Charring characteristics of atmospheric organic particulate matter in thermal analysis

The charring of organic materials during carbon analysis bythermal methods makes it difficult to differentiate elemental carbon (EC) from organic carbon (OC). Failure to correct for charring results in the overestimation of EC and the underestimation of OC. The charring characteristics andthermal behaviors of aerosol OC are studied by subjecting hexane and water extracts of ambient aerosols to various analysis conditions. The complete evolution of water-soluble organic carbon (WSOC) aerosol materials is found to require a temperature as high as 850 degrees C and the presence of oxygen. EC would be oxidized under these thermal conditions as well. As a result, thermal methods relying only on temperature for the differentiation of EC and OC would give unreliable OC and EC concentrations. Our investigation also reveals that WSOC accounts for a large fraction (13-66%) of charring, while hexane extractable organic compounds produce little charring. The extent of charring from WSOC, defined as the ratio between pyrolytically generated EC to the total WSOC, is found to increase with the WSOC loading in each analysis when the loadings are below a certain value. This ratio remains constant when the loadings are above this value. This may account for the high variability in the extent of charring among aerosol samples from different locations as well as among samples from a single location collected at different times. Charring is reduced if the residence time at each temperature step in a helium atmosphere is sufficiently long to allow for maximum C evolution at each step. Charring is also influenced by the presence of inorganic constituents such as ammonium bisulfate. For the few tested organic materials, it is observed that ammonium bisulfate enhances the charring of starch and cellulose but reduces the charring of levoglucosan.     

Peer reviewed: options for characterizing organic particulate matter

New research strategies could help elucidate the mechanisms and causes of aerosol health effects.     

Chemical compositions of fine particulate organic matter emitted from Chinese cooking

Food cooking can be a significant source of atmospheric particulate organic matter. In this study, the chemical composition of particulate organic matter (POM) in PM2.5 emitted from four different Chinese cooking styles were examined by gas chromotography-mass spectrometry (GC-MS). The identified species are consistent in the emissions from different Chinese cooking styles and the quantified compounds account for 5-10% of total POM in PM2.5. The dominant homologue is fatty acids, constituting 73-85% of the quantified compounds. The pattern of n-alkanes and the presence of beta-sitosterol and levoglucosan indicate that vegetables are consumed during Chinese cooking operations. Furthermore, the emissions of different compounds are impacted significantly by the cooking ingredients. The candidates of organic tracers used to describe and distinguish emissions from Chinese cooking in Guangzhou are tetradecanoic acid, hexadecanoic acid, octadecanoic acid, oleic acid, levoglucosan, mannosan, galactosan, nonanal, and lactones. During the sampling period, the relative contribution of Chinese cooking to the mass concentration of atmospheric hexadecanoic acid should be less than 1.3% in Guangzhou.     

Binding of 2,4,6-trinitrotoluene, aniline, and nitrobenzene to dissolved and particulate soil organic matter

The distribution of TNT* (the sum of TNT and its degradation products), aniline, and nitrobenzene between particulate organic matter (POM), dissolved soil organic matter (DOM), and free compound was studied in controlled kinetic (with and without irradiation) and equilibrium experiments with mixtures of POM and DOM reflecting natural situations in organic rich soils. The binding of TNT* to POM was fast, independent of irradiation, and adsorption isotherms had a great linear contribution (as determined by a mixed model), indicative of a hydrophobic partitioning mechanism. The binding of TNT* to DOM was slower, strongly enhanced under nonirradiated conditions, and adsorption isotherms were highly nonlinear, indicative of a specific interaction between TNT derivatives and functional groups of DOM. Nitrobenzene was associated to both POM and DOM via hydrophobic partitioning, whereas aniline binding was dominated by specific binding to POM and DOM functional groups. On the basis of nitrobenzene and TNT* adsorption parameters determined by a mixed Langmuir + linear model, POM had 2-3 times greater density of hydrophobic moieties as compared to DOM. This difference was reflected by a greater (O + N)/C atomic ratio for DOM. The sum of C-C and C-H moieties, as determined by X-ray photoelectron spectroscopy (XPS), and the sum of aryl-C and alkyl-C, as determined by solid-state cross-polarization magic-angle spinning (CP-MAS) 13C NMR, could only qualitatively account for differences in adsorption parameters. Aliphatic C was found to be more important for the hydrophobic partitioning than aromatic C. On the basis of nonlinear adsorption parameters,the density of functional groups reactive with aniline and TNT derivatives was 1.3-1.4 times greater in DOM than in POM, which was in fair agreement with 13C NMR and XPS data for the sum of carboxyl and carbonyl groups as potential sites for electrostatic and covalent bonding. We conclude that in contaminated soils characterized by continuous leaching of DOM, formation of TNT derivatives (via biotic and abiotic reductive degradation) and their preference for specific functional groups in DOM may contribute to a significant transportation of potentially toxic TNT compounds into surface waters and groundwaters.     

