Diesel emissions contain complex mixtures of chemical constituents that are known to be (or possibly to be) human carcinogens, or that have adverse health effects . Among these substances (formaldehyde, benzene, acrolein, dioxins, etc.), polycyclic aromatic hydrocarbons (PAHs) and their nitrated derivatives (nitro-PAHs) have been implicated as major contributors to the toxicity of diesel exhausts [2, 3]. However, these substances are currently non-regulated pollutants in engine exhaust. PAHs are a group of organic compounds consisting of two or more fused aromatic rings, which are produced as a result of the incomplete combustion of fossil fuels. These compounds are mainly derived from anthropogenic sources, particularly from mobile sources of emissions in urban areas . The combustion of fuel in diesel engines results in the formation of a mixture of gaseous compounds (CO, CO2, NO, NO2, SO2, etc.) and solid particles (carbonaceous matter, sulphates, trace metals, etc.). PAHs and their derivatives can be found in the gaseous or particulate phases of diesel exhaust fumes depending on their vapour pressure, but the distribution of particles between the two phases is also dependent on the total amount of particles, on the physical characteristics of the particles (particularly their specific surface area), and on the temperature.
The majority of particulate matter in diesel exhaust is composed of fine particles that are primarily formed from the condensation of organic matter on an elemental carbon core. These particles are generally called soot particles. The soluble organic fraction (SOF) is defined as the fraction that can be extracted from soot using an organic solvent; particulate PAHs and their derivatives are found in this fraction. The SOF primarily originates from unburned fuel and engine lubrication oil . There is a wide range of SOF in the diesel particulate matter; it can range from less than 10 % to more than 90 % by soot mass. The fraction of SOF in the particulate matter depends on the type of diesel vehicles (light or heavy-duty diesel vehicles, mopeds, etc.), on the concentrations of sulfur and aromatic compounds in the diesel fuel, on the test engine cycles and also, on the collecting procedure of diesel exhaust, which is less well described. In general, the SOF values are highest for light engine loads when exhaust temperatures are low .
Two methods are generally used for measuring vehicle emissions: dynamometer studies where tailpipe fumes are measured from one vehicle, and roadside or tunnel studies where mean traffic emissions values (daily, by vehicles, etc.) are obtained . In this book chapter, only analytical methodologies developed for diesel emissions studies using dynamometer tests are described. Even if the exhaust particles produced in the tailpipe are distinct from those sampled in the ambient atmosphere, it is shown in this chapter that the trapping media are very similar. Conventional and less conventional sampling trains for collecting the particles are described. The classical (Soxhlet and ultra-sound extractions) and more recent methodologies (micro-wave assisted extractions, pressurised solvent extractions, supercritical fluid extractions, and solid phase extractions) are detailed; they are used for treating the collected samples from gaseous and particulate phases to obtain the fraction containing PAHs and their derivatives. Because the individual products present different health risks, information about total PAH emissions is less important than information about the composition of such emissions. Therefore, techniques that are developed for identifying and quantifying the individual PAHs and their nitrated derivatives found in the two phases are described.
Finally, the efficiency of the sample pretreatment step (before quantitation) is strongly dependent on the SOF fraction of diesel soot; therefore, it is shown in this chapter that when the optimisation of this important analytical step is neglected, it can lead to important analytical bias.
2. Properties, sources and toxicity of PAHs and nitro-PAHs
2.1. Physical and chemical properties of PAHs and nitro-PAHs
The name “polycyclic aromatic hydrocarbons” (PAH) commonly refers to a large class of organic compounds containing two or more fused aromatic rings; however, in a broad sense, non-fused ring systems should also be included. In particular, the term “PAH” refers to compounds containing only carbon and hydrogen atoms (
The physical and chemical properties of PAHs are dependent on the number of aromatic rings and on the molecular mass (Table 1). The smallest member of the PAH family is naphthalene, a two-ring compound, which is mainly found in the vapour phase in the atmosphere, because of its higher vapour pressure and Henry’s law constant KH (ratio between the partial pressure of a gas above a solution and the amount of gas solubilized in solution). Three to five ring-PAHs can be found in both the vapour and particulate phases in air. PAHs consisting of five or more rings tend to be solids adsorbed onto other particulate matter in the atmosphere. For instance, the resistance of PAHs to oxidation, reduction, and vaporisation increases with increasing molecular weight, whereas the aqueous solubility of these compounds decreases (their
|Compounds/||Chemical structure||Molecular mass|
Boiling points (°C)
(Pa at 25°C)
|Log Kow||Solubility in water at 25°C|
|KH at 25°C (Pa.m3 mol-1)|
|Naphthalene*||128.18||81 / 218||10.4||3.4||31.7||49|
|Acenaphtylene*||152.18||92 / 270||0.89||4.07||-||114|
|Acenaphthene*||154.21||95 / 279||0.29||3.92||3.9||15|
|Fluorene*||166.22||116 / 295||0.08||4.18||1.68||9.81|
|Anthracene*||178.24||216.4 / 342||8.0 10-4||4.5||0.073||73|
|Pyrene*||202.26||150.4 / 393||0.0006||5.18||0.135||1.1|
|Chrysene*||228.29||253.8 / 436||-||5.86||0.00179||0.53|
|228.29||160.7 / 400||2.8 10-5||5.61||0.014||1.22|
|252.32||168.3 / 481||-||5.78||0.0015||0.051|
|252.32||215.7 / 480||-||6.11||0.0008||0.044|
|Benzo[||252.32||178.1 / 496||7.3 10-7||6.50||0.004||0.034 (20°C)|
|Benzo[e]pyrene||252.32||178.7 / 493||7.4 10-7||6.44||0.005||-|
|Perylene||252.32||277.5 / 503||-||5.3||0.0004||-|
|276.34||278.3 / 545||1.4 10-8||7.10||0.00026||0.027 (20°C)|
|276.34||163.6 / -||-||-||0.00019||0.029 (20°C)|
|Coronene||300.36||439 / 525||2 10-10||5.4||0.00014||-|
|2-nitronaphthalene||173.17||74 / 304||3.2 10-2||2.78||26||610|
|2- nitrofluorene||211.22||154 / 326||9.7 10-5||3.37||0.216||95|
|9-nitroanthracene||223.23||146 / -||-||4.16||-||-|
|2-nitrophenanthrene||223.23||120 / -||-||4.23||-||-|
|2-nitrofluoranthene||247.25||- / 420||9.9 10-7||-||0.019||13|
|1-nitropyrene||247.25||152 / 472||4.4 10-6||5.29||0.017||64|
|2-nitropyrene||247.25||199 / 472||4.4 10-6||-||0.021||64|
|273.29||162 / -||-||5.34||-||-|
|6-nitro benzo[||297.31||260 / 567||-||6.13||-||12|
2.2. Toxicity of PAHs and nitroPAHs
Over 100 chemical compounds formed during the incomplete combustion of organic matter are classified as PAHs. These ubiquitous environmental pollutants are human carcinogens and mutagens; therefore, they are toxic to all living organisms. There are various pathways for human exposure to PAHs. For the general population, the major routes of exposure are from food and inhaled air; however, in smokers, the exposure from smoking and food may be of a similar magnitude. Extensive reviews and guidelines concerning PAHs contamination in food and air have been performed, and they have questioned the correct marker capable of following the risk assessment for the population .
