The application of thermal methods for determining chemical composition of carbonaceous aerosols: a review

A review of quantification methods for light absorption enhancement of black carbon aerosol

Black carbon (BC) is a distinct type of carbonaceous aerosol that has a significant impact on the environment, human health, and climate. A non-BC material coating on BC can alter the mixing state of the BC particles, which considerably enhances the mass absorption efficiency of BC by directing more energy toward the BC cores (lensing effect). A lot of methods have been reported for quantifying the enhancement factor (Eabs), with diverse results. However, to the best of our knowledge, a comprehensive review specific to the quantification methods for Eabs has not been systematically performed, which is unfavorable for the evaluation of obtained results and subsequent radiative forcing. In this review, quantification methods are divided into two broad categories, direct and indirect, depending on whether experimental removal of the coating layer from an aged carbonaceous particle is required. The direct methods described include thermal peeling, solvent dissolution, and optical virtual exfoliation, while the indirect methods include intercept-linear regression fitting, minimum R squared, numerical simulation, and empirical value. We summarized the principles, procedures, virtues, and limitations of the major Eabs quantification methods and analyzed the current problems in the determination of Eabs. We pointed out what breakthroughs are needed to improve or innovate Eabs quantification methods, particularly regarding the need to avoid the influence of brown carbon, develop a broadband Eabs quantification scheme, quantify the Eabs values for the emissions of low-efficiency combustions, measure the Eabs of particles in a high-humidity environment, design a real-time monitor of Eabs by a proper combination of mature techniques, and make more use of artificial intelligence for better Eabs quantification. This review deepens the understanding of Eabs quantification methods and benefits the estimation of the contribution of BC to radiative forcing using climate models.

Inter-laboratory comparison of plant volatile analyses in the light of intra-specific chemodiversity

INTRODUCTION

Assessing intraspecific variation in plant volatile organic compounds (VOCs) involves pitfalls that may bias biological interpretation, particularly when several laboratories collaborate on joint projects. Comparative, inter-laboratory ring trials can inform on the reproducibility of such analyses.

OBJECTIVES

In a ring trial involving five laboratories, we investigated the reproducibility of VOC collections with polydimethylsiloxane (PDMS) and analyses by thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS). As model plant we used Tanacetum vulgare, which shows a remarkable diversity in terpenoids, forming so-called chemotypes. We performed our ring-trial with two chemotypes to examine the sources of technical variation in plant VOC measurements during pre-analytical, analytical, and post-analytical steps.

METHODS

Monoclonal root cuttings were generated in one laboratory and distributed to five laboratories, in which plants were grown under laboratory-specific conditions. VOCs were collected on PDMS tubes from all plants before and after a jasmonic acid (JA) treatment. Thereafter, each laboratory (donors) sent a subset of tubes to four of the other laboratories (recipients), which performed TD-GC-MS with their own established procedures.

RESULTS

Chemotype-specific differences in VOC profiles were detected but with an overall high variation both across donor and recipient laboratories. JA-induced changes in VOC profiles were not reproducible. Laboratory-specific growth conditions led to phenotypic variation that affected the resulting VOC profiles.

CONCLUSION

Our ring trial shows that despite large efforts to standardise each VOC measurement step, the outcomes differed both qualitatively and quantitatively. Our results reveal sources of variation in plant VOC research and may help to avoid systematic errors in similar experiments.

An approach for carbon content measurement in marine sediment: Application of organic and elemental carbon analyzer

Organic and Elemental Carbon (OEC) is widely applied in the atmospheric sciences for determining carbon content and distinguishing black carbon contents of aerosols, with an advantage that OEC-based approach can provide thermograms derived from carbonaceous material. It is potential to adopt the advantage to measure the content and composition of organic carbon (OC)% in marine sediments. Here, we utilized the OEC analyzer to measure the OC% in marine sediment based on the pyrolytic oxidation principle, and obtain the OC-derived carbon dioxide (CO₂) thermograms. We examined marine sediments and reference materials to understand the stability and reproducibility of OC% measurements using our approach. The findings indicate that the OC% results (ranging from 1.44 to 1.59%, ave. 1.55 ± 0.03%, n = 64) based on this approach are accurate. In addition, CO₂ concentration thermograms obtained by repeated measurements exhibit a strong reproducibility. Our approach can thus provide the concentrations of thermally-evolved CO₂ with increasing heating temperature to deeply understand the reactivities of OC and the compositions in sediments. We suggest that the OEC-based OC% measurement is credible when samples preparation is well-performed (e.g., suitable sample mass and uniformly distributed loading). To sum up, we provide a means to accurately determine the OC% in marine sediments in terms of the ramped-pyrolysis principle.

Review of Filters for Air Sampling and Chemical Analysis in Mining Workplaces

This review considers the use of filters to sample air in mining workplace environments for dust concentration measurement and subsequent analysis of hazardous contaminants, especially respirable crystalline silica (RCS) on filters compatible with wearable personal dust monitors (PDM). The review summarizes filter vendors, sizes, costs, chemical and physical properties, and information available on filter modeling, laboratory testing, and field performance. Filter media testing and selection should consider the characteristics required for mass by gravimetry in addition to RCS quantification by Fourier-transform infrared (FTIR) or Raman spectroscopic analysis. For mass determination, the filters need to have high filtration efficiency (≥99% for the most penetrable particle sizes) and a reasonable pressure drop (up to 16.7 kPa) to accommodate high dust loading. Additional requirements include: negligible uptake of water vapor and gaseous volatile compounds; adequate particle adhesion as a function of particle loading; sufficient particle loading capacity to form a stable particle deposit layer during sampling in wet and dusty environments; mechanical strength to withstand vibrations and pressure drops across the filter; and appropriate filter mass compatible with the tapered element oscillating microbalance. FTIR and Raman measurements require filters to be free of spectral interference. Furthermore, because the irradiated area does not completely cover the sample deposit, particles should be uniformly deposited on the filter.

Apportionment of Vehicle Fleet Emissions by Linear Regression, Positive Matrix Factorization, and Emission Modeling

Real-world emission factors for different vehicle types and their contributions to roadside air pollution are needed for air-quality management. Tunnel measurements have been used to estimate emission factors for several vehicle types using linear regression or receptor-based source apportionment. However, the accuracy and uncertainties of these methods have not been sufficiently discussed. This study applies four methods to derive emission factors for different vehicle types from tunnel measurements in Hong Kong, China: (1) simple linear regressions (SLR); (2) multiple linear regressions (MLR); (3) positive matrix factorization (PMF); and (4) EMission FACtors for Hong Kong (EMFAC-HK). Separable vehicle types include those fueled by liquefied petroleum gas (LPG), gasoline, and diesel. PMF was the most useful, as it simultaneously seeks source profiles and source contributions. Diesel-, gasoline-, and LPG-fueled vehicle emissions accounted for 52%, 10%, and 5% of PM2.5 mass, respectively, while ammonium sulfate (~20%), ammonium nitrate (6%), and road dust (7%) were also large contributors. MLR exhibited the highest relative uncertainties, typically over twice those determined by SLR. EMFAC-HK has the lowest relative uncertainties due to its assumption of a single average emission factor for each pollutant and each vehicle category under specific conditions. The relative uncertainties of SLR and PMF are comparable.

