Application of single-particle laser desorption/ionization time-of-flight mass spectrometry for detection of polycyclic aromatic hydrocarbons from soot particles originating from an industrial combustion process

Detection of polycyclic aromatic hydrocarbons using a high performance-single particle aerosol mass spectrometer

The real-time detection of the mixing states of polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs in ambient particles is of great significance for analyzing the source, aging process, and health effects of PAHs and nitro-PAHs; yet there is still few effective technology to achieve this type of detection. In this study, 11 types of PAH and nitro-PAH standard samples were analyzed using a high performance-single particle aerosol mass spectrometer (HP-SPAMS) in lab studies. The identification principles 'parent ions' and 'mass-to-charge (m/z) = 77' of each compound were obtained in this study. It was found that different laser energies did not affect the identification of the parent ions. The comparative experiments of ambient atmospheric particles, cooking and biomass burning emitted particles with and without the addition of PAHs were conducted and ruled out the interferences from primary and secondary organics on the identification of PAHs. Besides, the reliability of the characteristic ions extraction method was evaluated through the comparative study of similarity algorithm and deep learning algorithm. In addition, the real PAH-containing particles from vehicle exhaust emissions and ambient particles were also analyzed. This study improves the ability of single particle mass spectrometry technology to detect PAHs and nitro-PAHs, and HP-SPAMS was superior to SPAMS for detecting single particles containing PAHs and nitro-PAHs. This study provides support for subsequent ambient observations to identify the characteristic spectrum of single particles containing PAHs and nitro-PAHs.

On-line fast analysis of light hydrocarbons, PAH and radicals by molecular-beam time of flight mass spectrometry

Volatile organic compounds (VOC) and polycyclic aromatic hydrocarbons (PAH), emitted in the environment from a wide range of combustion sources, are hazardous to human health and considered important precursors of both primary and secondary particulate pollutants. In the present work, light hydrocarbons up to C₉, as main components of combustion-derived VOC, and PAH produced in fuel-rich conditions of premixed ethylene flames were analyzed by implementing a molecular-beam time of flight mass spectrometer (MB-TOFMS), purposely built for on-line fast monitoring of the environmental impact of combustion systems. The reliability of the MB-TOFMS was preliminarily verified on a slightly-sooting flame, comparing the results with those obtained by batch sampling and gas chromatographic techniques. Electron ionization (EI) and multi-photon ionization (MPI) were used as MB-TOFMS sources and tested on combustion gases of a no-sooting premixed ethylene flame where VOC and PAH are present in traces not detectable with batch sampling and conventional analytical techniques. The mass identification accuracy was improved and guaranteed by systematically performing internal mass calibration, exploiting the formation of "in situ" clusters from combustion water in the molecular beam apparatus. Selective and sensitive monitoring of light hydrocarbons and PAH, derived from oxidation and pyrolysis reactions featuring combustion, was shown to be especially effective when using the MB-TOFMS equipped with MPI source. This technique showed to be effective also for the detection of radical species that are important for the risk assessment of aerosol and fundamental understanding of aerosol chemistry at a molecular level.

A really quick easy cheap effective rugged and safe (QuEChERS) extraction procedure for the analysis of particle-bound PAHs in ambient air and emission samples

A quick easy cheap effective rugged and safe (QuEChERS) like extraction procedure is presented for the measurement of polycyclic aromatic hydrocarbons (PAHs) associated to particulate matter from ambient air or combustion process. The procedure is based on a short mechanical agitation (vortex during 90 s) using a small volume of acetonitrile (7 ml) as extraction solvent. Equivalent extraction efficiencies were obtained when comparing the QuEChERS and the traditional pressurized solvent extraction (ASE) procedures for ambient air and emission (wood combustion) filter samples. The developed QuEChERS extraction protocol was validated with the analysis of a standard reference material (NIST SRM 1649a, urban dust). By comparison to other extraction methods including ASE, the simplicity of the QuEChERS protocol allows to minimize experimental errors, to decrease about a factor 5 the cost per extraction and to increase the productivity per working day by a 10-fold factor. This paper constitutes the first report on the applicability of a QuEChERS-like approach for the quantification of PAHs or other organic compounds in atmospheric particulate matter.