There have been concerns regarding the carcinogenic effects of these products for at least two centuries, following the report of a high incidence of scrotal cancer in soot workers in London by Sir P. Pottwatched. The association between cancer and a specific chemical compound, Benz[
The increased attention to nitro-PAHs is due to their persistence in the environment and the higher mutagenic (2x105 times) and carcinogenic (10 times) properties of certain compounds compared to PAHs . Studies have highlighted the important role of nitro compounds, and they emphasised the necessity of improving primary prevention methods to reduce nitrated molecule air pollution. Today, the known sources of these types of compounds are a variety of combustion processes, especially in diesel engines. It was reported that the main contributors to the direct-acting mutagenicity of diesel exhaust particulates were nitro-PAHs, including 1,3-, 1,6- and 1,8-dinitropyrenes, 1-nitropyrene, 4-nitropyrene, and 6-nitrochrysene [15-18]. Therefore, researchers have investigated the chemical and physical properties of particulate matter in diesel exhaust according to the development of diesel technology and emissions regulation; comparisons between the fuel and engine used, such as diesel versus gasoline, light-duty diesel, biodiesel and any so called “clean diesel” have also been reported [19-23].
2.3. Contribution of mobiles sources to atmospheric emissions.
PAHs primarily originate in heavily urbanised or industrialised regions; therefore, the majority of these compounds are anthropogenic. Different sources of PAHs were reviewed and classified according to five main categories (domestic, mobile, industrial, agricultural and natural) . Domestic emissions are predominantly associated with the burning of coal, oil, gas, garbage, or other organic substances such as tobacco or char broiled meat. Mobile sources include the emission from vehicles such as aircraft, shipping vehicles, railways, automobiles, off-road vehicles, and machinery. Industrial sources of PAHs include primary aluminium production, coke production, creosote and wood preservation, waste
|PAH ratio||Value range||Source||References|
|Σ(low weight PAHs) / Σ(high weight PAHs)||<1|
Fossil fuel combustion
Grass, wood, coal combustion
Photolysis (ageing of particles)
Grass, wood, coal combustion
|B(b)FLT/B(k)FLT||2.5-2.9||Aluminium smelter emissions|
|Non traffic emissions|
incineration, cement manufacturing, petrochemical and related industries, bitumen and asphalt industries, rubber tire manufacturing, and commercial heat/power production. Agricultural sources include stubble burning, open burning of moorland heather for regeneration purposes, and open burning of brushwood and straw. With regard to the natural sources of PAHs from terrestrial sources (non-anthropogenic burning of forests, woodlands, and moorlands due to lightning strikes, volcanic eruptions) and cosmic origin, their contributions have been estimated as being negligible to the overall emission of PAHs. However, it is rather difficult to make accurate estimations of PAH emissions because some PAHs are common to a number of these sources, and it is not easy to quantitatively determine how much of a particular PAH comes from a specific source . Additionally, understanding the impact of particular emission sources on the different environmental compartments is crucial for proper risk assessment and risk management. PAHs are always emitted as a mixture, and the relative molecular concentration ratios are considered (often only as an assumption) to be characteristic of a given emission source. Table 2 lists typical diagnostic ratios taken from the literature that show the wide diversity of approaches .
Diagnostic ratios should be used with caution; the reactivity of some PAH species with other atmospheric species, such as ozone and/or oxides of nitrogen can change the diagnostic ratio [36-40]. The difference in chemical reactivity, volatility and solubility of PAH species may also introduce bias but to minimise this error, diagnostic ratios obtained from PAHs that have similar physico-chemical properties is mainly used . Regardless, vehicular emissions were shown to be a major source of PAHs, whether the diagnostic ratios were coupled or not with principle component analysis, and irrespective of the region or season involved; moreover, studies indicated that diesel exhausts were the largest source of PAHs and nitro-PAHs, compared with the emissions of the other vehicles [39-42].
3. Diesel exhaust collection, extraction and chemical analysis
Diesel exhaust contains not only volatile species, which constitute the gaseous phase, but also solid agglomerates of spherical primary particles of approximately 15-30 nm diameter. These agglomerates are larger particles, in the range 60-200 nm (with a lognormal size distribution), which are produced by an accumulation mode corresponding to a coagulation of the primary particles. The agglomerates are made of solids (elemental carbon and metallic ashes) mixed with condensates and adsorbed material (including organic hydrocarbons). The accumulation mode can be accompanied by a nucleation mode, which consists of smaller particles (which are called ultra-fine particles of 10-20 nm) where the organic material is condensed on primary inorganic nuclei (sulphuric acid) . It has been demonstrated that the ultra-fine particles are more easily volatilised, depending on temperature and dilution conditions, because they are mostly composed of volatile condensates and contain little solid material . Therefore, discriminating between the gaseous species and the chemical species present in the solid state in diesel exhausts remains difficult because their formation processes depend on the sampling train design, sampling location, temperature, humidity and dilution rates of exhausts, and also on after-treatment devices.
3.1. Exhaust sampling and collection for PAHs analysis
Numerous instruments are used to monitor and characterise particle-bound or gas-phase PAHs in diesel tailpipe emissions. To obtain reliable and reproducible measurements, it is necessary to properly design the sampling system and to choose adequate materials for trapping the chemical substances to be measured (filters, sorbents, etc.). The majority of experiments are performed on chassis dynamometers under predetermined engine load; a heated hose transfers the exhaust from the tailpipe to full flow exhaust dilution tunnels, and therefore, the exhaust gases are collected at low temperature after being mixed and homogenised with the ambient air (with moderate dilution ratios ranging from 6 to 14) in the dilution tunnel, which is connected to a constant volume sampling system (CVS technique) [45, 46]. Chassis dynamometers can also be equipped with dilution systems such as critical-flow Venturi dilution tunnels , ejection dilutors , or rotating disk diluters , but undiluted exhaust can also be directly collected through a sampling probe inserted inside the tailpipe, which is a less conventional method.
3.1.1. Collection of the gas phase
The supports used for trapping diesel gaseous exhaust are often the same as those used for air sampling; polyurethane foam plugs (PUF) of appropriate density can trap semivolatile contaminants in aerosols without creating excessive back pressure, and they are typically used to collect the atmospheric gaseous phase ; however, sorbents such as XAD-2 resins can also be used to trap the air gas fraction . XAD resins are nonionic macroporous polystyrene-divinylbenzene beads with macroreticular porosity and high surface areas, which give them their adsorptive characteristics for non-polar hydrophobic compounds such as PAHs or their derivatives. Therefore, we can also find these materials for the collection of semi-volatile PAHs and nitro-PAHs in the gas phase of diesel exhaust, because they are inexpensive and easy to handle, store and transport. Different adsorbent resins, such as XAD-2 or XAD-16, coupled to PUF cartridges (making “sandwiches” cartridges) can be used to collect PAHs in the gaseous phase [53-54]. The gaseous PAHs can also be collected using an annular denuder coated with different sorbents: the first stage is coated with XAD-4 resin, the second stage collects the particulate matter and the third stage is composed of a “sandwich” of polyurethane foam plugs and XAD-4 resin, to assess the volatilisation of PAHs from particles .
As previously mentioned, the vast majority of diesel exhaust is sampled in a dilution tunnel at low temperatures, where the condensation of the gaseous phase on solid particles is dominant. Additionally, operating at dilution ratios of approximately 10 is far from perfect because typical atmospheric dilution ratios are between 500 and 1000. A consequence is that the nucleation mode is favoured in the dilution tunnels where the saturation ratios are higher than those during atmospheric dilution, and the gaseous species coming out of the tailpipe are generally impoverished. However, one can be interested in the analysis of the gaseous exhaust at high temperature before the appearance of nucleation or condensation. A sampling method that differs from conventional collection methods was developed for this purpose and consists of trapping PAHs in an aqueous solution by gas bubbling and not on a solid sorbent. Therefore, when a particulate filter is incorporated after the diesel engine, the original method for trapping vapour-phase PAHs present in the hot undiluted gaseous exhaust is to absorb them inside an aqueous solution containing various additives, including a cationic surfactant as a solubilising agent .