Fluorescence tracking of dissolved and particulate organic matter quality in a river-dominated estuary

Excitation-emission matrix (EEM) fluorescence was combined with parallel factor analysis (PARAFAC) to model base-extracted particulate (POM) and dissolved (DOM) organic matter quality in the Neuse River Estuary (NRE), North Carolina, before and after passage of Hurricane Irene in August 2011. Principle components analysis was used to determine that four of the PARAFAC components (C1-C3 and C6) were terrestrial sources to the NRE. One component (C4), prevalent in DOM of nutrient-impacted streams and estuaries and produced in phytoplankton cultures, was enriched in the POM and in surface sediment pore water DOM. One component (C5) was related to recent autochthonous production. Photoexposure of unfiltered Neuse River water caused an increase in slope ratio values (S(R)) which corresponded to an increase in the ratio C2:C3 for DOM, and the production of C4 fluorescence in both POM and DOM. Changes to the relative abundance of C4 in POM and DOM indicated that advection of pore water DOM from surface sediments into overlying waters could increase the autochthonous quality of DOM in shallow microtidal estuaries. Modeling POM and DOM simultaneously with PARAFAC is an informative technique that is applicable to assessments of estuarine water quality.     

Exposure to particulate matter,volatile organic compounds,and other air pollutants inside patrol cars

People driving in a vehicle might receive an enhanced dose of mobile source pollutants that are considered a potential risk for cardiovascular diseases. The exposure to components of air pollution in highway patrol vehicles, at an ambient, and a roadside location was determined during 25 work shifts (3 p.m. to midnight) in the autumn of 2001, each day with two cars. A global positioning system and a diary provided location and activity information. Average pollutant levels inside the cars were low compared to ambient air quality standards: carbon monoxide 2.7 ppm, nitrogen dioxide 41.7 microg/m3, ozone 11.7 ppb, particulate matter smaller 2.5 microm (PM2.5) 24 microg/m3. Volatile organic compounds inside the cars were in the ppb-range and showed the fingerprint of gasoline. PM2.5 was 24% lower than ambient and roadside levels, probably due to depositions associated with the recirculating air conditioning. Levels of carbon monoxide, aldehydes, hydrocarbons, and some metals (Al, Ca, Ti, V, Cr, Mn, Fe, Cu, and Sr) were highest in the cars, and roadside levels were higher than ambient levels. Elevated pollutant levels were related to locations with high traffic volumes. Our results point to combustion engine emissions from other vehicles as important sources of air pollutants inside the car.     

Partitioning of CPs, PCDEs, and PCDD/Fs between particulate and experimentally enhanced dissolved natural organic matter in a contaminated soil

We determined the distribution of hydrophobic organic contaminants (HOCs) to fractions of natural organic matter in a soil contaminated by chlorophenol wood preservatives more than 30 years ago. The concentration of dissolved organic matter (DOM) was enhanced in soil suspensions by raising pH to 6.8-9.1. After 48 h of desorption/equilibration, the DOM fraction was separated from the particulate organic matter (POM) of the soil by filtration. In the next step, DOM was flocculated by Al-nitrate, and free concentrations of HOCs were determined in the aqueous phase. The HOCs associated with DOM and POM were extracted with toluene. No significant differences in gross carbon chemistry were detected between DOM and POM, using X-ray photoelectron spectroscopy (XPS). Normalized to organic C, chlorophenols (CPs) showed a similar degree of partitioning between DOM and POM, whereas the partitioning of polychlorinated diphenyl ethers (PCDEs), polychlorinated dibenzo-p-dioxins, and furans (PCDD/Fs) was highly shifted toward POM. The partitioning to POM, relative to DOM, increased in the order PCDE < PCDF < PCDD, reflecting the hydrophobicity of the compounds.     

Trimethylsilyl derivatives of organic compounds in source samples and in atmospheric fine particulate matter

Source sample extracts of vegetative detritus, motor vehicle exhaust, tire dust paved road dust, and cigarette smoke have been silylated and analyzed by GC-MS to identify polar organic compounds that may serve as tracers for those specific emission sources of atmospheric fine particulate matter. Candidate molecular tracers were also identified in atmospheric fine particle samples collected in the San Joaquin Valley of California. A series of normal primary alkanols, dominated by even carbon-numbered homologues from C26 to C32, the secondary alcohol 10-nonacosanol, and some phytosterols are prominent polar compounds in the vegetative detritus source sample. No new polar organic compounds are found in the motor vehicle exhaust samples. Several hydrogenated resin acids are present in the tire dust sample, which might serve as useful tracers for those sources in areas that are heavily impacted by motor vehicle traffic. Finally, the alcohol and sterol emission profiles developed for all the source samples examined in this project are scaled according to the ambient fine particle mass concentrations attributed to those sources by a chemical mass balance receptor model that was previously applied to the San Joaquin Valley to compute the predicted atmospheric concentrations of individual alcohols and sterols. The resulting underprediction of alkanol concentrations at the urban sites suggests that alkanols may be more sensitive tracers for natural background from vegetative emissions (i.e., waxes) than the high molecular weight alkanes, which have been the best previously available tracers for that source.     

