Composition and Morphology of Individual Combustion,Biomass Burning,and Secondary Organic Particle Types Obtained Using Urban and Coastal ATOFMS and STXM-NEXAFS Measurements

Complementary single particle measurements of organic aerosols using aerosol time-of-flight mass spectrometry (ATOFMS) and Scanning Transmission X-ray Microscopy—Near Edge X-ray Absorption Fine Structure (STXM-NEXAFS) are compared to examine the relationships between particle morphologies and chemical composition of particles having similar sources. ATOFMS measurements provide size-resolved chemical composition information for single particles. Measurements from field campaigns in polluted or urban (Riverside/SOAR 2005; Mexico City/MILAGRO 2006; Port of Long Beach 2007) and clean or marine (Arabian Sea/INDOEX 1999; Sea of Japan/ACE-Asia 2001; Trinidad Head/CIFEX 2004) locations illustrate regional differences. The majority (≥ 85 %) of the number of submicron particles are carbonaceous (including elemental and organic carbon), but represent less than 10% of the number of supermicron particles. Organic carbon (OC) particles are classified into three meta-classes corresponding to (1) combustion generated OC/EC internal mixtures, (2) biomass burning generated K/OC mixtures, and (3) OC/High Mass OC (HMOC) mixtures containing secondary markers of atmospheric processing. Normalized dot products are used to quantify similarity among fragment spectra and indicate that OC particle types are consistent across (and within) platforms. Single particle carbon STXM-NEXAFS measurements during ACE-Asia 2001 and MILAGRO 2006 yield similar source categories based on relative abundances of aromatic, alkane, and carboxylic acid functional groups. All three organic particle types correspond to a variety of very heterogeneous particle morphologies, although the highly oxygenated OC particles with likely secondary organic contributions frequently are nearly spherical, liquid-like particles. Size-resolved number fractions of the major ATOFMS OC particle types show qualitative agreement with OC particle types from STXM-NEXAFS analysis, indicating a correspondence of the OC/EC type with the presence of strong aromatic groups, of the OC/HMOC type with high carboxylic acid groups, and of the biomass burning OC type with aromatic and carbonyl groups. ATOFMS measurements can be used to establish robust statistics for offline single particle techniques, providing the atmospheric context for the functional group and morphological information obtained from STXM-NEXAFS for an improved understanding of the climate impact of organic aerosols.     

Single Particle Characterization of Automobile and Diesel Truck Emissions in the Caldecott Tunnel

Individual aerosol particles emitted from light-duty vehicles (LDV) and heavy-duty vehicles (HDV) were sampled in the Caldecott Tunnel (Berkeley, CA) using an aerosol time-of-flight mass spectrometer (ATOFMS). This instru ment determines both size and composition information of individual particles in real time. From the composition of individual particles, in conjunction with knowledge of the traffic patterns in the Caldecott Tunnel, information about the source of the particles can be determined. Based upon chemical composition, three main types of particles were detected: particles with significant mass spectral signal due to polycyclic aromatic hydrocarbons (PAH), elemental carbon (soot) particles, and inorganic particles containing substantial signal due to ions includ ing Al⁺, Ca⁺, Fe⁺, Ba⁺ and BaO⁺. Preliminary analysis of these classes shows that they encompass 61.4%, 10.3%, and 11.0%, respectively, of the total number of particles sampled with the ATOFMS instrument in 3 h, heavy traffic sampling periods, in an LDV-only bore of the tunnel. They represent 57.4%, 11.8%, and 18.0%, respectively, of the total number of particles sampled with the ATOFMS instrument in a 3 h sampling period in a mixed traffic (HDV and LDV) bore of the tunnel.     

Reproducibility of Single Particle Chemical Composition during a Heavy Duty Diesel Truck Dynamometer Study

The chemical reproducibility of single particle mass spectrometry (SPMS) instruments is complicated by numerous factors, including uncertainties in the laser desorption/ionization process leading to shot-to-shot variability in single particle mass spectra, excessive fragmentation of carbonaceous species, as well as a relatively low duty cycle (1-10 Hz). With source apportionment being a major application for these instruments, proper source profiles must be determined from major aerosol sources. This brief communication illustrates, for the first time, the chemical reproducibility of an aerosol time-of-flight mass spectrometer (ATOFMS) sampling highly transient heavy duty diesel (HDD) truck exhaust emissions from a transportable heavy duty vehicle emissions testing laboratory, which includes a dilution tunnel as well as a residence chamber.In addition to examining the reproducibility of ATOFMS using a complex mixture of "real" aerosol particles, the chemical reproducibility of a dynamometer system at the single particle level is tested. The results presented indicate that for future studies, truck-to-truck and source-to-source variations can be attributed to chemical differences and not just to innate variations due to instrumental variability.     