3.1.2. Collection of the particulate phase
Diesel particulate matter (PM) is frequently defined from the material collected on a filter at a temperature of 52°C (or less) after dilution of the diesel exhaust with air. Even if the experiments conducted inside a dilution tunnel do not represent the full range of atmospheric conditions, these sampling conditions are far more common.
With regard to determining particulate PAHs in atmospheric aerosols, many different types of filters can be used and compared for retaining them; filters made of quartz, glass fibres, Teflon coated and nylon can be used . For diesel exhaust, collection systems are also generally composed of glass fibre filters to trap the particulate matter,
The sampling procedure using filters to collect particle bound PAHs provides no information about the size of the particulate matter; therefore, a high-flow cascade impactor can be used to replace single filters, which collects particles based on size . Many cascade impactors can separate the particulate matter using different quartz filters placed in each stages into eight size ranges, from particles smaller than 0.4 µm to sizes in the range of 6.6-10.5 µm . Aluminium filters that have silicon grease sprayed onto their surfaces can also be used in each stage of the impactors to prevent the bouncing of the particles during the collection; therefore, the distribution of PAHs based on the particulate sizes can be evaluated .
Finally, many studies have focused on particles directly collected inside of a diesel particulate filter (DPF) to understand the effects that an exhaust after-treatment device may have on the formation of particle-bound PAHs; once the DPF filter is weighed for total mass emission control, the particles can be blown-off and recovered for subsequent chemical analysis .
3.2. Extraction of PAHs from the trapping media
3.2.1. Extraction and purification of trapped gaseous PAHs
Vapour-phase PAHs and nitro-PAHs present in the trapped phase are often solvent-extracted using conventional techniques such as an ultrasonic bath or Soxhlet apparatus. A large number of polyurethane foams are Soxhlet extracted with 10% diethyl ether in hexane, as described in US EPA method TO-13.
XAD-2 resins are also often Soxhlet extracted over the course of 8 hours with 120 mL of methylene chloride , whereas mixtures of PAHs and nitro-PAHs can be better extracted from XAD-16 resins using 300 mL of methylene chloride:acetonitrile 3:1 (v:v) for 16 hours ; the extracts are then concentrated to 1-2 mL using rotary evaporators or under nitrogen flow, and they must be purified before analysis to eliminate matrix interferences. For the cleanup process, the concentrated solutions can be introduced into a silica column that contains anhydrous sodium sulphate to exclude water, and then eluted with 20 mL of methylene chloride:hexane 1:2 (to recover PAHs) and 30 mL of acetone:hexane 1:2 (to better recover nitro-PAHs). Finally, after purification, another concentration step by evaporation is necessary to enhance the concentration of solutes to be analysed. Each of these steps (desorption, evaporation, purification, and evaporation) is time consuming, and large volumes of organic solvents are consumed; additionally, the evaporation concentration steps can be critical for obtaining quantitative results for the most volatile PAHs.
Another method for concentrating and cleaning PAHs (in one step) after their absorption in an aqueous medium is the use of a solid phase extraction process (SPE), which consists of percolating the PAHs solubilising aqueous medium through a short column containing hydrophobic packing material and eluting them directly inside of the analytical apparatus without any losses. This method is less time and solvent consuming .
3.2.2. Extraction of PAHs from diesel particles
Among all of the solid environmental polluted matrices studied, such as soils, sediments or urban dusts, carbonaceous diesel particulate matter is known to require severe conditions to obtain good recovery yields of the higher molecular weight PAHs . It was even suggested that among all of the natural environmental matrices, diesel PM was the most refractory . Despite this observation, only a few studies have a reliable optimisation of the PAHs extraction step from the carbonaceous matrix.
188.8.131.52. Conventional solvent extraction methods
In a significant number of studies, PAHs are extracted from PM trapped in glass-fibre filters in ultrasonic baths; for example, Karavakalis
Soxhlet extraction can be enhanced with hot Soxhlet, where heating is also applied to the extraction cavity (unlike conventional Soxhlet), but the temperature must be kept lower than the boiling point of the extracting solvent mixture to keep it in the liquid state; therefore, temperatures are not high, and even if the recoveries are slightly better than using conventional Soxhlet, it remains difficult to quantitatively extract high weight PAHs from poor SOF diesel particles .
Finally, before the analytical step, columns containing a mixture of silica gel and deactivated alumina can be used for the fractionation and purification of extracts; the elution with
184.108.40.206. Recent rapid solvent extraction methods
Other extraction procedures, such as microwave-assisted extraction (MAE), supercritical fluid extraction (SFE) or assisted solvent extraction (ASE) can favourably replace Soxhlet or sonication extractions and yields cleaner extracts with minimal loss of volatile compounds and minimal use of solvents. Although these recent and more effective extraction methods are employed to extract PAHs or nitro-PAHs from solid matrices such as soils, sediments, plants or atmospheric dusts [66-70], they are only little used for the extraction of PAHs from collected diesel soot.
Microwave-assisted extraction uses closed inert vessels that contain the solid matrix and the organic solvents subjected to microwave irradiation (see Figure 2a). An important advantage of the MAE technique is the extraction rate acceleration due to microwave irradiation, resulting in an immediate heating to 120-140°C; therefore, extraction times on the order of a few minutes (approximately 30 minutes) can be obtained compared to a few hours when Soxhlet is used. Solvent volumes are low and range between 15 and 40 mL, depending on the quantity of matrix to be extracted. The solvent mixtures may have a dielectrical constant that is large enough to permit the heating transfer, and typical solvents such as acetonitrile or mixtures of toluene:acetone are employed to extract PAHs from atmospheric particles [71, 72]. In fact, the choice of the nature and the volume of the extracting solvents is especially important for the quantitative extraction of PAHs from diesel particles. Additionally, in the case of diesel soot with a very little SOF fraction, mixtures of drastic solvents such as pyridine:diethylamine or pyridine:acetic acid must be employed to quantitatively extract high weight PAHs or nitro-PAHs .
Supercritical fluid extraction exploits the unique properties of a supercritical fluid to more rapidly extract organic analytes from solid matrices, because the supercritical state imparts a great diffusion rate (like in the gaseous state) and a good solvating power (like in the liquid state). Carbon dioxide is the most used supercritical fluid because its critical temperature of 31°C and critical pressure of 74 bar are easily obtained. Supercritical fluids offer the opportunity to control the solvating power of the extraction fluid by varying the temperature (50 to 150 °C) and the pressure (100 to 400 bars), but also by adding minimal organic modifier (Figure 2b). In fact, the addition of small amounts of cosolvent into the CO2 is absolutely necessary, not only to increase the PAH solubility in the extractant fluid but also to break the strong interactions between the aromatic retention sites of soot surface and the PAHs and nitro-PAHs: cosolvent mixtures of methylene chloride and toluene can be added to better extract PAHs from diesel soot , but other less conventional cosolvent mixtures, containing pyridine, are sometimes required . SFE is an attractive method, as it leads to rapid extractions (less than 45 minutes, combining static and dynamic steps) and generates extracts ready for analysis without the need for additional concentration by means of solvent evaporation, because the extracted solutes are recovered into a very small volume of solvent. Moreover, SFE provides clean extracts because of its higher selectivity when compared to liquid solvent extraction techniques. Consequently, time consuming clean-up steps, which are also a source of analytical error, are not absolutely necessary after SFE extractions .