Pt/Au Nanoparticles@Co3O4 Cataluminescence Sensor for Rapid Analysis of Methyl Sec-Butyl Ether Impurity in Methyl Tert-Butyl Ether Gasoline Additive

High purity methyl tert-butyl ether (MTBE) can be used to adjust gasoline octane values. However, an isomer, methyl sec-butyl ether (MSBE), is the main by-product of its industrial production, and this affects the purity of MTBE. Pt/Au NPs@Co3O4 composites with a hollow dodecahedron three-dimensional structure were synthesized using ZIF-67 as a template, with Pt and Au nanoparticles (NPs) evenly distributed on the shell of the hollow structure. A CTL sensor was established for the determination of MSBE based on the specificity of Pt/Au NPs@Co3O4. The experimental results showed that Pt/Au NPs@Co3O4 had a strong specific cataluminescence (CTL) response to MSBE, with no interference from MTBE. The linear range was 0.10–90 mg/L, the limit of detection was 0.031 mg/L (S/N = 3), the RSD was 2.5% (n = 9), and a complete sample test could be completed in five minutes. The sensor was used to detect MSBE in MTBE of different purity grades, with recoveries ranging from 92.0% to 109.2%, and the analytical results were consistent with those determined by gas chromatography. These results indicate that the established method was accurate and reliable, and could be used for rapid analysis of MTBE gasoline additive.

Chemical characteristics and sources of nitrogen-containing organic compounds at a regional site in the North China Plain during the transition period of autumn and winter

Organic nitrogen constitutes a significant fraction of the nitrogen budget in particulate matter (PM). However, the composition and sources of nitrogen-containing organic compounds (NOCs) in PM remain unclear currently in North China Plain (NCP), China. Rare local or regional studies on NOCs were conducted. In this study, ambient fine particles (PM_2.5) were collected in Xianghe, a regional background site in NCP, from 26 October to 26 December 2017. The insights from this study include NOC molecule identification, concentration level, and NOC sources and origins. Specifically, we have identified and quantified >90 NOC species, with urea being the most abundant, accounting for 39.7 ± 4.7% of the total NOC followed by free amino acids (FAAs; 21.9 ± 1.5%), cyclic NOCs (15.3 ± 4.5%), amines (14.8 ± 1.5%), alkyl amides (5.8 ± 0.5%), isocyanates (1.7 ± 0.2%), and nitriles (1.1 ± 0.2%). The time series of FAAs was well correlated (r = 0.51-0.68, p < 0.01) with the organic marker of levoglucosan and was moderately correlated with O_x (r = 0.29-0.41, p < 0.01), suggesting biomass burning and secondary formation were important FAAs sources. We also show that amines can be oxidized and/or reacted by aqueous-phase processing to form secondary aerosols, which are further enhanced by the involvement of iron in the catalytic process. Using the receptor model of positive matrix factorization (PMF), six factors were identified including coal combustion, crustal sources, biomass burning, industry-related sources, traffic emissions, and secondary aerosols. Source apportionment of NOC shows biomass burning was the dominant factor, accounting for 31.8% of the total NOCs. This study provides a unique dataset of NOCs at this regional background site in the NCP, with the insights of NOC chemical composition and sources gained in this study being important for future NOC modeling as well as NOC health effects studies.

Review of Respirable Coal Mine Dust Characterization for Mass Concentration, Size Distribution and Chemical Composition

Respirable coal mine dust (RCMD) exposure is associated with black lung and silicosis diseases in underground miners. Although only RCMD mass and silica concentrations are regulated, it is possible that particle size, surface area, and other chemical constituents also contribute to its adverse health effects. This review summarizes measurement technologies for RCMD mass concentrations, morphology, size distributions, and chemical compositions, with examples from published efforts where these methods have been applied. Some state-of-the-art technologies presented in this paper have not been certified as intrinsically safe, and caution should be exerted for their use in explosive environments. RCMD mass concentrations are most often obtained by filter sampling followed by gravimetric analysis, but recent requirements for real-time monitoring by continuous personal dust monitors (CPDM) enable quicker exposure risk assessments. Emerging low-cost photometers provide an opportunity for a wider deployment of real-time exposure assessment. Particle size distributions can be determined by microscopy, cascade impactors, aerodynamic spectrometers, optical particle counters, and electrical mobility analyzers, each with unique advantages and limitations. Different filter media are required to collect integrated samples over working shifts for comprehensive chemical analysis. Teflon membrane filters are used for mass by gravimetry, elements by energy dispersive X-ray fluorescence, rare-earth elements by inductively coupled plasma-mass spectrometry and mineralogy by X-ray diffraction. Quartz fiber filters are analyzed for organic, elemental, and brown carbon by thermal/optical methods and non-polar organics by thermal desorption-gas chromatography-mass spectrometry. Polycarbonate-membrane filters are analyzed for morphology and elements by scanning electron microscopy (SEM) with energy dispersive X-ray, and quartz content by Fourier-transform infrared spectroscopy and Raman spectroscopy.

An overview of methods of fine and ultrafine particle collection for physicochemical characterisation and toxicity assessments

Particulate matter (PM) is a crucial health risk factor for respiratory and cardiovascular diseases. The smaller size fractions, ≤2.5 μm (PM_2.5; fine particles) and ≤0.1 μm (PM_0.1; ultrafine particles), show the highest bioactivity but acquiring sufficient mass for in vitro and in vivo toxicological studies is challenging. We review the suitability of available instrumentation to collect the PM mass required for these assessments. Five different microenvironments representing the diverse exposure conditions in urban environments are considered in order to establish the typical PM concentrations present. The highest concentrations of PM_2.5 and PM_0.1 were found near traffic (i.e. roadsides and traffic intersections), followed by indoor environments, parks and behind roadside vegetation. We identify key factors to consider when selecting sampling instrumentation. These include PM concentration on-site (low concentrations increase sampling time), nature of sampling sites (e.g. indoors; noise and space will be an issue), equipment handling and power supply. Physicochemical characterisation requires micro- to milli-gram quantities of PM and it may increase according to the processing methods (e.g. digestion or sonication). Toxicological assessments of PM involve numerous mechanisms (e.g. inflammatory processes and oxidative stress) requiring significant amounts of PM to obtain accurate results. Optimising air sampling techniques are therefore important for the appropriate collection medium/filter which have innate physical properties and the potential to interact with samples. An evaluation of methods and instrumentation used for airborne virus collection concludes that samplers operating cyclone sampling techniques (using centrifugal forces) are effective in collecting airborne viruses. We highlight that predictive modelling can help to identify pollution hotspots in an urban environment for the efficient collection of PM mass. This review provides guidance to prepare and plan efficient sampling campaigns to collect sufficient PM mass for various purposes in a reasonable timeframe.

Coupling Filter-Based Thermal Desorption Chemical Ionization Mass Spectrometry with Liquid Chromatography/Electrospray Ionization Mass Spectrometry for Molecular Analysis of Secondary Organic Aerosol

Filter-based thermal desorption (F-TD) techniques, such as the filter inlet for gases and aerosols, are widely employed to investigate the molecular composition and physicochemical properties of secondary organic aerosol (SOA). Here, we introduce an enhanced capability of F-TD through the combination of a customized F-TD inlet with chemical ionization mass spectrometry (CIMS) and ultraperformance liquid chromatography/electrospray ionization mass spectrometry (UPLC/ESI-MS). The utility of F-TD/CIMS + UPLC/ESI-MS is demonstrated by application to α-pinene ozonolysis SOA for which increased filter aerosol mass loading is shown to slow the evaporation rates of deposited compounds. Evidence for oligomer decomposition producing multimode F-TD/CIMS thermograms is provided by the measurement of the mass fraction remaining of monomeric and dimeric α-pinene oxidation products on the filter via UPLC/ESI-MS. In situ evaporation of aerosol particles suggests that α-pinene-derived hydroperoxides are thermally labile; thus, analysis of particle-phase (hydro)peroxides via F-TD may not be appropriate. A synthesized pinene-derived dimer ester (C₂₀H₃₂O₅) is found to be thermally stable up to 200 °C, whereas particle-phase dimers (C₁₉H₃₀O₅) are observed to form during F-TD analysis via thermally induced condensation of synthesized pinene-derived alcohols and diacids. The complementary F-TD/CIMS + UPLC/ESI-MS method offers previously inaccessible insight into the molecular composition and thermal desorption behavior of SOA that both clarifies and expands on analysis via traditional F-TD techniques.