Characterization of Organic Particles from Incense Burning Using an Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer

Incense burning is a common ritual in Asian communities both indoors in residential homes and outdoors in temple premises. Organic particles from burning of incense sticks, incense coils, and mosquito coils after extensive dilution (>1000×) were characterized by the Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). The obtained mass spectra in general resemble those reported for biomass burning aerosols. Ion peaks with m/z values higher than 100 accounted for 15%–25% of the organic signals in the unit-mass-resolution (UMR) mass spectra. In the high-resolution (HR) mass spectra, the ion peaks at m/z 60 and 73 are found to be related to the sugar anhydrides as in particles from other biomass burning processes. In addition, the ion peaks at m/z 107, 121, 137, 151, 167, and 181, some of which (e.g., m/z 137 and 167) have been observed in particles from biomass burning but not yet assigned, were assigned to lignin-related components. Elemental analysis from the HR data reveals that a large portion of particulate organics from incense burning are oxygenated (O/C between 0.3 and 0.5) and unsaturated (and/or cyclic) in nature. Results from this study also highlight that mass spectra from HR-ToF-AMS measurements concerning primary emissions such as incense burning contain very useful information in the high m/z (>100) region about the chemical characteristics of those primary organic particles.

Copyright 2012 American Association for Aerosol Research     

Screening of Aerosol Filter Samples for PAHs and Nitro-PAHs by Laser Desorption Ionization TOF Mass Spectrometry

Direct and selective screening of aerosol particulate matter for polycyclic aromatic hydrocarbons (PAHs) and nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) is achieved using laser desorption ionization time-of-flight (LDI TOF) mass spectrometry. Desorption and ionization of collected aerosol particulate matter was accomplished using pulsed UV radiation at 266 nm. PAHs were detected in positive ion spectra, while nitro-PAHs were selectively detected in negative ion spectra. Direct laser desorption ionization circumvents extraction procedures necessary for HPLC or gas chromatography/mass spectrometry (GC/MS) analyses, and such screening offers potential cost saving by identifying samples which contain too little PAH for GC/MS analyses to be productive. Applicability of the LDI TOF method was demonstrated by collecting aerosol particles of less than 2.5 mu m aerodynamic diameter (PM 2 . 5) on Teflon filters from inside an urban bus terminal. Sampling of small air volumes (0.32-0.98 m3) was sufficient for LDI TOF analysis. Positive ion mass spectra of all collected aerosol samples exhibited peaks attributed to a wide range of PAHs. Of primary importance, selective ionization and detection of less abundant and more toxic nitro-PAHs is demonstrated in the negative ion spectra. GC/MS analyses of duplicate filters confirmed laser desorption ionization analyses and assisted identification of specific PAH isomers.     

Instrument Busy Time and Mass Measurement using Aerosol Time-of-Flight Mass Spectrometry

Aerosol Time-of-Flight Mass Spectrometry (ATOFMS) instruments have been used widely to measure the size and composition of single ambient aerosol particles. ATOFMS data do not directly and quantitatively represent aerosol composition because the instruments exhibit non-linear response to particle concentration, size, and composition. Our approach is to analyze separately the components of non-linear ATOFMS response using field sampling data in order to understand ATOFMS response to ambient aerosols so that ATOFMS data can be scaled to more closely represent ambient aerosols. In this work we examine the effect of instrument busy time, mainly the time to process and save data, on ATOFMS response to ambient aerosols sampled during the 1999 Bakersfield Instrument Intercomparison Study (BIIS). During this study an ATOFMS instrument was operated alternately in normal and fast scatter data acquisition modes. In fast scatter mode, the instrument does not record mass spectra, minimizing instrument busy time; these data were used to determine particle arrival rates. Busy time in normal mode was found by a comparison of the number of particles detected to that expected for a Poisson process modified to include busy time. During the BIIS experiment, the ATOFMS instrument was busy between 5 and 95% of the nominal sampling time; thus busy time cannot be ignored for accurate quantitative analysis of ATOFMS data. ATOFMS data were scaled for on-line time and transmission efficiency, found by comparison with reference aerosol measurements, in order to estimate fine particle mass concentrations. Fine aerosol mass concentrations from scaled ATOFMS data demonstate semi-quantitative agreement with independent measurements using Beta Attenuation Monitors. We recommend that ATOFMS instruments be modified to measure busy time directly.     