More recently, a method named accelerated solvent extraction (ASE) or pressurised fluid extraction (PFE) was developed. This method uses an organic solvent at a relatively high pressure and temperature to achieve more rapid extractions from solid matrices (Figure 2c) . Elevated temperatures (150-200°C) permit to disrupt the strong solute-matrix interactions, and a high pressure (100-150 bars) forces the extraction solvent into the matrix pores. Less than 20 mL of solvent can be used to extract PAHs and nitro-PAHs from diesel PM; extractions with toluene , methylene chloride  or less conventional solvents based on pyridine  were performed.
Finally, we stress the importance of optimising the PAH extraction step from soot; a chemometric approach can be useful because the influence of several operating variables must be understood. Indeed, the use of an experimental design fully permits the evaluation of not only the effects of each variable but also the interaction effects between the studied parameters, and at last permits the construction of a mathematical model that relates the observed response (PAH recovery yields in %) to the various factors and to their combinations (Figure 3).
220.127.116.11. Extractions without solvent
To avoid the use of organic solvents, other extraction techniques for chemical substances from particulate matter are proposed. Solid phase micro-extraction (SPME) seems to provide an alternative to solvent extraction methods . Head-space SPME methods using polydimethylsiloxane fibres were tested on certified diesel particulate matter; it consisted in equilibrating PAHs sorbed on PM between a saline aqueous phase and the SPME fibre, and then the fibre was thermally desorbed inside the injection port of a gas chromatographer. However, this method was acceptable only for two to four PAHs congeners and was long (4 hours) . Another method is to thermally desorb PAHs from filters or PM at 550°C in a thermogravimetric analyser, then recover them in a sampling bag where the vaporised phase is in equilibrium with a SPME fibre. Thereafter, PAHs are desorbed from the SPME fibre into a gas chromatographer . However, for the quantitative analysis of high weight PAHs,the time necessary to establish the equilibrium (especially at higher concentration levels) is very long and can exceed 15h.
Direct thermal desorption (TD) can also be used for the desorption of PAHs from PM and this technique is generally hyphenated to a gas chromatographer for subsequent analysis. However, this fast extraction technique, which overcomes the main drawbacks of solvent extractions, is more often performed for PAHs sorbed on airborne particulate matter [81-83]; therefore, PAHs are desorbed from air dusts at 300-340°C (without pyrolytic degradation), cryogenically trapped and afterwards released in the gas chromatographer injection port at 325-400°C with a helium flow. Thermal desorption of PAHs from diesel exhaust particles seems to be more difficult and less reproducible, especially for high molecular weight PAHs .
Laser desorption-ionisation has also been studied to characterise pollutants immobilised on solid particles, and it offers the advantages of being orders of magnitude more sensitive for the analysis of PAHs and more rapid than solvent extraction. As will be discussed later, laser desorption systems are directly hyphenated to mass spectrometer analysers. Particulate PAHs and nitro-PAHs sorbed on soot particles are generally desorbed at an ionisation wavelength of 193 nm or 266 nm by an UV laser, mixed to a nebulised aerosol and transferred to the ion source region of the mass spectrometer ; solid samples to be desorbed can also be directly introduced with a probe into the ion source chamber [86, 87]. It has been described that this energetic UV laser desorption technology is vulnerable to matrix effects, and absolute quantification of PAHs seems to be difficult . Therefore, new methods have appeared where particulate PAHs are deposited onto a probe, are irradiated with a less energetic pulsed Infra-Red laser beam (1064 nm) and the vaporised molecules are photoionised with UV radiation at 118 nm, so fragmentations are minimised and the sensitivity is higher .
3.3. Identification and quantitation of PAHs and their derivatives
3.3.1. On-line mass spectrometry analysis
To avoid time consuming sample preparation, we previously mentioned that PAHs can be desorbed from soot particles by IR or UV lasers, and after an ionisation step, they can be directly analysed by mass spectrometry. Generally, time-of-flight (TOF) mass spectrometers are used, and mass peaks ranging from 1 to 5000 g mol-1 are displayed. The advantages of this on-line analysis are that very small amounts of PM are required (as small as 10-12 to 10-11 g) and that the mass range is virtually unlimited . Moreover, even if multiple mass spectra are required to yield a representative spectrum for each chemical species present in the particulate effluent, high acquisition rates allow a significant increase in time resolution and measurements can be performed within minutes . The drawbacks are that only qualitative analyses are assured (identification of compound classes), due to effects of species variations in the small irradiated sample area and to the variability of the laser intensity . Moreover, there is not any selectivity on PAHs isomers on mass spectra, and interferences due to alkylated compounds, carbon clusters, polyynes compounds and photofragments of nitro-PAHs are inevitable in spectra because of the complexity of diesel soot particles. On-line carbon speciation of diesel exhaust particles can also be performed by near-edge X-ray absorption spectroscopy (NEXAFS), but the same drawbacks can be underlined: only fingerprints can be established because PAHs isomers cannot be resolved and quantitative information cannot be proposed . Consequently, a separation technique before the detection instrument seems essential to obtain isomer resolution and quantitation.
3.3.2. Chromatographic analysis
18.104.22.168. Gas chromatography (GC)
The vast majority of chromatographic separations of PAHs and nitro-PAHs in gas chromatography were obtained using classical columns with a length of 30 m, and an internal diameter of 0.25 mm; the open tube is generally coated with a stationary phase composed of cross-linked phenyl (5%) methyl (95%) siloxane (film thickness of 0.25 µm). However, many researchers have used a less polar stationary phase for the separation of PAHs (100% methyl), and a more polar one for nitro-PAHs (50% phenyl) . Original stationary phases sometimes have to be employed to obtain an isomer resolution of non-priority high weight PAHs, which are nevertheless of considerable interest because they have a high carcinogenicity; smectic-liquid crystalline polysiloxane phases permitted the separation of these PAHs . Another method for a better isomer resolution was to use a longer column, which was 50-60 m long . The most used detector for detecting PAHs or nitro-PAHs after their chromatographic separation is the mass spectrometer, which has the advantages of being more sensitive and providing information for identification, compared to the flame ionisation detector . Quadrupole mass analysers are the most used for PAHs detection, with electron ionization energies of 70 eV. Ion traps can also be used, which provide more accurate structural information (for isomer identification) in the MS-MS mode . With regard to nitro-PAHs, the electron-capture detector (ECD) can be employed, which is a sensitive and selective detector . MS detectors can also be used for the detection of nitro-PAHs, but with different ionisation modes than those applied for PAHs; the most frequent mode is negative chemical ionisation (NICI) with methane as a reagent gas , but electron monochromator mass spectrometry (EM-MS) appears to be more selective and specific .
It must be noted that the use of programmable temperature vaporisation (PTV) injection systems may enhance the sensitivity by injecting up to 40 µL of samples instead of the 1 µL used for classical split-splitless injectors . However, GC injection systems can also be directly hyphenated to thermodesorption units, which permits on-line PAH thermodesorption, GC separation and MS detection , as mentioned in a previous chapter. Finally, it will be necessary to count on comprehensive two dimensional GC techniques (GCxGC) in the future to obtain increased separation power and better sensitivity .