The pattern and mechanism of air pollution in developed coastal areas of China: From the perspective of urban agglomeration

The green development of coastal urban agglomerations, which are strategic core areas of national economic growth in China, has become a major focus of both academics and government agencies. In this paper, China's coastal urban agglomeration is taken as the research area, aiming at the serious air pollution problem of coastal urban agglomeration, geographic information system (ArcGIS10.2) spatial analysis and the spatial Dubin model were applied to National Aeronautics and Space Administration atmospheric remote sensing image inversion fine particulate matter (PM2.5) data from 2010-2016 to reveal the temporal and spatial evolution characteristics and Influence mechanism of PM2.5 in China's coastal urban agglomerations, with a view to providing a reference value for coordinating air pollution in the coastal cities of the world. From 2010-2016, the PM2.5 concentration in China's coastal urban agglomerations decreased as a whole, and large spatial differences in PM2.5 concentration were observed in China's coastal urban agglomerations; the core high-pollution areas were the Beijing-Tianjin-Hebei, Shandong Peninsula, and Yangtze River Delta urban agglomerations. Large spatial differences in PM2.5 concentration were also observed within individual urban agglomerations, with higher PM2.5 concentrations found in the northern parts of the urban agglomerations. Significant spatial autocorrelation and spatial heterogeneity were observed among PM2.5-polluted cities in China's coastal urban agglomerations. The northern coastal urban agglomerations formed a relatively stable and continuous high-pollution zone. The spatial Dubin model was used to analyze the driving factors of PM2.5 pollution in coastal urban agglomerations. Together, meteorological, socioeconomic, pollution source, and ecological factors affected the spatial characteristics of PM2.5 pollution during the study period, and the overall effect was a mixed effect with significant spatial variation. Among them, meteorological factors were the greatest driver of PM2.5 pollution. In the short term, the rapid increase in population density, industrial emissions, industrial energy consumption, and total traffic emissions were the important driving factors of PM2.5 pollution in the coastal urban agglomerations of China.

Application of thermal desorption methods for airborne polycyclic aromatic hydrocarbon measurement: A critical review

Thermal desorption (TD) is a universal solvent-free pre-concentration technique. It is often used to pre-concentrate semi-volatile and volatile organic compounds in various sample types. Polycyclic aromatic hydrocarbons (PAHs) are widespread contaminants from incomplete combustion of organic matter and fossil fuel, which have carcinogenic effects on human health. Conventional methods for determining PAHs, represented by solvent extraction, are gradually being replaced by solvent-free methods, typically the TD technique, because of TD's many advantages, including time savings and environmentally friendly treatment. This work presents an extensive review of the universal methods used to determine PAHs in the atmosphere based on the TD technique. The methods currently used for collection and detection of both gas- and particle-phase PAHs in the air are critically reviewed. In addition, the operating parameters of the TD unit are summarized and discussed. The design shortcomings of existing studies and the problems that researchers should address are presented, and promising alternatives are suggested. This paper also discusses important parameters, such as reproducibility and limit of detection, that form a crucial part of quality assurance. Finally, the limitations and the future prospects of the TD technique for use in airborne PAH analyses are addressed. This is the first review of the latest developments of the TD technique for analysis of PAHs and their derivatives in the atmosphere.

Carbonaceous Particulate Matter Emitted from a Pellet-Fired Biomass Boiler

Biomass pellets are a source of renewable energy; although, the air pollution and exposure risks posed by the emissions from burning pellets in biomass boilers (BBs) are uncertain. The present study examines the organic species in fine particle matter (PM) emissions from an BB firing switchgrass (SwG) and hardwood (HW) biomass pellets using different test cycles. The organic and elemental carbon (OC and EC) content and select semivolatile organic compounds (SVOCs) in filter-collected PM were identified and quantified using thermal-optical analysis and gas chromatography–mass spectrometry (GC–MS), respectively. Fine PM emissions from the BB ranged from 0.4 g/kg to 2.91 g/kg of pellets burned of which 40% ± 17% w/w was carbon. The sum of GC–MS quantified SVOCs in the PM emissions varied from 0.13 to 0.41 g/g OC. Relatively high levels of oxygenated compounds were observed in the PM emissions, and the most predominant individual SVOC constituent was levoglucosan (12.5–320 mg/g OC). The effect of boiler test cycle on emissions was generally greater than the effect due to pellet fuel type. Organic matter emissions increased at lower loads, owing to less than optimal combustion performance. Compared with other types of residential wood combustion studies, pellet burning in the current BB lowered PM emissions by nearly an order of magnitude. PM emitted from burning pellets in boilers tested across multiple studies also contains comparatively less carbon; however, the toxic polycyclic aromatic hydrocarbons (PAH) in the PM tested across these pellet-burning studies varied substantially, and produced 2–10 times more benzo[k]fluoranthene, dibenz[a,h]anthracene and indeno[1,2,3-c,d]pyrene on average. These results suggest that further toxicological evaluation of biomass pellet burning emissions is required to properly understand the risks posed.

Metal-organic frameworks for the sorption of acetone and isopropanol in exhaled breath of diabetics prior to quantitation by gas chromatography

A method is described for non-invasive glucose monitoring of diabetics by means of breath analysis. The metal-organic frameworks (MOFs) ZIF-7, UiO-66 and MOF-5 were chosen as sorbents in packed tubes for sampling and preconcentration of acetone and isopropanol which are established diabetes biomarkers. The MOF UiO-66 was found to be the most appropriate sorbent. Following thermal desorption, acetone and isopropanol where quantified by GC. The method has low limits of detection (0.79-0.84 μg·L^-1) and wide linear ranges (5-2000 μg·L^-1). It is assumed that the good performance of UiO-66 as a sorbent results from its large surface area and unique porous structure, and from van der Waals interactions. The relative standard deviation for six replicate cycles of sampling and preconcentration using one 50 mg UiO-66 packed tube ranged between 2.3 and 6.7% for intra-day assays, and from 2.7 to 4.3% for inter-day assays. A tube packed with 50 mg of UiO-66 packed tube can be used in over 120 cycles of adsorption/desorption without significant loss of collection efficiency. The GC method has been applied for the analysis of diabetic breath samples, and the recoveries from spiked samples ranged from 89.1 to 107.6%. Graphical abstract Schematic presentation of metal-organic frameworks as sorbents combined with thermal desorption-gas chromatography for the determination of acetone and isopropanol in exhaled breath of diabetics.