New Methodology for Quantifying Polycyclic Aromatic Hydrocarbons (PAHs) Using High-Resolution Aerosol Mass Spectrometry

This article presents a new methodology to potentially quantify polycyclic aromatic hydrocarbon (PAH) isomers using high-resolution time of flight aerosol mass spectrometer (HR-AMS). The fragmentation of PAHs within the HR-AMS is such that significant signal remains at the molecular ion. After quantifying the molecular ion signal and taking into account potential interferences, the amount of the parent PAH in the aerosol may be inferred once its fragmentation pattern is also known. The potential of this approach was evaluated using mixed gasoline and diesel engine exhaust sampled under varying conditions. This dataset led to the identification and quantification within the aerosol mass spectra of the molecular ions associated with 53 PAH isomers, including both unsubstituted and functionalized species. An evaluation of anticipated interferences shows that interferences from larger molecular weight PAHs (i.e., PAH/PAH interferences) could be constrained based on the fragmentation behavior of PAHs from existing HR-AMS laboratory spectra. Other signal interferences for this data set are typically less than 5% of the total signal or, for ¹³C isotopic interferents, are well constrained by measurements of the dominant isotope. The experimental data reveal that the fractional PAH molecular ion signal remained stable despite dramatic temporal variability of the total particulate organic signal. The fractional contributions of the molecular ions for grouped PAH species and even individual compounds were remarkably consistent across experiments. The distribution of PAHs showed no apparent dependence on engine load or exhaust type. Full application of this approach will require a greater number of standard HR-AMS spectra for PAHs, so that the relationship between compounds and their molecular ions may be understood more precisely.

Copyright 2015 American Association for Aerosol Research     

Impacts of Aerosol Aging on Laser Desorption/Ionization in Single-Particle Mass Spectrometers

Single-particle mass spectrometry (SPMS) has been widely used for characterizing the chemical mixing state of ambient aerosol particles. However, processes occurring during particle ablation and ionization can influence the mass spectra produced by these instruments. These effects remain poorly characterized for complex atmospheric particles. During the 2005 Study of Organic Aerosols in Riverside (SOAR), a thermodenuder was used to evaporate the more volatile aerosol species in sequential temperature steps up to 230°C; the residual aerosol particles were sampled by an aerosol mass spectrometer (AMS) and a single-particle aerosol time-of-flight mass spectrometer (ATOFMS). Removal of the secondary species (e.g., ammonium nitrate/sulfate) through heating permitted assessment of the change in ionization patterns as the composition changed for a given particle type. It was observed that a coating of secondary species can reduce the ionization efficiency by changing the degree of laser absorption or particle ablation, which significantly impacted the measured ion peak areas. Nonvolatile aerosol components were used as pseudo-internal standards (or “reference components”) to correct for this LDI effect. Such corrected ATOFMS ion peak areas correlated well with the AMS measurements of the same species up to 142°C. This work demonstrates the potential to accurately relate SPMS peak areas to the mass of specific aerosol components.

Copyright 2014 American Association for Aerosol Research     

Organic PM Emissions from Vehicles: Composition,O/C Ratio,and Dependence on PM Concentration

A suite of real-time instruments was used to sample vehicle emissions at the California Air Resources Board Haagen-Smit facility. Eight on-road, spark-ignition gasoline and three alternative vehicles were tested on a chassis dynamometer and the emissions were diluted to atmospherically relevant concentrations (0.5–30 μg/m³). An Aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-ToF-MS) characterized the real-time behavior of the nonrefractory organic and inorganic particulate matter (PM) in vehicle emissions. It was found that the emission of particulate organic matter (POM) was strongly affected by engine temperature and engine load and that the emission concentrations could vary significantly by vehicle. Despite the small sample size, consistent trends in chemical characteristics were observed. The composition of vehicle POM was found to be related to overall PM mass concentration where the oxygen-to-carbon (O/C) ratio tended to increase at lower concentration and had an average value of 0.057 ± 0.047, with a range from 0.022 to 0.15. The corresponding fraction of particle-phase CO₂⁺, or f₄₄, ranged from 1.1% to 8.6% (average = 2.1%) and exhibited a linear variation with O/C. The average mass spectrum from all vehicles tested was also compared to those of hydrocarbon-like organic aerosol (HOA) observed in ambient air and the agreement is very high. The results of these tests offer the vehicle emissions community a first glimpse at the real-time chemical composition and variation of vehicle PM emissions for a variety of conditions and vehicle types at atmospherically relevant conditions and without chemical interferences from other primary or secondary aerosol sources.