22.214.171.124. High performance liquid chromatography (HPLC)
As PAHs are lipophilic compounds, separations are generally achieved using reversed phase liquid chromatography with an apolar octadecyl (C18) column and a mobile phase composed of acetonitrile and water. However, phenyl-modified stationary phases can also be employed for the separation of PAHs and their oxidised derivatives, with methanol and water used as a mobile phase . Even if Ultra-Violet detectors can be used to detect PAHs and nitroPAHs , fluorescence detectors are more frequently employed for PAHs because of their greater sensitivity and selectivity, even if one of the sixteen priority PAHs cannot be detected (acenaphtylene) . Nitro-PAHs must be derivatised to be fluorescent (reduction to the amine), and other more appropriate detectors can be employed for their detection, such as chemiluminescence or coulometric detectors . Mass spectrometers have also proven to be useful detectors; PAHs can be analysed using an atmospheric pressure chemical ionisation interface (APCI) between the separation column and a single-quadrupole detection system ; atmospheric pressure photoionisation interfaces (APPI) can also be coupled to triple quadrupole mass spectrometers, permitting the analysis of PAHs in the positive ion mode, and nitro-PAHs in the negative ion mode, but also providing structural information about the metabolites . Analytical systems were developed to improve the sensitivity of nitro-PAHs analysis (over chemiluminescence detection) using a two dimensional HPLC procedure (on-line derivatisation and separation), an electrospray ionisation source (ESI) and a triple quadrupole mass spectrometer . Finally, a highly original approach consisting of a hyphenated HPLC and GC-MS resulted in the better analysis of isomers of high weight PAHs from diesel particulate matter .
It is a known fact that polyaromatic hydrocarbons in diesel exhaust are harmful. Therefore, it seems crucial to characterise them in both the gaseous and particulate phases, even if they are not yet regulated pollutants. It has been shown here that a variety of measurement protocols are available and that, even if many regulations in diesel exhaust sampling exist, it is not the case for the whole analytical process. And even for the first step of the measurement, the dilution factor and sampling temperature range are not strictly specified, which can induce great variability in diesel particle mass and composition. For that reason, various conclusions have been drawn about the influence of fuel composition, after-treatment devices, engine load, etc., on PAHs emissions; however, results from different research groups remain difficult to compare and all of the analytical artefacts were not resolved. For example, differentiating between gaseous and particle-bound PAHs is still a problem, because of the desorption or re-adsorption of volatile compounds during sampling. Additionally, neglecting the vapour-phase analysis (as suggested in some studies) also introduces significant error, because the toxic equivalent factors of exhaust are not correctly evaluated. The second step of the analytical process is also, without a doubt, an important source of analytical bias. There is not a universal technique for the extraction of every possible PAH or nitro-PAH from a solid matrix, and all of the described techniques have advantages and disadvantages; for example, high time resolution when coupling the laser desorption directly with the detection is not compatible with isomeric resolution, and thermal desorption remains less reproducible than solvent extraction. With regard to solvent extraction, which is the most employed method for the extraction of PAHs and nitro-PAHs from diesel soot, its optimisation is regrettably widely neglected. Conventional extraction methods such as Soxhlet or ultrasonic extractions, which are generally investigated on diesel PM extractions, and conventional solvents, such as methylene chloride or hexane, are in many cases not sufficient to quantitatively extract high weight PAHs and nitro-PAHs from carbonaceous diesel PM . It is particularly the case for “dry” diesel soot, which has a reduced portion of soluble organic fraction. Indeed, in this case, the sorption is dominated by strong surface adsorption while a high amount of SOF attenuates PAHs adsorption, blocking the energetic sites, and thus a simple phase partitioning dominates . Consequently, the presence on the particles of relevant amounts of SOF helps the solvent extraction process; however, it is now relevant to notice that recent diesel engines that are equipped with oxidation catalysts and particulate filters produce leaner particulates, and as it previously mentioned, more drastic extraction conditions are required . Therefore, in the future, it will be important to pay more attention on the optimisation of the extraction step to obtain quantitative results, especially for the highest weight and more toxic PAHs and nitro-PAHs. Then, new standard reference materials with low SOF, issued from more recent diesel engines, should be produced, characterised and commercialised to validate this important analytical step. Finally, it can be emphasised that studies on PAHs other than the sixteen priority ones, as well as on other oxygenated or sulphured derivatives, could be another important task in the future, considering the fact that some of them are particularly more dangerous. For those studies, comprehensive chromatographic techniques (GCxGC) could help in enhancing the resolution of hundreds of aromatic compounds that can be found on diesel particles.
Abbreviations and symbols
APCI Atmospheric Pressure Chemical ionisation
APPI Atmospheric Pressure PhotoIonisation
ASE Assisted Solvent Extraction
CVS Constant Volume Sampling
DPF Diesel Particulate Filter
ECD Electron Capture Detector
EM-MS Electron Monochromator Mass Spectrometry
ESI Electro Spray Ionisation
GC Gas Chromatography
HPLC High Pressure Liquid Chromatography
IARC International Agency for Research on Cancer Classification
KHHenry's law constant
MAE Microwave Assisted Extraction
MS Mass Spectrometry
NEDC New European Driving Cycle
NEXAFS Near Edge Xray Absorption Spectroscopy
NICI Negative Chemical Ionisation
PAH/PAHs Polycyclic Aromatic Hydrocarbon(s)
PM Particulate Matter
PTV Programmable Temperature Vaporisation
PUF PolyUrethane Foam
SFE Supercritical Fluid Extraction
SOF Soluble Organic Fraction
SPE Solid Phase Extraction
SPME Solid Phase Micro Extraction
TD Thermal Desorption
TOF Time of Flight
US-EPAUnited States Environmental Protection Agency
UV Ultra Violet
WHO World Health Organization
XAD/XAD-2/XAD-16 Resins with different macroreticular porosity
Li Q Wyatt A Kamens R. M 2009Oxidant generation and toxicity enhancement of aged-diesel exhaust. Atmospheric Environment. 43 1037 1042
toxicity, and source apportionment of polycylic aromatic hydrocarbons (PAHs) in road dust of Ulsan, Korea. Chemosphere. T. T. T Lee B. -K 2009 Characteristics 74 1245 1253
Andersson H Piras E Demma J Hellman B Brittebo E 2009Low levels of the air pollutant 1-nitropyrene induce DNA damage, increased levels of reactive oxygen species and endoplasmic reticulum stress in human endothelial cells. Toxicology. 262 57 64
Okuda T Okamoto K Tanaka S Shen Z Han Y Huo Z 2010Measurement and source identification of polycyclic aromatic hydrocarbons (PAHs) in the aerosol in Xi’an, China, by using automated column chromatography and applying positive matrix factorization (PMF). Science of The Total Environment. 408 1909 1914
Duran A Carmona M Monteagudo J 2004Modelling soot and SOF emissions from a diesel engine. Chemosphere. 56 209 225
Tan P Hu Z Deng K Lu J Lou D Wan G 2007Particulate matter emission modelling based on soot and SOF from direct injection diesel engines. Energy Conversion and Management. 48 510 518
Kittelson D Watts W Johnson J Schauer J Lawson D 2006On-road and laboratory evaluation of combustion aerosols-Part 2: Summary of spark ignition engine results. Journal of Aerosol Science. 37 931 949
IARC ( 2010IARC monographs on the evaluation of carcinogenic risks to humans 92Some non-heterocyclic polycyclic aromatic hydrocarbons and some related exposures.
Environmental Health Criteria EHC n°229 (First draft prepared by Kielhorn J, Wahnschaffe U, Mangelsdorf U. Fraunhofer Institute of Toxicology and Aerosol Research, Hanover, Germany. 2003Selected nitro- and nitro oxy-polycyclic aromatic hydrocarbons
EFSA (The EFSA Journal 2008Scientific Opinion of the Panel on Contaminants in the Food Chain on a request from the European Commission on Polycyclic Aromatic Hydrocarbons in Food 724 1 114
Third International Symposium on Chemistry and BiologyMichigan ( 1979Polynuclear aromatic hydrocarbons, in: Jones P., Leber P. (Eds.), Third International Symposium on Chemistry and Biology: carcinogenesis and mutagenesis, Ann Arbor Science.