Personal exposure to PM2.5-bound organic species from domestic solid fuel combustion in rural Guanzhong Basin, China: Characteristics and health implication

Domestic solid fuels combustion produces a mass of fine particulate matter (PM_2.5). PM_2.5-bound organics, including polycyclic aromatic hydrocarbons (PAHs), oxygenated-PAHs (OPAHs), phthalate esters (PAEs) and hopanes, were quantified in indoor, outdoor and personal exposure samples collected in rural Guanzhong Basin, China. The average concentration of total quantified PAHs in personal exposure samples was 310 ± 443 ng m^-3, 1.5 times of those of indoor (211 ± 120 ng m^-3) and outdoor (189 ± 115 ng m^-3). Similar observations were found for the OPAHs and PAEs, i.e., much higher concentrations were seen in personal exposure samples. Hopanes average personal exposure concentration (13 ± 9.7 ng m^-3) was comparable to indoors (15 ± 9.7 ng m^-3) and outdoors (13 ± 9.6 ng m^-3). Among four common heating ways applied in Chinese dwelling, the highest exposure levels to PAHs, OPAHs and PAEs were found for indoor coal chunks stoves. Concentration under electric power was 1.2-4.5 folds lower than those with solid fuels in this study, proved to be the cleanest energy for the household heating. The exposures to PM_2.5 on cell viabilities were also investigated. The largest reduction of 70% on cell viabilities was seen for indoor coal chunks stove housewives, indicating that the emissions from coal combustion had the greatest cytotoxic effects. The results evidenced that the heating ways in rural area could greatly impact on the housewife health in northwestern China. Advanced heating technology and protection should be conducted to reduce the personal exposures to PM_2.5 from domestic solid fuel combustions.

Contribution of Fine Particles to Air Emission at Different Phases of Biomass Burning

Particle size distribution in biomass smoke was observed for different burning phases, including flaming and smouldering, during the combustion of nine common Australian vegetation representatives. Smoke particles generated during the smouldering phase of combustions were found to be coarser as compared to flaming aerosols for all hard species. In contrast, for leafy species, this trend was inversed. In addition, the combustion process was investigated over the entire duration of burning by acquiring data with one second time resolution for all nine species. Particles were separately characterised in two categories: fine particles with dominating diffusion properties measurable with diffusion-based instruments (Dp < 200 nm), and coarse particles with dominating inertia (Dp > 200 nm). It was found that fine particles contribute to more than 90 percent of the total fresh smoke particles for all investigated species.

Multivariate Optimization of Tenax TA-Thermal Extraction for Determining Gaseous Phase Organophosphate Esters in Air Samples

Suitable conditions for thermal extraction of semi-volatile organic compounds have largely been arrived at by univariate optimization or based on the recommendations provided by the manufacturers of the extraction equipment. Herein, we demonstrated the multivariate optimization of Tenax TA–thermal extraction for determining organophosphate esters in the gas phase fraction of air samples. Screening and refining experiments were performed using the eighth fraction factorial and Box-Behnken designs, respectively, and satisfactory models were obtained. Subsequently, the process was optimized by Derringer’s desirability function and the global desirability was 0.7299. Following optimization, the analytes were desorbed at 290 °C for 10 minutes at a helium flow of 95 mL min⁻¹, with the transfer line set at 290 °C. The analytes were then cryofocused at 20 °C and then cryodesorbed into the chromatographic column at 295 °C for 6 minutes. Method validation exhibited high linearity coefficients (>0.99), good precision (CV < 14%) and low detection limits (0.1–0.5 ng m⁻³). The method was tested by pumping 0.024 m³ of real indoor environment air through Tenax TA sorbent tubes. Furthermore, with multivariate optimization, analysis time and other resources were significantly reduced, and information about experimental factor interaction effects was investigated, as compared to the univariate optimization and other traditional methods.

Fine-Scale Source Apportionment Including Diesel-Related Elemental and Organic Constituents of PM2.5 across Downtown Pittsburgh

Health effects of fine particulate matter (PM_2.5) may vary by composition, and the characterization of constituents may help to identify key PM_2.5 sources, such as diesel, distributed across an urban area. The composition of diesel particulate matter (DPM) is complicated, and elemental and organic carbon are often used as surrogates. Examining multiple elemental and organic constituents across urban sites, however, may better capture variation in diesel-related impacts, and help to more clearly separate diesel from other sources. We designed a “super-saturation” monitoring campaign of 36 sites to capture spatial variance in PM_2.5 and elemental and organic constituents across the downtown Pittsburgh core (~2.8 km²). Elemental composition was assessed via inductively-coupled plasma mass spectrometry (ICP-MS), organic and elemental carbon via thermal-optical reflectance, and organic compounds via thermal desorption gas-chromatography mass-spectrometry (TD-GCMS). Factor analysis was performed including all constituents—both stratified by, and merged across, seasons. Spatial patterning in the resultant factors was examined using land use regression (LUR) modelling to corroborate factor interpretations. We identified diesel-related factors in both seasons; for winter, we identified a five-factor solution, describing a bus and truck-related factor [black carbon (BC), fluoranthene, nitrogen dioxide (NO₂), pyrene, total carbon] and a fuel oil combustion factor (nickel, vanadium). For summer, we identified a nine-factor solution, which included a bus-related factor (benzo[ghi]fluoranthene, chromium, chrysene, fluoranthene, manganese, pyrene, total carbon, total elemental carbon, zinc) and a truck-related factor (benz[a]anthracene, BC, hopanes, NO₂, total PAHs, total steranes). Geographic information system (GIS)-based emissions source covariates identified via LUR modelling roughly corroborated factor interpretations.

Spatial Patterns in Rush-Hour vs. Work-Week Diesel-Related Pollution across a Downtown Core

Despite advances in monitoring and modelling of intra-urban variation in multiple pollutants, few studies have attempted to separate spatial patterns by time of day, or incorporated organic tracers into spatial monitoring studies. Due to varying emissions sources from diesel and gasoline vehicular traffic, as well as within-day temporal variation in source mix and intensity (e.g., rush-hours vs. full-day measures), accurately assessing diesel-related air pollution within an urban core can be challenging. We allocated 24 sampling sites across downtown Pittsburgh, Pennsylvania (2.8 km²) to capture fine-scale variation in diesel-related pollutants, and to compare these patterns by sampling interval (i.e., “rush-hours” vs. “work-week” concentrations), and by season. Using geographic information system (GIS)-based methods, we allocated sampling sites to capture spatial variation in key traffic-related pollution sources (i.e., truck, bus, overall traffic densities). Programmable monitors were used to collect integrated work-week and rush-hour samples of fine particulate matter (PM_2.5), black carbon (BC), trace elements, and diesel-related organics (polycyclic aromatic hydrocarbons (PAHs), hopanes, steranes), in summer and winter 2014. Land use regression (LUR) models were created for PM_2.5, BC, total elemental carbon (EC), total organic carbon (OC), elemental (Al, Ca, Fe), and organic constituents (total PAHs, total hopanes), and compared by sampling interval and season. We hypothesized higher pollution concentrations and greater spatial contrast in rush-hour, compared to full work-week samples, with variation by season and pollutant. Rush-hour sampling produced slightly higher total PM_2.5 and BC concentrations in both seasons, compared to work-week sampling, but no evident difference in spatial patterns. We also found substantial spatial variability in most trace elements and organic compounds, with comparable spatial patterns using both sampling paradigms. Overall, we found higher concentrations of traffic-related trace elements and organic compounds in rush-hour samples, and higher concentrations of coal-related elements (e.g., As, Se) in work-week samples. Mean bus density was the strongest LUR predictor in most models, in both seasons, under each sampling paradigm. Within each season and constituent, the bus-related terms explained similar proportions of variance in the rush-hour and work-week samples. Rush-hour and work-week LUR models explained similar proportions of spatial variation in pollutants, suggesting that the majority of emissions may be produced during rush-hour traffic across downtown. Results suggest that rush-hour emissions may predominantly shape overall spatial variance in diesel-related pollutants.