Copyright 2015 American Association for Aerosol Research     

Characteristics of polycyclic aromatic hydrocarbons emissions of diesel engine fueled with biodiesel and diesel

With mutagenic and carcinogenic potential, polycyclic aromatic hydrocarbons (PAHs) from mobile source exhaust have contributed to a substantial share of air toxics. In order to characterize the PAHs emissions of diesel engine fueled with diesel, biodiesel (B100) and its blend (B20), an experimental study has been carried out on a direct-injection turbocharged diesel engine. The particle-phase and gas-phase PAHs in engine exhaust were collected by fiberglass filters and “PUF/XAD-2/PUF” cartridges, respectively, then the PAHs were determined by a gas chromatograph/mass spectrometer (GC/MS). The experimental results indicated that comparing with diesel, using B100 and B20 can greatly reduce the total PAHs emissions of diesel engine by 19.4% and 13.1%, respectively. The Benzo[a]Pyrene (BaP) equivalent of PAHs emissions were also decreased by 15.0% with the use of B100. For the three fuels, the gas-phase PAHs emissions were higher than particle-phase PAHs emissions and the most abundant PAH compounds from engine exhaust were naphthalene and phenanthrene. The analysis showed that there was a close correlation between total PAHs emissions and particulate matter (PM) emissions for three fuels. Furthermore, the correlation became more significant when using biodiesel.     

Real-Time Characterization of the Composition of Individual Particles Emitted From Ultrafine Particle Concentrators

Particle concentrators are commonly used for controlling exposure levels to ambient ultrafine, fine, and coarse aerosols over a broad range of concentrations. For ultrafine aerosols, these concentrators require water condensation technology to grow and enrich these smaller sized particles (D _a < 100 nm). Because the chemistry of the particles is directly related to their toxicity, any changes induced by ultrafine concentrators on ambient particles need to be better characterized in order to fully understand the results obtained in health exposure studies. Using aerosol time-of-flight mass spectrometry (ATOFMS), the size-resolved chemistry was measured of concentrated ultrafine and accumulation mode (50–300 nm) particles from several particle concentrators with different designs. This is the first report detailing the size-resolved distributions of elemental carbon (EC) and organic carbon (OC) particles sampled from concentrators. Experimental measurements of the single particle mixing state of particles in concentrated versus non-concentrated ambient air show transformations of ultrafine EC particles occur as they become coated with organic carbon (OC) species during the concentration process. Based on relative ion intensities, concentrated ultrafine particles showed a 30% increase in the amount of OC on the EC particles for the same aerodynamic size. An increase in the number fraction of aromatic- and polycyclic aromatic hydrocarbon-containing particles was also observed in both the ultrafine and fine size modes. The most likely explanation for such changes is gas-to-particle partitioning of organic components (e.g., water-soluble organic compounds) from the high volume of air used in the concentrator into aqueous phase ultrafine and fine aqueous particles created during the particle enrichment process.     

An Intercomparison of Measurement Methods for Carbonaceous Aerosol in the Ambient Air in New York City

Measurement methods for fine carbonaceous aerosol were compared under field sampling conditions in Flushing, New York during the period of January and early February 2004. In-situ 5- to 60-minute average PM _2.5 organic carbon (OC), elemental carbon (EC), and black carbon (BC) concentrations were obtained by the following methods: Sunset Laboratory field OC/EC analyzer, Rupprecht and Patashnick (R&P) series 5400 ambient carbon particulate monitor, Aerodyne aerosol mass spectrometer (AMS) for total organic matter (OM), and a two-wavelength AE-20 Aethalometer. Twenty-four hour averaged PM _2.5 filter measurements for OC and EC were also made with a Speciation Trends Network (STN) sampler. The diurnal variations in OC/EC/BC concentrations peaked during the morning and afternoon rush hours indicating the dominant influence of vehicle emissions. BC/EC slopes are found to range between 0.86 and 1.23 with reasonably high correlations (r > 0.75). Low mixing heights and absence of significant transported carbonaceous aerosol are indicated by the measurements. Strong correlations are observed between BC and thermal EC as measured by the Sunset instrument and between Sunset BC and Aethalometer BC. Reasonable correlations are observed among collocated OC/EC measurements by the various instruments.     