North Carolina, USA ( U. S Epa 1990United States Environmental Protection Agency, Cancer risk from outdoor exposure to air toxics, 1Final Report.
IARC (list of IARC Evaluations, polynuclear aromatic hydrocarbons (PAH, Air quality guidelines for Europe). Copenhagen, WHO Regional Office for Europe, 1998International Agency for Research on Cancer 105 117
Busby Jr. W.F, Lafleur A.L, Penman B.W, Crespi C.L ( Durant J. L 1996Human cell mutagenicity of oxygenated, nitrated and unsubstituted polycyclic aromatic hydrocarbons associated with urban aerosols. Mutation Research. 371 3 4
Alessandria., Gilli G ( Traversi D Schiliro T Degan R Pignata C 2011Involvement of nitro-compounds in the mutagenicity of urban PM2.5 and PM10 in Turin. Mutation Research. 726 54 59
Bamford H. A Bezabeh D. Z Schantz M. M Wise S. A Baker J. E 2003Determination and comparison of nitrated- polycyclic aromatic hydrocarbons measured in air and diesel particulate reference materials, Chemosphere. 50 575 587
Yang X Igarashi K Tang N Lin J. M Wang W Kameda T Toriba A Hayakawa K 2010Indirect- and direct-acting mutagenicity of diesel, coal and wood burning-derived particulates and contribution of polycyclic aromatic hydrocarbons and nitro-polycyclic aromatic hydrocarbons. Mutation Research. 695 29 34
Toriba., Kizu R, Hayakawa K ( Taga R Tang N Hattori T Tamura K Sakaic S 2005Direct-acting mutagenicity of extracts of coal burning-derived particulates and contribution of nitro-polycyclic aromatic hydrocarbons. Mutation Research. 581 91 95
Maricq M. M 2007Chemical characterization of particulate emissions from diesel engines: a review. Aerosol Science. 38 1079 1118
Chang C-T Chen B-Y 2008Toxicity assessment of volatile organic compounds and polycyclic aromatic hydrocarbons in motorcycle exhaust. Journal of Hazardous Materials. 153 1262 1269
Chiang H-L Lai Y-M Chang S-Y 2012Pollutant constituents of exhaust emitted from light-duty diesel vehicles. Atmospheric Environment. 47 399 406
Turrio-baldassarri L Battistelli C. L Conti L Crebelli R De Berardis B Iamiceli A. L Gambino M Iannaccone S 2004Emission comparison of urban bus engine fueled with diesel oil and ‘biodiesel’ blend. Science of the Total Environment. 327 147 162
Bergvall C Westerholm R 2009Determination of highly carcinogenic dibenzopyrene isomers in particulate emissions from two diesel and two gasoline-fuelled light-duty vehicles. Atmospheric Environment. 43 3883 3890
Ravindra K Ranjeet S Van Grieken R 2008Review: Atmospheric polycyclic aromatic hydrocarbons: source attribution,emissions factors and regulation. Atmospheric Environment. 42 2895 2921
Mostert M. M. R Ayoko G. A Kokot S 2010Application of chemometrics to analysis of soil pollutants. Trends in Analytical Chemistry. 29 430 435
Tobiszewski M Namiesnik J 2012Review: PAH diagnostic ratios for the identification of pollution emission Sources. Environmental Pollution. 162 110 119
Zhang X. L Tao S Liu W. X Yang Y Zuo Q Liu S. Z 2005Source diagnostics of polycyclic aromatic hydrocarbons based on species ratios: a multimedia approach. Environmental Science and Technology. 39 9109 9114
Ravindra K Wauters E Van Grieken R 2008Variation in particulate PAHs levels and their relation with the trans-boundary movement of the air masses. Science of the Total Environment. 396 100 110
Pies C Hoffmann B Petrowsky J Yang Y Ternes T. A Hofmann T 2008Characterization and source identification of polycyclic aromatic hydrocarbons (PAHs) in river bank soils. Chemosphere. 72 1594 1601
De La Torre-roche R. J Lee W-Y Campos-díaz S. I 2009Soil-borne polycyclic aromatic hydrocarbons in El Paso, Texas: analysis of a potential problem in the United States/Mexico border region. Journal of Hazardous Materials. 163 946 958
Akyüz M Çabuk H 2010Gas particle partitioning and seasonal variation of polycyclic aromatic hydrocarbons in the atmosphere of Zonguldak, Turkey. Science of the Total Environment. 408 5550 5558
Yunker M. B Macdonald R. W Vingarzan R Mitchell R. H Goyette D Sylvestre S 2002PAHs in the Fraser River basin: a critical appraisal of PAH ratios as indicators of PAH source and composition. Organic Geochemistry. 33 489 515
Oliveira C Martins N Tavares J Pio C Cerqueira M Matos M Silva H Oliveira C Camoes F 2011Size distribution of polycyclic aromatic hydrocarbons in a roadway tunnel in Lisbon, Portugal. Chemosphere. 83 1588 1596
Opuene K Agbozu I. E Adegboro O. O 2009A critical appraisal of PAH indices as indicators of PAH source and composition in Elelenwo Creek, southern Nigeria. Environmentalist. 29 47 55
Callén M. S De La Cruz M. T López J. M Mastral A. M 2011PAH in airborne particulate matter. Carcinogenic character of PM10 samples and assessment of the energy generation impact. Fuel Processing and. 92 176 182
Katsoyiannis A Terzi E Cai Q-Y 2007On the use of PAH molecular diagnostic ratios in sewage sludge for the understanding of the PAH sources. Is this use appropriate? Chemosphere. 69 1337 1339
Galarneau E 2008Source specificity and atmospheric processing of airborne PAHs: implications for source apportionment. Atmospheric Environment. 42 8139 8149
Zhang W Zhang S Wan C Yue D Ye Y Wang X 2008Source diagnostics of polycyclic aromatic hydrocarbons in urban road runoff, dust, rain and canopy through fall. Environmental Pollution. 153 594 601
Saarnio K Sillanpää M Hillamo R Sandell E Pennanen A. R Solanen R. O 2008Polycyclic aromatic hydrocarbons in size-segregated particular matter from six urban sites in Europe. Atmospheric Environment. 42 9087 9097
Karavalakis G Fontaras G Ampatzoglou D Kousoulidou M Stournas S Samaras Z Bakeas E 2010Effects of low concentration biodiesel blends application on modern passenger cars. Part 3: Impact on PAH, nitro PAH and oxy-PAH emissions. Environmental Pollution. 158 1584 1594
Mari M Harrison R. M Schuhmacher M Domingo J. L Pongpiachan S 2010Interferences over the sources and processes affecting polycyclic aromatic hydrocarbons in the atmosphere derived from measured data. Science of the Total Environment. 408 2387 2393
Magara-gomez K Olson M. R Okuda T Walz K. A 2012Sensitivity of hazardous air pollutant emissions to the combustion of blends of petroleum diesel and biodiesel fuel. Atmospheric Environment. 50 307 313
Burtscher H 2005Physical characterization of particulate emissions from diesel engines: a review. Aerosol Science. 36 896 932
Bukowiecki N Kittelson D Watts W Burtscher H Weingartner E Baltensperger U 2002Real-time characterization of ultrafine and accumulation mode particles in ambient combustion aerosols. Journal of Aerosol Science. 33 1139 1154
Karavalakis G Bakeas E Fontaras G Stournas S 2011Effect of biodiesel origin on regulated and particle-bound PAH (polycyclic aromatic hydrocarbon) emissions from a Euro 4 passenger car. Energy. 36 5328 5337