Chemical characterization of PM2.5 from a southern coastal city of China: applications of modeling and chemical tracers in demonstration of regional transport

An intensive sampling campaign of airborne fine particles (PM_2.5) was conducted at Sanya, a coastal city in Southern China, from January to February 2012. Chemical analyses and mass reconstruction were used identify potential pollution sources and investigate atmospheric reaction mechanisms. A thermodynamic model indicated that low ammonia and high relative humidity caused the aerosols be acidic and that drove heterogeneous reactions which led to the formation of secondary inorganic aerosol. Relationships among neutralization ratios, free acidity, and air-mass trajectories suggest that the atmosphere at Sanya was impacted by both local and regional emissions. Three major transport pathways were identified, and flow from the northeast (from South China) typically brought the most polluted air to Sanya. A case study confirmed strong impact from South China (e.g., Pearl River Delta region) (contributed 76.8% to EC, and then this result can be extended to primary pollutants) when the northeast winds were dominant. The Weather Research Forecasting Black carbon model and trace organic markers were used to apportion local pollution versus regional contributions. Results of the study offer new insights into the atmospheric conditions and air pollution at this coastal city.

Evaluation on exposures to particulate matter at a junior secondary school: a comprehensive study on health risks and effective inflammatory responses in Northwestern China

Air pollutant measurement and respiratory inflammatory tests were conducted at a junior secondary school in Xi'an, Northwestern China. Hazardous substances including particulate matters (PMs), black carbon (BC) and particle-bounded polycyclic aromatic hydrocarbons (PAHs) were quantified both indoors and outdoors of the school. Source characterization with organic tracers and particle-size distribution demonstrated that the school's air was mostly polluted by combustion emissions from the surrounding environment. The evaluation of health assessment related to air quality was conducted by two methods, including potential risk estimation of air pollutants and direct respiratory inflammatory test. The incremental lifetime cancer risks associated with PAHs were estimated and were 1.62 × 10^-6 and 2.34 × 10^-6, respectively, for indoor and outdoor fine PMs. Both the values exceeded the threshold value of 1 × 10^-6, demonstrating that the carcinogenic PAHs are a health threat to the students. Respiratory inflammatory responses of 50 students who studied in the sample classroom were examined with a fractional exhaled nitric oxide (FeNO) test, with the aid of health questionnaires. The average FeNO concentration was 17.4 ± 8.5 ppb, which was slightly lower than the recommended level of 20 ppb established by the American Thoracic Society for children. However, a wide distribution and 6% of the values were > 35 ppb, suggesting that the potentials were still high for eosinophilic inflammation and responsiveness to corticosteroids. A preliminary interpretation of the relationship between air toxins and respiratory inflammatory response demonstrated the high exposure cancer risks and inflammatory responses of the students to PMs in the city.

Source, health risk and composition impact of outdoor very fine particles (VFPs) to school indoor environment in Xi'an, Northwestern China

Very fine particles (VFPs, PM_0.25) are able to travel deeply into the respiratory tract and can produce adverse health effects, especially to children. Information on the VFPs in schools is generally lacking. We investigated the chemical compositions, sources and health risks of VFPs in a junior secondary school of Xi'an, China, during May 16th to 30th, 2012. The results showed that organic matter (37% and 39%), SO₄^2- (13% and 11%) and geological material (20% and 24%) were the major components of VFPs both outdoors and indoors. The VFP species indoors, such as SO₄^2- and elemental carbon, are mainly from outdoor origins, e.g. coal burning and traffic emissions. But particle resuspension by student activities, chalk dust and import from outdoors of soil dust also contributed to deteriorate air quality in the classroom. By contrast to outdoors, several indoor factors, like higher room temperature, limited volume and longer suspension time of classroom particles, can even lead to significant secondary pollutant production. Heavy metals (mainly from outside) bound to indoor VFPs are supposedly associated to non-cancer health risks, especially Pb through ingestion pathway and Mn through dermal contact. Outdoor VFPs may be associated to PAHs cancer health risks via inhalation way. This study confirms that both indoor and outdoor sources had contributions to indoor VFPs, and that VFPs health risk should be of higher concern in urban areas of Northwestern China.

Evaluation of thermal optical analysis method of elemental carbon for marine fuel exhaust

The awareness of black carbon (BC) as the second largest anthropogenic contributor in global warming and an ice melting enhancer has increased. Due to prospected increase in shipping especially in the Arctic reliability of BC emissions and their invented amounts from ships is gaining more attention. The International Maritime Organization (IMO) is actively working toward estimation of quantities and effects of BC especially in the Arctic. IMO has launched work toward constituting a definition for BC and agreeing appropriate methods for its determination from shipping emission sources. In our study we evaluated the suitability of elemental carbon (EC) analysis by a thermal-optical transmittance (TOT) method to marine exhausts and possible measures to overcome the analysis interferences related to the chemically complex emissions. The measures included drying with CaSO_4, evaporation at 40-180ºC, H₂O treatment, and variation of the sampling method (in-stack and diluted) and its parameters (e.g., dilution ratio, Dr). A reevaluation of the nominal organic carbon (OC)/EC split point was made. Measurement of residual carbon after solvent extraction (TC-C_SOF) was used as a reference, and later also filter smoke number (FSN) measurement, which is dealt with in a forthcoming paper by the authors. Exhaust sources used for collecting the particle sample were mainly four-stroke marine engines operated with variable loads and marine fuels ranging from light to heavy fuel oils (LFO and HFO) with a sulfur content range of <0.1-2.4% S. The results were found to be dependent on many factors, namely, sampling, preparation and analysis method, and fuel quality. It was found that the condensed H₂SO₄ + H₂O on the particulate matter (PM) filter had an effect on the measured EC content, and also promoted the formation of pyrolytic carbon (PyC) from OC, affecting the accuracy of EC determination. Thus, uncertainty remained regarding the EC results from HFO fuels.

IMPLICATIONS

The work supports one part of the decision making in black carbon (BC) determination methodology. If regulations regarding BC emissions from marine engines will be implemented in the future, a well-defined and at best unequivocal method of BC determination is required for coherent and comparable emission inventories and estimating BC effects. As the aerosol from marine emission sources may be very heterogeneous and low in BC, special attention to the effects of sampling conditions and sample pretreatments on the validity of the results was paid in developing the thermal-optical analysis methodology (TOT).

Air quality measurements-From rubber bands to tapping the rainbow

It is axiomatic that good measurements are integral to good public policy for environmental protection. The generalized term for "measurements" includes sampling and quantitation, data integrity, documentation, network design, sponsorship, operations, archiving, and accessing for applications. Each of these components has evolved and advanced over the last 200 years as knowledge of atmospheric chemistry and physics has matured. Air quality was first detected by what people could see and smell in contaminated air. Gaseous pollutants were found to react with certain materials or chemicals, changing the color of dissolved reagents such that their light absorption at selected wavelengths could be related to both the pollutant chemistry and its concentration. Airborne particles have challenged the development of a variety of sensory devices and laboratory assays for characterization of their enormous range of physical and chemical properties. Advanced electronics made possible the sampling, concentration, and detection of gases and particles, both in situ and in laboratory analysis of collected samples. Accurate and precise measurements by these methods have made possible advanced air quality management practices that led to decreasing concentrations over time. New technologies are leading to smaller and cheaper measurement systems that can further expand and enhance current air pollution monitoring networks.