Rapid formation of secondary organic aerosol from the photolysis of 1-nitronaphthalene: role of naphthoxy radical self-reaction

The chemical composition of secondary organic aerosol (SOA) formed from the photolysis of 1-nitronaphthalene in a series of simulation chamber experiments has been investigated using an aerosol time-of-flight mass spectrometer (ATOFMS). The resulting SOA is characterized by the presence of a dimer (286 Da) proposed to be formed through the self-reaction of naphthoxy radicals along with the expected product nitronaphthol. The molecular formulas of the SOA products were confirmed by collecting filter samples and analyzing the extracts using ultrahigh resolution mass spectrometry. Further evidence for the radical self-reaction mechanism was obtained by photolyzing 1-nitronaphthalene in the presence of excess nitrobenzene, where it was shown that the resulting SOA contained a product consistent with the cross-reaction of phenoxy and naphthoxy radicals. The naphthoxy dimer was formed from the photolysis of 1-nitronaphthalene under a variety of different experimental conditions including the presence of excess butyl ether as an OH scavenger and the presence of ambient air and particles. However, formation of the dimer was suppressed when 1-nitronaphthalene was photolyzed in the presence of excess NO and nitronaphthol was instead found to be the dominant particle-phase product indicating that the yield of the dimer is dependent upon the concentration of pre-existing NO(x). The results of this work suggest that photolysis of 1-nitronaphthalene represents a previously unidentified pathway to SOA formation in the troposphere. Analogous mechanisms may also be important for other nitrated polycyclic aromatic hydrocarbons.

Quantitative high-resolution mapping of phenanthrene sorption to black carbon particles

Sorption of hydrophobic organic contaminants such as polycyclic aromatic hydrocarbons (PAHs) to black carbon (BC) particles has been the focus of numerous studies. Conclusions on sorption mechanisms of PAH on BC were mostly derived from studies of sorption isotherms and sorption kinetics, which are based on batch experiments. However, mechanistic modeling approaches consider processes at the subparticle scale, some including transport within the pore-space or different spatial pore-domains. Direct evidence based on analytical techniques operating at the submicrometer scale for the location of sorption sites and the adsorbed species is lacking. In this work, we identified, quantified, and mapped the sorption of PAHs on different BC particles (activated carbon, charcoal and diesel soot) on a 25-100 nm scale using scanning transmission X-ray microscopy (STXM). In addition, we visualized the pore structure of the particles by transmission electron microscopy (TEM) on the 1-10 nm-scale. The combination of the chemical information from STXM with the physical information from TEM revealed that phenanthrene accumulates in the interconnected pore-system along primary "cracks" in the particles, confirming an adsorption mechanism.

Instrumentation, data evaluation and quantification in on-line aerosol mass spectrometry

On-line micro- and nanoparticle mass spectrometry has evolved into a prominent analytical method for the characterization of airborne particles, particle populations and aerosols over the recent years, driven by essential developments in instrumentation, data evaluation and validation. In this tutorial, the fundamental aspects of the technology and methodology for qualitative and quantitative on-line aerosol particle analysis are discussed. Specific properties of the on-line mass spectrometric instrumentation for particle analysis are described, combined with a discussion of basic differences of the instruments and demands for future improvements of instruments and data analysis techniques. Optimized technology and methodology in particle analysis is expected to lead to essential growth of the knowledge and to quality improvement of the description of atmospheric processes and health effects in the future.

Fast determination of the relative elemental and organic carbon content of aerosol samples by on-line single-particle aerosol time-of-flight mass spectrometry

Different particulate matter (PM) samples were investigated by on-line single-particle aerosol time-of-flight mass spectrometry (ATOFMS). The samples consist of soot particulates made by a diffusion flame soot generator (combustion aerosol standard, CAST), industrially produced soot material (printex), soot from a diesel passenger car as well as ambient particulates (urban dust (NIST) and road tunnel dust). Five different CAST soot particle samples were generated with different elemental carbon (EC) and organic carbon (OC) content. The samples were reaerosolized and on-line analyzed by ATOFMS, as well as precipitated on quartz filters for conventional EC/OC analysis. For each sample ca. 1000 ATOFMS single-particle mass spectra were recorded and averaged. A typical averaged soot ATOFMS mass spectrum shows characteristic carbon cluster peak progressions (Cn+) as well as hydrogen-poor carbon cluster peaks (CnH(1-3)+). These peaks are originated predominately from the elemental carbon (EC) content of the particles. Often additional peaks, which are not due to carbon clusters, are observed, which either are originated from organic compounds (OC-organic carbon), or from the non-carbonaceous inorganic content of the particles. By classification of the mass spectral peaks as elemental carbon (i.e., the carbon cluster progression peaks) or as peaks originated from organic compounds (i.e., molecular and fragment ions), the relative abundance of elemental (EC) and organic carbon (OC) can be determined. The dimensionless TC/EC values, i.e., the ratio of total carbon content (TC, TC = OC + EC) to elemental carbon (EC), were derived from the ATOFMS single-particle aerosol mass spectrometry data. The EC/TC values measured by ATOFMS were compared with the TC/EC values determined by the thermal standard techniques (thermooptical and thermocoulometric method). A good agreement between the EC/TC values obtained by on-line ATOFMS and the offline standard method was found.