Sugars--dominant water-soluble organic compounds in soils and characterization as tracers in atmospheric particulate matter

The presence of saccharides is being reported for aerosols taken in urban, rural, and marine locales. The commonly found primary saccharides are alpha- and beta-glucose, alpha- and beta-fructose, sucrose, and mycose with lesser amounts of other monosaccharides. Saccharide polyols are also found in some airsheds and consist mainly of sorbitol, xylitol, mannitol, erythritol, and glycerol. In temperate climate areas these compounds increase from negligible concentrations in winter aerosols (usually dominated by levoglucosan and related anhydrosaccharides from biomass burning) to a maximum in late spring-summer, followed by a decrease to winter. The composition of the saccharide mixtures suggests soil and associated microbiota as the source. Saccharide analyses of soils confirmed these compositions. Therefore, we propose resuspension of soil (also unpaved road dust) from agricultural activities as a major component of aerosol particles and the saccharides are the source specific tracers. In addition, the saccharides as well as the anhydrosaccharide derivatives from biomass burning are completely water soluble and thus contribute significantly to the total water-soluble mass of aerosols.     

Variation in the sensitivity of predicted levels of atmospheric organic particulate matter (OPM)

This study examines the sensitivity in predicted levels of atmospheric organic particulate matter (M(o), microg m(-3)) to changes in the governing gas/particle partitioning constants and the tau(I) (levels of condensable organic compounds, microg m(-3)). M(o) is given by the difference between sigma tau(i) and the corresponding sum for the gas-phase levels. It is demonstrated that the sensitivity in predicted M(o) levels increases rapidly as M(o) becomes very small relative to sigma tau(i): as the tau(i), decrease, the gas phase becomes increasingly capable of holding the majority of all tau(i) and small changes in system parameters can cause large relative changes in M(o). These effects are illustrated using predictions for two values of the reacted hydrocarbon concentration (deltaHC) for each of three secondary organic aerosol systems for relative humidity (RH) = 20-80%. Specific structures for the oxidation products allows consideration of the effects of varying activity coefficients and water uptake. At low M(o)/sigma tau(i) (as may be found in the atmosphere away from sources and at warm temperatures), relatively small errors in model input parameters (e.g., vapor pressures, vaporization enthalpies, activity coefficient parameters, and the tau(i) values for low volatility compounds) will be amplified into large errors in the predicted M(o) values.     

烟叶类型、部位及生态区对总粒相物中主要有机酸释放量的影响

采用溶剂萃取-硅烷化衍生-GC-MS/MS法测定了卷烟主流烟气总粒相物中42种挥发半挥发有机酸（包括13种短链脂肪酸、7种中链脂肪酸、10种长链脂肪酸、12种其他有机酸）,按照单位燃烧烟丝量计算释放量。结果表明:①香料烟短链和中链脂肪酸释放量最高,烤烟中长链脂肪酸释放量最高,白肋烟各种脂肪酸释放量均不突出;②挥发半挥发有机酸释放量总体上随部位降低呈降低趋势;③按八大典型生态区划分,武夷生态区烟叶大部分挥发半挥发有机酸单位燃烧烟丝量释放量最高。      

Emission rates of particulate matter and elemental and organic carbon from in-use diesel engines

Elemental carbon (EC), organic carbon (OC), and particulate matter (PM) emission rates are reported for a number of heavy heavy-duty diesel trucks (HHDDTs) and back-up generators (BUGs) operating under real-world conditions. Emission rates were determined using a unique mobile emissions laboratory (MEL) equipped with a total capture full-scale dilution tunnel connected directly to the diesel engine via a snorkel. This paper shows that PM, EC, and OC emission rates are strongly dependent on the mode of vehicle operation; highway, arterial, congested, and idling conditions were simulated by following the speed trace from the California Air Resources Board HHDDT cycle. Emission rates for BUGs are reported as a function of engine load at constant speed using the ISO 8178B Cycle D2. The EC, OC, and PM emission rates were determined to be highly variable for the HHDDTs. It was determined that the per mile emission rate of OC from a HHDDT in congested traffic is 8.1 times higher than that of an HHDDT in cruise or highway speed conditions and 1.9 times higher for EC. EC/OC ratios for BUGs (which generally operate at steady states) and HHDDTs show marked differences, indicating that the transient nature of engine operation dictates the EC/OC ratio. Overall, this research shows that the EC/OC ratio varies widely for diesel engines in trucks and BUGs and depends strongly on the operating cycle. The findings reported here have significant implications in the application of chemical mass balance modeling, diesel risk assessment, and control strategies such as the Diesel Risk Reduction Program.     