IMPLICATIONS

Ambient air quality measurement systems have a large influence on air quality management by determining compliance, tracking trends, elucidating pollutant transport and transformation, and relating concentrations to adverse effects. These systems consist of more than just instrumentation, and involve extensive support efforts for siting, maintenance, calibration, auditing, data validation, data management and access, and data interpretation. These requirements have largely been attained for criteria pollutants regulated by National Ambient Air Quality Standards, but they are rarely attained for nonroutine measurements and research studies.

Spatial variation in diesel-related elemental and organic PM2.5 components during workweek hours across a downtown core

Capturing intra-urban variation in diesel-related pollution exposures remains a challenge, given its complex chemical mix, and relatively few well-characterized ambient-air tracers for the multiple diesel sources in densely-populated urban areas. To capture fine-scale spatial resolution (50×50m grid cells) in diesel-related pollution, we used geographic information systems (GIS) to systematically allocate 36 sampling sites across downtown Pittsburgh, PA, USA (2.8km²), cross-stratifying to disentangle source impacts (i.e., truck density, bus route frequency, total traffic density). For buses, outbound and inbound trips per week were summed by route and a kernel density was calculated across sites. Programmable monitors collected fine particulate matter (PM_2.5) samples specific to workweek hours (Monday-Friday, 7 am-7 pm), summer and winter 2013. Integrated filters were analyzed for black carbon (BC), elemental carbon (EC), organic carbon (OC), elemental constituents, and diesel-related organic compounds [i.e., polycyclic aromatic hydrocarbons (PAHs), hopanes, steranes]. To our knowledge, no studies have collected this suite of pollutants with such high sampling density, with the ability to capture spatial patterns during specific hours of interest. We hypothesized that we would find substantial spatial variation for each pollutant and significant associations with key sources (e.g. diesel and gasoline vehicles), with higher concentrations near the center of this small downtown core. Using a forward stepwise approach, we developed seasonal land use regression (LUR) models for PM_2.5, BC, total EC, OC, PAHs, hopanes, steranes, aluminum (Al), calcium (Ca), and iron (Fe). Within this small domain, greater concentration differences were observed in most pollutants across sites, on average, than between seasons. Higher PM_2.5 and BC concentrations were found in the downtown core compared to the boundaries. PAHs, hopanes, and steranes displayed different spatial patterning across the study area by constituent. Most LUR models suggested a strong influence of bus-related emissions on pollution gradients. Buses were more dominant predictors compared to truck and vehicular traffic for several pollutants. Overall, we found substantial variation in diesel-related concentrations in a very small downtown area, which varied across elemental and organic components.

Microscale spatial distribution and health assessment of PM2.5-bound polycyclic aromatic hydrocarbons (PAHs) at nine communities in Xi'an, China

Spatial variability of polycyclic aromatic hydrocarbons (PAHs) associated with fine particulate matter (PM_2.5) was investigated in Xi'an, China, in summer of 2013. Sixteen priority PAHs were quantified in 24-h integrated air samples collected simultaneously at nine urban and suburban communities. The total quantified PAHs mass concentrations ranged from 32.4 to 104.7 ng m^-3, with an average value of 57.1 ± 23.0 ng m^-3. PAHs were observed higher concentrations at suburban communities (average: 86.3 ng m^-3) than at urban ones (average: 48.8 ng m^-3) due to a better enforcement of the pollution control policies at the urban scale, and meanwhile the disorganized management of motor vehicles and massive building constructions in the suburbs. Elevated PAH levels were observed in the industrialized regions (west and northwest of Xi'an) from Kriging interpolation analysis. Satellite-based visual interpretations of land use were also applied for the supporting the spatial distribution of PAHs among the communities. The average benzo[a]pyrene-equivalent toxicity (Σ[BaP]_eq) at the nine communities was 6.9 ± 2.2 ng m^-3 during the sampling period, showing a generally similar spatial distribution to PAHs levels. On average, the excess inhalation lifetime cancer risk derived from Σ[BaP]_eq indicated that eight persons per million of community residents would develop cancer due to PM_2.5-bound PAHs exposure in Xi'an. The great in-city spatial variability of PAHs confirmed the importance of multiple points sampling to conduct exposure health risk assessment.

Characterization of PM2.5 in Guangzhou, China: uses of organic markers for supporting source apportionment

Organic carbon (OC), elemental carbon (EC), and non-polar organic compounds including n-alkanes (n-C14-n-C40), polycyclic aromatic hydrocarbons (PAHs), phthalate esters (PAEs) and hopanes were quantified in fine particulate (PM2.5), which were collected in urban area of Guangzhou, China in winter and summer in 2012/2013. The pollutants levels were well comparable with the data obtained in previous studies in Pearl River Delta (PRD) region but much lower than most northern Chinese megacities. The contribution of EC to PM2.5 and OC/EC ratio suggest that the pollution sources were relatively consistent in GZ between the two seasons. Benzo[a]pyrene (BaP) was the most abundant PAHs, which were 4.9 and 1.0ng/m(3) on average, accounting for 10.7% and 9.1% to the total quantified PAHs in winter and summer, respectively. The total concentrations of PAEs ranged from 289.1 to 2435ng/m(3) and from 102.4 to 1437ng/m(3), respectively, in winter and summer. Di-n-butyl phthalate (DBP) was the most dominant PAEs. The ambient levels of PAEs could be partly attributed to the widespread uses of the household products, municipal garbage compressing, sewage, and external painting material on the building. Source apportionment for OC with chemical mass balance (CMB) model demonstrated coal combustion, vehicle emission, cooking, and secondary organic compounds (SOC) formation were the four major pollution sources. Both of the indices of n-alkanes and diagnostic PAHs ratios support that anthropogenic sources such as vehicle emission and coal combustion were the significant pollution sources with some extents from epicuticular waxes by terrestrial plants. The ratio of hopanes to EC proved the influences from vehicle emission, and displayed a certain degree of the air aging in the Guangzhou ambient air.

Inter-annual variability of wintertime PM2.5 chemical composition in Xi'an, China: Evidences of changing source emissions

Chemical characteristics of PM2.5 in Xi'an in wintertime of 2006, 2008, and 2010 were investigated. Markers of OC2, EC1, and NO3(-)/SO4(2-) ratio were calculated to investigate the changes in PM2.5 emission sources over the 5-year period. Positive matrix factorization (PMF) model was used to identify and quantify the main sources of PM2.5 and their contributions. The results showed that coal combustion, motor vehicular emissions, fugitive dust, and secondary inorganic aerosol accounted for more than 80% of PM2.5 mass. The importance of these major sources to the PM2.5 mass varied yearly: coal combustion was the largest contributor (31.2% ± 5.2%), followed by secondary inorganic aerosol (20.9% ± 5.2%) and motor vehicular emissions (19.3% ± 4.8%) in 2006; the order was still coal combustion emissions (27.6% ± 3.4%), secondary inorganic aerosol (23.2% ± 6.9%), and motor vehicular emissions (20.9% ± 4.6%) in 2008; while coal combustion emission further decreased (24.1% ± 3.1%) with fugitive dust (19.4% ± 5.5%) increasing in 2010. The changes in PM2.5 chemical compositions and source contributions can be attributed to the social and economic developments in Xi'an, China, including energy structure adjustment, energy consumption, the expansion of civil vehicles, and the increase of urban construction activities.