Pakbin P Ning Z Schauer J. J Sioutas C 2009Characterization of Particle Bound Organic Carbon from Diesel Vehicles Equipped with Advanced Emission Control Technologies. Environmental Science & Technology. 43 4679 4686
Liu Z. G Berg D. R Swor T. A Schauer J. J 2008Comparative Analysis on the Effects of Diesel Particulate Filter and Selective Catalytic Reduction Systems on a Wide Spectrum of Chemical Species Emissions. Environmental Science & Technology. 42 6080 6085
He C Ge Y Tan J You K Han X Wang J 2010Characteristics of polycyclic aromatic hydrocarbons emissions of diesel engine fueled with biodiesel and diesel. Fuel. 89 2040 2046
Liou Y-J; Cheng M-T, Lu J-H, Yang H-H, Tsai Y.I, Wang L-C, Chen C-B, Lai J-S ( Young L-H 2012Effects of biodiesel, engine load and diesel particulate filter on nonvolatile particle number size distributions in heavy-duty diesel engine exhaust. Journal of Hazardous Materials. 200 282 289
Heeb N. V Schmid P Kohler M Gujer E Zennegg M Wenger D Wichser A Ulrich A Gfeller U Honegger P Zeyer K Emmenegger L Petermann J-L Czerwinski J Mosimann T Kasper M Mayer A 2008Secondary Effects of Catalytic Diesel Particulate Filters: Conversion of PAHs versus Formation of Nitro-PAHs. Environmental Science & Technology. 42 3773 3779
Dimashki M Harrad S Harrison R. M 2000Measurements of nitro-PAH in the atmospheres of two cities. Atmospheric Environment. 34 2459 2469
Esen F Tasdemir Y Vardar N 2008Atmospheric concentrations of PAHs, their possible sources and gas-to-particle partitioning at a residential site of Bursa, Turkey. Atmospheric Research. 88 243 255
De Abrantes R De Assunçao J. V Pesquero C. R 2004Emission of polycyclic aromatic hydrocarbons from light-duty diesel vehicles exhaust. Atmos. Environ. 38 1631 1640
Yang H-H Hsieh L-T Liu H-C Mi H-H 2005Polycyclic aromatic hydrocarbon emissions from motorcycles. Atmospheric Environment. 39 17 25
Zielinska B Sagebiel J Arnott W. P Rogers C. F Kelly K. E Wagner D. A Lighty J. S Sarofim A. F Palmer G 2004Phase and Size Distribution of Polycyclic Aromatic Hydrocarbons in Diesel and Gasoline Vehicle Emissions. Environmental Science & Technology. 38 2557 2567
Portet-koltalo F Preterre D Dionnet F 2011A new analytical methodology for a fast evaluation of semi-volatile polycyclic aromatic hydrocarbons in the vapor phase downstream of a diesel engine particulate filter. Journal of Chromatography A. 1218 981 989
Borras E Tortajada-genaro L. A 2007Characterization of polycyclic aromatic hydrocarbons in atmospheric aerosols by gas-chromatography-mass spectrometry. Analytica Chimica Acta. 583 266 276
Song W. W He K. B Wang J. X Wang X. T Shi X. Y Yu C Chen W. M Zheng L 2011Emissions of EC, OC, and PAHs from Cottonseed Oil Biodiesel in a Heavy-Duty Diesel Engine. Environmental Science & Technology. 45 6683 6689
Lin Y-C Tsai C-H Yang C-R Wu C. J Wu T-Y Chang-chien G-P 2008Effects on aerosol size distribution of polycyclic aromatic hydrocarbons from the heavy-duty diesel generator fueled with feedstock palm-biodiesel blends. Atmospheric Environment. 42 6679 6688
Oukebdane K Portet-koltalo F Machour N Dionnet F Desbene P. L 2010Comparison of hot Soxhlet and accelerated solvent extractions with microwave and supercritical fluid extractions for the determination of polycyclic aromatic hydrocarbons and nitrated derivatives strongly adsorbed on soot collected inside a diesel particulate filter. Talanta. 82 227 236
Turrio-baldassarri L Battistelli C. L Iamiceli A. L 2003Evaluation of the efficiency of extraction of PAHs from diesel particulate matter with pressurized solvents. Analytical and Bioanalytical Chemistry. 375 589 595
Benner B. A 1998Summarizing the Effectiveness of Supercritical Fluid Extraction of Polycyclic Aromatic Hydrocarbons from Natural Matrix Environmental Samples. Analytical Chemistry. 70 4594 4601
Riddle S. G Jakober C. A Robert M. A Cahill T. M Charles M. J Kleeman M. J 2007Large PAHs detected in fine particulate matter emitted from light-duty gasoline vehicles. Atmospheric Environment. 41 8658 8668
Fernandes M. B Brooks P 2003Characterization of carbonaceous combustion residues: II. Nonpolar organic compounds. Chemosphere. 53 447 458
Rojas N. Y Milquez H. A Sarmiento H 2011Characterizing priority polycyclic aromatic hydrocarbons (PAH) in particulate matter from diesel and palm oil-based biodiesel B15 combustion. Atmospheric Environment. 45 6158 6162
Hawthorne S. B Grabanski C. B Martin E Miller D. J 2000Comparisons of Soxhlet extraction, pressurized liquid extraction, supercritical fluid extraction and subcritical water extraction for environmental solids: recovery, selectivity and effects on sample matrix. Journal of Chromatography A. 892 421 433
Luque de Castro M ( Priego-capote F Luque-garcia J 2003Automated fast extraction of nitrated polycyclic aromatic hydrocarbons from soil by focused microwave-assisted Soxhlet extraction prior to gas chromatography-electron-capture detection. Journal of Chromatography A. 994 159 167
Yusa V Quintas G Pardo O Pastor A Guardia M 2006Determination of PAHs in airborne particles by accelerated solvent extraction and large-volume injection-gas chromatography-mass spectrometry. Talanta. 69 807 815
Bruno P Caselli M De Gennaro G Tutino M 2007Determination of polycyclic aromatic hydrocarbons (PAHs) in particulate matter collected with low volume samplers. Talanta. 72 1357 1361
Itoh N Fushimi A Yarita T Aoyagi Y Numata M 2011Accurate quantification of polycyclic aromatic hydrocarbons in dust samples using microwave-assisted solvent extraction combined with isotope-dilution mass spectrometry. Analytica Chimica Acta. 699 49 56
Shu Y. Y Tey S. Y Wu D. K 2003Analysis of polycyclic aromatic hydrocarbons in airborne particles using open-vessel focused microwave-assisted extraction. Analytica Chimica Acta. 495 99 108
Castro D Slezakova K Delerue-matos C Alvim-ferraz M. C Morais S Pereira M. C 2011Polycyclic aromatic hydrocarbons in gas and particulate phases of indoor environments influenced by tobacco smoke: Levels, phase distributions, and health risks. Atmospheric Environment. 45 1799 1808
Portet-koltalo F Oukebdane K Dionnet F Desbene P. L 2008Optimisation of the extraction of polycyclic aromatic hydrocarbons and their nitrated derivatives from diesel particulate matter using microwave-assisted extraction. Analytical and Bioanalytical Chemistry. 390 389 398
Jones C Chughtai A Murugaverl B Smith D 2004Effects of air/fuel combustion ratio on the polycyclic aromatic hydrocarbon content of carbonaceous soots from selected fuels. Carbon. 42 2471 2484
