and stigmastanol, were resolved in <35min. Calibration curves showed linear correlation coefficients >0.997. The LOD was <=5ng (on column). Analysis of red palm oil is used as an example. The method is simple to use, has good linearity and sensitivity, and is capable of measuring numerous PSs in plant extracts. This approach can be used to examine product purity, supplement content, and adulteration.

Characterization and source apportionment of submicron aerosol with aerosol mass spectrometer during the PRIDE-PRD 2006 campaign

Abstract. Size-resolved chemical compositions of non-refractory submicron aerosol were measured using an Aerodyne quadrupole aerosol mass spectrometer (Q-AMS) at the rural site Back Garden (BG), located ~50 km northwest of Guangzhou in July 2006. This paper characterized the submicron aerosol particles of regional air pollution in Pearl River Delta (PRD) in the southern China. Organics and sulfate dominated the submicron aerosol compositions, with average mass concentrations of 11.8 ± 8.4 μg m−3 and 13.5 ± 8.7 μg m−3, respectively. Unlike other air masses, the air masses originated from Southeast-South and passing through the PRD urban areas exhibited distinct bimodal size distribution characteristics for both organics and sulfate: the first mode peaked at vacuum aerodynamic diameters (Dva) ∼200 nm and the second mode occurred at Dva from 300–700 nm. With the information from AMS, it was found from this study that the first mode of organics in PRD regional air masses was contributed by both secondary organic aerosol formation and combustion-related emissions, which is different from most findings in other urban areas (first mode of organics primarily from combustion-related emissions). The analysis of AMS mass spectra data by positive matrix factorization (PMF) model identified three sources of submicron organic aerosol including hydrocarbon-like organic aerosol (HOA), low volatility oxygenated organic aerosol (LV-OOA) and semi-volatile oxygenated organic aerosol (SV-OOA). The strong correlation between HOA and EC indicated primary combustion emissions as the major source of HOA while a close correlation between SV-OOA and semi-volatile secondary species nitrate as well as between LV-OOA and nonvolatile secondary species sulfate suggested secondary aerosol formation as the major source of SV-OOA and LV-OOA at the BG site. However, LV-OOA was more aged than SV-OOA as its spectra was highly correlated with the reference spectra of fulvic acid, an indicator of aged and oxygenated aerosol. The origin of HOA and OOA (the sum of LV-OOA and SV-OOA) has been further confirmed by the statistics that primary organic carbon (POC) and secondary organic carbon (SOC), estimated by the EC tracer method, were closely correlated with HOA and OOA, respectively. The results of the EC tracer method and of the PMF model revealed that primary organic aerosol (POA) constituted ~34–47 % of OA mass and secondary organic aerosol (SOA) constituted ~53–66 % of regional organic aerosol in PRD during summer season. The presence of abundant SOA was consistent with water soluble organic carbon (WSOC) results (accounting for ~60 % of OC on average) by Miyazaki et al. (2009) for the same campaign. OOA correlated well with WSOC at the BG site, indicating that most OOA were water soluble. More specifically, approximately 86 % of LV-OOA and 61 % of SV-OOA were estimated as water soluble species on the basis of carbon content comparison.

Organic condensation: a vital link connecting aerosol formation to cloud condensation nuclei (CCN) concentrations

Abstract. Atmospheric aerosol particles influence global climate as well as impair air quality through their effects on atmospheric visibility and human health. Ultrafine (&lt;100 nm) particles often dominate aerosol numbers, and nucleation of atmospheric vapors is an important source of these particles. To have climatic relevance, however, the freshly nucleated particles need to grow in size. We combine observations from two continental sites (Egbert, Canada and Hyytiälä, Finland) to show that condensation of organic vapors is a crucial factor governing the lifetimes and climatic importance of the smallest atmospheric particles. We model the observed ultrafine aerosol growth with a simplified scheme approximating the condensing species as a mixture of effectively non-volatile and semi-volatile species, demonstrate that state-of-the-art organic gas-particle partitioning models fail to reproduce the observations, and propose a modeling approach that is consistent with the measurements. We find that roughly half of the mass of the condensing mass needs to be distributed proportional to the aerosol surface area (thus implying that the condensation is governed by gas-phase concentration rather than the equilibrium vapour pressure) to explain the observed aerosol growth. We demonstrate the large sensitivity of predicted number concentrations of cloud condensation nuclei (CCN) to these interactions between organic vapors and the smallest atmospheric nanoparticles – highlighting the need for representing this process in global climate models.

Photochemistry of polycyclic aromatic hydrocarbons in cosmic water ice

Context. Mid-infrared emission features originating from polycyclic aromatic hydrocarbons (PAHs) are observed towards photon dominated regions in space. Towards dense clouds, however, these emission features are quenched. Observations of dense clouds show that many simple volatile molecules are frozen out on interstellar grains, forming thin layers of ice. Recently, observations have shown that more complex non-volatile species, presumably including PAHs, also freeze out and contribute to the ongoing solid-state chemistry.

Oligomer Content of α-Pinene Secondary Organic Aerosol

The quantity, extraction efficiency, and molecular composition of non-volatile oligomeric species in SOA generated by the reaction of α-pinene with ozone were studied. Two different methods of determining the total particulate mass in the reaction chamber were compared and found to be in good agreement when changes in the partitioning of semi-volatile compounds to the particle phase during measurement were properly handled. Almost all of the non-volatile organic carbon formed by the reaction was collected and recovered by extraction with organic solvents; recoveries with water extraction were somewhat lower. The identities of compounds extracted by the various solvents were determined using electrospray ionization Fourier transform ion cyclotron resonance (ESI-FTICR) mass spectrometry. Over 80% of the peaks weighted by mass and intensity were the same in the spectra of samples obtained from different extraction solvents. Standard addition plots were used to determine the amounts of two commercially available monomer compounds in the SOA extracts. When the response factors for those compounds were applied to other monomers detected in the mass spectra, the weight percent of monomers was estimated to be slightly less than 50%, with the remaining mass (over 50%) assigned to oligomers. The oligomer content is sufficiently large that it should be taken into account when modeling the formation and properties of laboratory SOA.