Health effects of carbon-containing particulate matter: focus on sources and recent research program results

Air pollution is a complex mixture of gas-, vapor-, and particulate-phase materials comprised of inorganic and organic species. Many of these components have been associated with adverse health effects in epidemiological and toxicological studies, including a broad spectrum of carbonaceous atmospheric components. This paper reviews recent literature on the health impacts of organic aerosols, with a focus on specific sources of organic material; it is not intended to be a comprehensive review of all the available literature. Specific emission sources reviewed include engine emissions, wood/biomass combustion emissions, biogenic emissions and secondary organic aerosol (SOA), resuspended road dust, tire and brake wear, and cooking emissions. In addition, recent findings from large toxicological and epidemiological research programs are reviewed in the context of organic PM, including SPHERES, NPACT, NERC, ACES, and TERESA. A review of the extant literature suggests that there are clear health impacts from emissions containing carbon-containing PM, but difficulty remains in apportioning responses to certain groupings of carbonaceous materials, such as organic and elemental carbon, condensed and gas phases, and primary and secondary material. More focused epidemiological and toxicological studies, including increased characterization of organic materials, would increase understanding of this issue.

Characterization of PM2.5 and PM10 fugitive dust source profiles in the Athabasca Oil Sands Region

Geological samples were collected from 27 representative locations in the Athabasca Oil Sands Region (AOSR) in Alberta, Canada. These samples were resuspended onto filter substrates for PM2.5 and PM10 size fractions. Samples were analyzed for 229 chemical species, consisting of elements, ions, carbon, and organic compounds. These chemical species are normalized to gravimetric mass to derive individual source profiles. Individual profiles were grouped into six categories typical of those used in emission inventories: paved road dust, unpaved road dust close to and distant from oil sand operations, overburden soil, tailings sands, and forest soils. Consistent with their geological origin, the major components are minerals, organic and elemental carbon, and ions. The sum of five major elements (i.e., Al, Si, K, Ca, and Fe) and their oxidized forms account for 25-40% and 45-82% of particulate matter (PM) mass, respectively. Si is the most abundant element, averaging 17-18% in the Facility (oil sand operations) and 23-27% in the Forest profiles. Organic carbon is the second most abundant species, averaging 9-11% in the Facility and 5-6% in the Forest profiles. Elemental carbon abundance is 2-3 times higher in Facility than Forest profiles. Sulfate abundance is ~7 times higher in the Facility than in the Forest profiles. The ratios of cation/anion and base cation (sum of Na+, Mg2+, K+, and Ca2+)/nitrogen- and sulfur-containing ions (sum of NH4+, NO2-, NO3-, and SO4(2-)) exceed unity, indicating that the soils are basic. Lead (Pb) isotope ratios of facility soils are similar to the AOSR stack and diesel emissions, while those of forest soils have much lower 206Pb/207Pb and 208Pb/207Pb ratios. High-molecular-weight n-alkanes (C25-C40), hopanes, and steranes are more than an order of magnitude more abundant in Facility than Forest profiles. These differences may be useful for separating anthropogenic from natural sources of fugitive dust at receptors.

IMPLICATIONS

Several organic compounds typical of combustion emissions and bitumen are enriched relative to forest soils for fugitive dust sources near oil sands operations, consistent with deposition uptake by biomonitors. AOSR dust samples are alkaline, not acidic, indicating that potential acid deposition is neutralized. Chemical abundances are highly variable within emission inventory categories, implying that more specific subcategories can be defined for inventory speciation.

Characteristics and major sources of carbonaceous aerosols in PM2.5 from Sanya, China

PM2.5 samples were collected in Sanya, China in summer and winter in 2012/2013. Organic carbon (OC), elemental carbon (EC), and non-polar organic compounds including n-alkanes (n-C14-n-C40) and polycyclic aromatic hydrocarbons (PAHs) were quantified. The concentrations of these carbonaceous matters were generally higher in winter than summer. The estimated secondary organic carbon (OCsec) accounted for 38% and 54% of the total organic carbon (TOC) in winter and summer, respectively. The higher value of OCsec in addition to the presences of photochemically-produced PAHs in summer supports that photochemical conversions of organics are much active at the higher air temperatures and with stronger intense solar radiation. Carbon preference index (CPI) and percent contribution of wax n-alkanes suggest that anthropogenic sources were more dominant than derivation from terrestrial plants in Sanya. Diagnostic ratios of atmospheric PAHs further indicate that there was a wide mix of pollution sources in winter while fossil fuel combustion was the most dominant in summer. Positive Matrix Factorization (PMF) analysis with 18 PAHs in the winter samples found that motor vehicle emissions and biomass burning were the two main pollution sources, contributing 37.5% and 24.6% of the total quantified PAHs, respectively.

Source and risk apportionment of selected VOCs and PM₂.₅ species using partially constrained receptor models with multiple time resolution data

This study was conducted to identify and quantify the sources of selected volatile organic compounds (VOCs) and fine particulate matter (PM2.5) by using a partially constrained source apportionment model suitable for multiple time resolution data. Hourly VOC, 12-h and 24-h PM2.5 speciation data were collected during three seasons in 2013. Eight factors were retrieved from the Positive Matrix Factorization solutions and adding source profile constraints enhanced the interpretability of source profiles. Results showed that the evaporative emission factor was the largest contributor (25%) to VOC mass concentration, while the largest contributor to PM2.5 mass concentration was soil dust/regional transport related factor (26%). In terms of risk prioritization, traffic/industry related factor was the major cause for benzene, ethylbenzene, Cr, and polycyclic aromatic hydrocarbons (29-69%) while petrochemical related factor contributed most to the Ni risk (36%). This indicated that a larger contributor to mass concentration may not correspond to a higher risk.

Concentrations, particle-size distributions, and indoor/outdoor differences of polycyclic aromatic hydrocarbons (PAHs) in a middle school classroom in Xi'an, China

Polycyclic aromatic hydrocarbons (PAHs) attached to particulate matter can affect respiratory health, especially the health of children, but information on the air quality in schools is generally lacking. This study investigated the PAH concentrations in a naturally ventilated classroom in Xi'an, China, from 16 to 31 May 2012. Particulate PAH concentrations were measured for samples collected on five-stage cascade impactors deployed inside the classroom and outside. PM2.5-bound PAH concentrations were 53.2 ng m(-3) indoors and 72.9 ng m(-3) outdoors. PAHs attached to very fine particles (VFPs) accounted for ~70% of the total PAHs. The PAH concentrations indoors were affected by the students' activities, cleaning, and smoking, while outdoors, the main sources were motor vehicle emissions and contaminated road dust. Particle-bound PAHs infiltrated the classroom through open windows, but the activities of the students and staff were also associated with an increase of PAHs attached to particles larger than 1.0 µm, most likely through resuspension. Cycles in the sources led to PAH concentrations 2-3 times higher on weekdays compared to weekends, both indoors and outdoors. PAH toxicity risks inside the classroom were substantially lower than those outdoors, and the highest risks were associated with VFPs.