Portet-koltalo F Oukebdane K Dionnet F Desbene P. L 2009Optimisation of supercritical fluid extraction of polycyclic aromatic hydrocarbons and their nitrated derivatives adsorbed on highly sorptive diesel particulate matter. Analytica Chimica Acta. 651 48 56
Bowadt S Hawthorne S. B 1995Supercritical fluid extraction in environmental analysis. Journal of Chromatography A. 703 549 571
Ryno M Rantanen L Papaioannou E Konstandopoulos A. G Koskentalo T Kavela K 2006Comparison of pressurized fluid extraction, Soxhlet extraction and sonication for the determination of polycyclic aromatic hydrocarbons in urban air and diesel exhaust particulate matter. Journal of Environmental Monitoring. 8 488 493
Tang B Isacsson U 2008Analysis of Mono- and Polycyclic Aromatic Hydrocarbons Using Solid-Phase Microextraction: State-of-the-Art. Energy & Fuels. 22 1425 1438
Vaz J. M 2003Screening direct analysis of PAHS in atmospheric particulate matter with SPME. Talanta. 60 687 693
Ballesteros R Hernandez J Lyons L 2009Determination of PAHs in diesel particulate matter using thermal extraction and solid phase micro-extraction. Atmospheric Environment. 43 655 662
Van Drooge B. L Nikolova I Ballesta P. P 2009Thermal desorption gas chromatography-mass spectrometry as an enhanced method for the quantification of polycyclic aromatic hydrocarbons from ambient air particulate matter. Journal of Chromatography A. 1216 4030 4039
Gil-molto J Varea M Galindo N Crespo J 2009Application of an automatic thermal desorption-gas chromatography-mass spectrometry system for the analysis of polycyclic aromatic hydrocarbons in airborne particulate matter. Journal of Chromatography A. 1216 1285 1289
Ancelet T Davy P. K Trompetter W. J Markwitz A Weatherburn D. C 2011Carbonaceous aerosols in an urban tunnel. Atmospheric Environment. 45 4463 4469
Lavrich R. J Hays M. D 2007Validation Studies of Thermal Extraction-GC/MS Applied to Source Emissions Aerosols. 1. Semivolatile Analyte- Nonvolatile Matrix Interactions. Analytical Chemistry. 79 3635 3645
Kalberer M Morrical B. D Sax M Zenobi R 2002Picogram Quantitation of Polycyclic Aromatic Hydrocarbons Adsorbed on Aerosol Particles by Two-Step Laser Mass Spectrometry. Analytical Chemistry. 74 3492 3497
Dotter R. N Smith C. H Young M. K Kelly P. B Jones A. D Mccauley E. M Chang D. P. Y 1996Laser Desorption/Ionization Time-of-Flight Mass Spectrometry of Nitrated Polycyclic Aromatic Hydrocarbons. Analytical Chemistry. 68 2319 2324
Dobbins R. A Fletcher R. A Benner B. A Hoeft S 2006Polycyclic aromatic hydrocarbons in flames, in diesel fuels, and in diesel emissions. Combustion and Flame. 144 773 781
Bente M Sklorz M Streibel T Zimmermann R 2008Online Laser Desorption-Multiphoton Postionization Mass Spectrometry of Individual Aerosol Particles: Molecular Source Indicators for Particles Emitted from Different Traffic-Related and Wood Combustion Sources. Analytical Chemistry. 80 8991 9004
Ferge T Muhlberger F Zimmermann R 2005Application of Infrared Laser Desorption Vacuum-UV Single-Photon Ionization Mass Spectrometry for Analysis of Organic Compounds from Particulate Matter Filter Samples. Analytical Chemistry. 77 4528 4538
Faccinetto A Desgroux P Ziskind M Therssen E Focsa C 2011High-sensitivity detection of polycyclic aromatic hydrocarbons adsorbed onto soot particles using laser desorption/laser ionization/time-of-flight mass spectrometry: An approach to studying the soot inception process in low-pressure flames. Combustion and Flame. 158 227 239
Braun A Mun B. S Huggins F. E Huffman G. P 2006Carbon Speciation of Diesel Exhaust and Urban Particulate Matter NIST Standard Reference Materials with C(1s) NEXAFS Spectroscopy. Environmental Science & Technology. 41 173 178
Kawanaka Y Sakamoto K Wang N Yun S-J 2007Simple and sensitive method for determination of nitrated polycyclic aromatic hydrocarbons in diesel exhaust particles by gas chromatography-negative ion chemical ionisation tandem mass spectrometry. Journal of Chromatography A. 1163 312 317
Schubert P Schantz M. M Sander L. C Wise S. A 2003Determination of Polycyclic Aromatic Hydrocarbons with Molecular Weight 300 and 302 in Environmental-Matrix Standard Reference Materials by Gas Chromatography/Mass Spectrometry. Analytical Chemistry. 75 234 246
Ratcliff M. A Dane A. J Williams A Ireland J Luecke J Mccormick R. L Voorhees K. J 2010Diesel Particle Filter and Fuel Effects on Heavy-Duty Diesel Engine Emissions. Environmental Science & Technology. 44 8343 8349
Bente M Sklorz M Streibel T Zimmermann R 2009Thermal Desorption-Multiphoton Ionization Time-of-Flight Mass Spectrometry of Individual Aerosol Particles: A Simplified Approach for Online Single-Particle Analysis of Polycyclic Aromatic Hydrocarbons and Their Derivatives. Analytical Chemistry. 81 2525 2536
Ozel M. Z Hamilton J. F Lewis A. C 2011New Sensitive and Quantitative Analysis Method for Organic Nitrogen Compounds in Urban Aerosol Samples. Environmental Science & Technology. 45 1497 1505
Letzel T Poschl U Wissiack R Rosenberg E Grasserbauer M Niessner R 2001Phenyl-Modified Reversed-Phase Liquid Chromatography Coupled to Atmospheric Pressure Chemical Ionization Mass Spectrometry: A Universal Method for the Analysis of Partially Oxidized Aromatic Hydrocarbons. Analytical Chemistry. 73 1634 1645
El Haddad I Marchand N Dron J Temime-roussel B Quivet E Wortham H Jaffrezo J. L Baduel C Voisin D Besombes J. L Gille G 2009Comprehensive primary particulate organic characterization of vehicular exhaust emissions in France. Atmospheric Environment. 43 6190 6198
Hutzler C Luch A Filser J. G 2011Analysis of carcinogenic polycyclic aromatic hydrocarbons in complex environmental mixtures by LC-APPI-MS/MS. Analytica Chimica Acta. 702 218 224
Miller-schulze J. P Paulsen M Toriba A Hayakawa K Simpson C. D 2007Analysis of 1-nitropyrene in air particulate matter standard reference materials by using two-dimensional high performance liquid chromatography with online reduction and tandem mass spectrometry detection. Journal of Chromatography A. 1167 154 160
Bergvall C Westerholm R 2008Determination of 252-302 Da and tentative identification of 316-376 Da polycyclic aromatic hydrocarbons in Standard Reference Materials 1649a Urban Dust and 1650b and 2975 Diesel Particulate Matter by accelerated solvent extraction-HPLC-GC-MS. Analytical and Bioanalytical Chemistry. 391 2235 2248
Jonker M. T. O Koelmans A. A 2002Extraction of Polycyclic Aromatic Hydrocarbons from Soot and Sediment: Solvent Evaluation and Implications for Sorption Mechanism. Environmental Science & Technology. 36 4107 4113
Endo S Grathwohl P Haderlein S. B Schmidt T. C 2009Effects of Native Organic Material and Water on Sorption Properties of Reference Diesel Soot. Environmental Science & Technology. 43 3187 3193