Determination of chloroacetates in atmospheric particulate matter

Chloroacetates (CAAs) are ubiquitous in the environment. This study presents chloroacetates level in atmospheric particulate matter (APM) collected at Athens center. CAAs have been derivatized to their respective propyl esters and determined by gas chromatography (GC) with electron capture detection (ECD). Monochloroacetate (MCA) was the most abundant, followed by dichloroacetate (DCA) and trichloroacetate (TCA). Concentration values range from 3.0 to 8240 ng g(-1) (0.6-2010 pg m(-3)). Correlations to meteorological and pollution parameters are discussed, indicating that car exhausts may be a direct or indirect source of MCA, but origin from natural marine sources may also be relevant.     

Chemical characterization of ambient particulate matter near the World Trade Center: elemental carbon, organic carbon, and mass reconstruction

Concentrations of elemental carbon (EC), organic carbon matter (OM), particulate matter less than 2.5 microm (PM2.5), reconstructed soil, trace element oxides, and sulfate are reported from four locations near the World Trade Center (WTC) complex for airborne particulate matter (PM) samples collected from September 2001 through January 2002. Across the four sampling sites, daily mean concentrations ranged from 1.5 to 6.8 microg/m3 for EC, from 10.2 to 31.4 microg/m3 for OM, and from 22.6 to 66.2 microg/m3 for PM2.5. Highest concentrations of PM species were generally measured north and west of the WTC complex. Total carbon matter and sulfate constituted the largest fraction of reconstructed PM2.5 concentrations. Concentrations of PM species across all sites decreased from the period when fires were present at the WTC complex (before December 19, 2001) to the period after the fires. Averaged over all sites, concentrations decreased by 25.6 microg/m3 for PM2.5, 2.7 microg/m3 for EC, and 9.2 microg/m3 for OM from the fire period to after fire period.     

Recovery of semivolatile organic compounds during sample preparation: implications for characterization of airborne particulate matter

Semivolatile compounds present special analytical challenges not met by conventional methods for analysis of ambient particulate matter (PM). Accurate quantification of PM-associated organic compounds requires validation of the laboratory procedures for recovery over a wide volatility and polarity range. To meet these challenges, solutions of n-alkanes (nC12-nC40) and polycyclic aromatic hydrocarbons PAHs (naphthalene to benzo[ghi]perylene) were reduced in volume from a solvent mixture (equal volumes of hexane, dichloromethane and methanol), to examine recovery after reduction in volume. When the extract solution volume reached 0.5 mL the solvent was entirely methanol, and the recovery averaged 60% for n-alkanes nC12-nC25 and PAHs from naphthalene to chrysene. Recovery of higher MW compounds decreased with MW, because of their insolubility in methanol. When the walls of the flasks were washed with 1 mL of equal parts hexane and dichloromethane (to reconstruct the original solvent composition), the recovery of nC18 and higher MW compounds increased dramatically, up to 100% for nC22-nC32 and then slowly decreasing with MW due to insolubility. To examine recovery during extraction of the components of the High Capacity Integrated Gas and Particle Sampler, the same standards were used to spike its denuders and filters. For XAD-4 coated denuders and filters, normalized recovery was >95% after two extractions. Recovery from spiked quartz filters matched the recovery from the coated surfaces for alkanes nC18 and larger and for fluoranthene and larger PAHs. Lower MW compounds evaporated from the quartz filter with the spiking solvent. This careful approach allowed quantification of organics by correcting for volatility- and solubility-related sample preparation losses. This method is illustrated for an ambient sample collected with this sampler during the Texas Air Quality Study 2000.     

非挥发性有机酸与卷烟主流烟气总粒相物pH关系研究

以国内具有代表性的卷烟为研究对象,分别对卷烟样品的非挥发性有机酸含量和卷烟主流烟气粒相物pH进行了测定,通过数学分析研究了非挥发性有机酸含量对烟气粒相物pH的影响.主流烟气粒相物pH值评价指标与有机酸的关联分析结果表明,苹果酸、十五酸、油酸对主流烟气粒相物pH值相对影响较大.对影响主流烟气粒相物pH值的11种非挥发性有机酸的主成分分析结果表明,亚油酸,油酸,苹果酸,棕榈酸,草酸和亚麻酸对主流烟气粒相物pH值相对影响较大.综上可得,苹果酸和油酸对主流烟气粒相物pH值具有较大影响.