PM2.5 source apportionment with organic markers in the Southeastern Aerosol Research and Characterization (SEARCH) study

Positive matrix factorization (PMF) and effective variance (EV) solutions to the chemical mass balance (CMB) were applied to PM(2.5) (particulate matter with an aerodynamic diameter <2.5 μm) mass and chemically speciated measurements for samples taken from 2008 to 2010 at the Atlanta, Georgia, and Birmingham, Alabama, sites. Commonly measured PM(2.5) mass, elemental, ionic, and thermal carbon fraction concentrations were supplemented with detailed nonpolar organic speciation by thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS). Source contribution estimates were calculated for motor vehicle exhaust, biomass burning, cooking, coal-fired power plants, road dust, vegetative detritus, and secondary sulfates and nitrates for Atlanta. Similar sources were found for Birmingham, with the addition of an industrial source and the separation of biomass burning into open burning and residential wood combustion. EV-CMB results based on conventional species were qualitatively similar to those estimated by PMF-CMB. Secondary ammonium sulfate was the largest contributor, accounting for 27-38% of PM(2.5), followed by biomass burning (21-24%) and motor vehicle exhaust (9-24%) at both sites, with 4-6% of PM(2.5) attributed to coal-fired power plants by EV-CMB. Including organic compounds in the EV-CMB reduced the motor vehicle exhaust and biomass burning contributions at both sites, with a 13-23% deficit for PM(2.5) mass. The PMF-CMB solution showed mixing of sources within the derived factors, both with and without the addition of speciated organics, as is often the case with complex source mixtures such as those at these urban-scale sites. The nonpolar TD-GC/MS compounds can be obtained from existing filter samples and are a useful complement to the elements, ions, and carbon fractions. However, they should be supplemented with other methods, such as TD-GC/MS on derivitized samples, to obtain a wider range of polar compounds such as sterols, sugars, and organic acids. The PMF and EV solutions to the CMB equations are complementary to, rather than replacements for, each other, as comparisons of their results reveal uncertainties that are not otherwise evident.

IMPLICATIONS

Organic markers can be measured on currently acquired PM(2.5) filter samples by thermal methods. These markers can complement element, ion, and carbon fraction measurements from long-term speciation networks. Applying the positive matrix factorization and effective variance solutions for the chemical mass balance equations provides useful information on the accuracy of the source contribution estimates. Nonpolar compounds need to be complemented with polar compounds to better apportion cooking and secondary organic aerosol contributors.

FTIR analysis of surface functionalities on particulate matter produced by off-road diesel engines operating on diesel and biofuel

Fourier transform infrared spectroscopy is applied as a powerful analytic technique for the evaluation of the chemical composition of combustion aerosols emitted by off-road engines fuelled by diesel and biofuels. Particles produced by burning diesel, heated rapeseed oil (RO), RO with ethylhexylnitrate, and heated palm oil were sampled from exhausts of representative in-use diesel engines. Multicomponent composition of diesel and biofuel particles reveal the chemistry related to a variety of functional groups containing carbon, hydrogen, oxygen, sulfur, and nitrogen. The most intensive functionalities of diesel particles are saturated C-C-H and unsaturated C=C-H aliphatic groups in alkanes and alkenes, aromatic C=C and C=C-H groups in polyaromatics, as well as sulfates and nitrated ions. The distinguished features of biofuel particles were carbonyl C=O groups in carboxylic acids, ketones, aldehydes, esters, and lactones. NO2, C-N and -NH groups in nitrocompounds and amines are found to dominate biofuel particles. Group identification is confirmed by complementary measurements of organic carbon (OC), elemental carbon, and water-soluble ion species. The relationship between infrared bands of polar oxygenated and non-polar aliphatic functionalities indicates the higher extent of the surface oxidation of biofuel particles. Findings provide functional markers of organic surface structure of off-road diesel emission, allowing for a better evaluation of relation between engine, fuel, operation condition, and particle composition, thus improving the quantification of environmental impacts of alternative energy source emissions.

Emission factors for gases and particle-bound substances produced by firing lead-free small-caliber ammunition

Lead-free ammunition is becoming increasingly popular because of the environmental and human health issues associated with the use of leaded ammunition. However, there is a lack of data on the emissions produced by firing such ammunition. We report emission factors for toxic gases and particle-bound compounds produced by firing lead-free ammunition in a test chamber. Carbon monoxide, ammonia, and hydrogen cyanide levels within the chamber were analysed by Fourier transform infrared spectroscopy, while total suspended particles and respirable particles were determined gravimetrically. The metal content of the particulate emissions was determined and the associated organic compounds were characterized in detail using a method based on thermal desorption coupled to gas chromatography and mass spectrometry. The particulate matter (∼30 mg/round) consisted primarily of metals such as Cu, Zn, and Fe along with soot arising from incomplete combustion. Nitrogen-containing heterocyclic aromatic compounds such as carbazole, quinolone, and phenazine were responsible for some of the 25 most significant chromatographic peaks, together with PAHs, diphenylamine, and phthalates. Emission factors were determined for PAHs and oxygenated PAHs; the latter were less abundant in the gun smoke particles than in domestic dust and diesel combustion smoke. This may be due to the oxygen-deficient conditions that occur when the gun is fired. By using an electrical low pressure impactor, it was demonstrated that more than 90% of the particles produced immediately after firing the weapon had diameters of less than 30 nm, and so most of the gun smoke particles belonged to the nanoparticle regime.

Organic constituents on the surfaces of aerosol particles from Southern Finland, Amazonia, and California studied by vibrational sum frequency generation

This article summarizes and compares the analysis of the surfaces of natural aerosol particles from three different forest environments by vibrational sum frequency generation. The experiments were carried out directly on filter and impactor substrates, without the need for sample preconcentration, manipulation, or destruction. We discuss the important first steps leading to secondary organic aerosol (SOA) particle nucleation and growth from terpene oxidation by showing that, as viewed by coherent vibrational spectroscopy, the chemical composition of the surface region of aerosol particles having sizes of 1 μm and lower appears to be close to size-invariant. We also discuss the concept of molecular chirality as a chemical marker that could be useful for quantifying how chemical constituents in the SOA gas phase and the SOA particle phase are related in time. Finally, we describe how the combination of multiple disciplines, such as aerosol science, advanced vibrational spectroscopy, meteorology, and chemistry can be highly informative when studying particles collected during atmospheric chemistry field campaigns, such as those carried out during HUMPPA-COPEC-2010, AMAZE-08, or BEARPEX-2009, and when they are compared to results from synthetic model systems such as particles from the Harvard Environmental Chamber (HEC). Discussions regarding the future of SOA chemical analysis approaches are given in the context of providing a path toward detailed spectroscopic assignments of SOA particle precursors and constituents and to fast-forward, in terms of mechanistic studies, through the SOA particle formation process.

Mass spectrometry of atmospheric aerosols--recent developments and applications. Part I: Off-line mass spectrometry techniques

Many of the significant advances in our understanding of atmospheric particles can be attributed to the application of mass spectrometry. Mass spectrometry provides high sensitivity with a fast response time to probe chemically complex particles. This review focuses on recent developments and applications in the field of mass spectrometry of atmospheric aerosols. In Part I of this two-part review, we concentrate on off-line mass spectrometry techniques, which require sample collection on filters but can provide detailed molecular speciation. In particular, off-line mass spectrometry techniques utilizing tandem mass spectrometry experiments and high resolution mass analyzers provide improved insight into secondary organic aerosol formation and heterogeneous reaction pathways through detailed structural elucidation at the molecular level.