Application of Infrared Laser Desorption Vacuum-UV Single-Photon Ionization Mass Spectrometry for Analysis of Organic Compounds from Particulate Matter Filter Samples

A new built instrument suitable for laser desorption-single photon ionization time-of-flight mass spectrometry (LD-SPI-TOFMS) with use of Vacuum-UV photons with a wavelength of 118 nm was used for the analysis of organic compounds. Fragmentation-free analysis of a variety of substances was achieved for desorption experiments with pure compounds desorbed from quartz glass filters applying low desorption energies. It was further found that the rate of fragmentation is strongly dependent on the desorption energy. Matrix effects were investigated by desorption experiments utilizing soot spiked with several organic compounds.The characteristics of the desorption process are assessed in more detail and the impact on the analysis of ambient particulate matter (PM) samples on filters are discussed. First results obtained from the application of the technique to the analysis of organic compounds from ambient PM are presented. Furthermore, possibilities of future developments of the method, in particular for analysis of ambient PM, are discussed.

On-line analysis of gas-phase composition in the combustion chamber and particle emission characteristics during combustion of wood and waste in a small batch reactor

The emission of particulate matter and gaseous compounds during combustion of wood and refuse-derived fuel in a small batch reactor is investigated by laser mass-spectrometric on-line measurement techniques for gas-phase analysis and simultaneous registration of physical aerosol properties (number size distribution). The gas-phase composition is addressed by a laser-based mass spectrometric method, namely, vacuum-UV single-photon ionization time-of-flight mass spectrometry (VUV-SPI-TOFMS). Particle-size distributions are measured with a scanning mobility particle sizer. Furthermore, a photoelectric aerosol sensor is applied for detection of particle-bound polycyclic aromatic hydrocarbons. The different phases of wood combustion are distinguishable by both the chemical profiles of gas-phase components (e.g., polycyclic aromatic hydrocarbons, PAH) and the particle-size distribution. Furthermore, short disturbances of the combustion process due to air supply shortages are investigated regarding their effect on particle-size distribution and gas-phase composition, respectively. It is shown that the combustion conditions strongly influence the particle-size distribution as well as on the emission of particle-bound polycyclic aromatic hydrocarbons.

On-line analysis of the size distribution of fine and ultrafine aerosol particles in flue and stack gas of a municipal waste incineration plant: effects of dynamic process control measures and emission reduction devices

The size distribution of particles in the waste gas of a municipal waste incineration plant (23 MW) was measured on-line at two sampling points in the flue-gas duct (700 and 300 degrees C) as well as in the stack gas (80 degrees C). The measurements were performed during both stable combustion conditions and transient operating conditions. The particle measurements were carried out by a mobile system consisting of a home-designed sampling system with dilution device and a scanning mobility particle sizer (SMPS) for the particle size range 17-600 nm as well as an aerodynamic particle sizer (APS) for the size range 500 nm-30 microm. The APS and SMPS data were combined using a special method and a home written software tool. The maximum of the particle-size distribution in the flue gas of the incinerator shifts from about 90 nm at the 700 degrees C sampling point to about 140 nm at the 300 degrees C point, showing the particle growth by coagulation processes and condensation of inorganic and organic gaseous species with decreasing temperature. This finding is consistent with the measured concentration profiles of gaseous organic chemical species in the flue gas. While at flue-gas temperatures of 600-800 degrees C a rich pattern of polycyclic aromatic hydrocarbon species (PAH) is observable, the PAH concentrations are considerably reduced further downstream of the flue-gas channel, where the temperature drops below 500 degrees C. Condensation and reactive bonding of gaseous chemicals onto particulate matter is, among other reasons, responsible for the depletion of gas-phase species. Process control measures, such as firing the backup burners or cleaning of the grate with pressurized air, can cause dynamic changes of the particle-size distribution. Furthermore the flue-gas cleaning measures have great impact onto both the particle concentration and the size distribution. For this reason the impact of one particular emission reduction device, the wet electrostatic dust precipitator (wet-ESP), is evaluated. The wet-ESP reduces considerably the particle concentration over the whole size range. Behind the flue-gas processing units a broad maximum in the particle-size distribution occurs at about 70 nm, but no pronounced particle-size distribution could be observed. The particle concentration level atthis maximum is about 3 magnitudes lower than in the raw flue gas. However, intermittent periods lasting for several minutes of high emissions of ultrafine particles with d < 40 nm were observed. These particles are most likely formed by nucleation processes behind the wet-ESP from gas-phase constituents of the stack gas.