Matrix-assisted laser desorption/ionisation aerosol time-of-flight mass spectrometry for the analysis of bioaerosols: development of a fast detector for airborne biological pathogens

A new aerosol time-of-flight mass spectrometer (ATOFMS) was developed for the near real-time analysis of single bioaerosol particles. The system combines ATOFMS with laser-induced fluorescence selection and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The influences of laser power and sample preparation on the quality of the mass spectra have been investigated. A narrow range of laser fluence gives the optimal signals in the mass spectra. On-line application of ferulic acid provides spectra with quality comparable to other preparation methods. The system can analyze aerosolized proteinaceous material up to 20,000 Da, which is the range of the molecular masses of marker ions of bacteria. The results of a preliminary test with spores of B. subtilis var niger show a good prospect for application in the identification of single bacteria and spores. The obtained spectra are promising, although more research is necessary to increase the resolution and accuracy of the spectra.     

Seasonal and Spatial Variation of Polycyclic Aromatic Hydrocarbons in Vapor-Phase and PM2.5 in Southern California Urban and Rural Communities

Fifteen priority polycyclic aromatic hydrocarbons (PAHs) were measured in two rural communities (Atascadero and Lompoc) located several hundred km northwest of Los Angeles and in four urban communities 40–100 km downwind of Los Angeles (San Dimas, Upland, Mira Loma, and Riverside), during all seasons, from May 2001 to July 2002. PM_2.5 and vapor-phase PAHs were collected, on prebaked quartz fiber filters and PUF-XAD-4 resin, respectively, at 113 LPM, during 24 h periods, every eighth day, and quantified by HPLC-Fluorescence. At all sites vapor-phase PAHs contained > 99.9% of the total PAH mass and were dominated by naphthalene (NAP), which varied from about 60 ng m ^{? 3} in Lompoc, a community with light traffic, to ～580 ng m ^{? 3} in Riverside, a community traversed by ～200,000 vehicles day^{? 1}. During summer pollution episodes in urban sites, NAP concentrations reached 7–30 times annual averages. Except for summer episodes, concentrations of low MW PAHs showed small seasonal variations (～2 times higher in winter). Similar concentrations of particle-phase PAHs were observed at all sites except for Lompoc. Benzo[ghi]perylene (BGP), a marker of gasoline exhaust emissions, showed the highest concentration among particle-phase PAHs, varying from 23.3 pg m^?3 in Lompoc to 193 pg m^?3 in Mira Loma. Benzo[a]pyrene and indeno[1,2,3-cd]pyrene, found exclusively in the particle phase, were much higher in urban sites (～40–100 pg m^?3), than in Lompoc (～12 pg m^?3). Winter particle-phase PAHs were 2 to 14 times higher than summer levels. Particle-phase PAHs were negatively correlated with mean air temperature in urban sites (r = ?0.50 to ?0.75), probably resulting from surface inversions occurring during winter. The data suggest that in Southern California vehicular exhaust emissions are a major contributor to particle-phase PAHs.     

More unsaturated,cooking-type hydrocarbon-like organic aerosol particle emissions from renewable diesel compared to ultra low sulfur diesel in at-sea operations of a research vessel

The aerosol particle emissions from R/V Robert Gordon Sproul were measured during two 5-day research cruises (29 September–3 October 2014; 4–7 and 26–28 September 2015) at four engine speeds (1600 rpm, 1300 rpm, 1000 rpm, and 700 rpm) to characterize the emissions under different engine conditions for ultra low sulfur diesel (ULSD) and hydrogenation derived renewable diesel (HDRD) fuels. Organic aerosol composition and mass distribution were measured on the aft deck of the vessel directly behind the exhaust stack to intercept the ship plume. The ship emissions for both fuels were composed of alkane-like compounds (H/C = 1.94 ± 0.003, O/C = 0.04 ± 0.001, C_nH_2n) with mass spectral fragmentation patterns consistent with hydrocarbon-like organic aerosol (HOA). Single-particle mass spectra from emissions for both fuels showed two distinct HOA compositions, with one HOA type containing more saturated alkane fragments (C_nH_2n+1) and the other HOA type containing more monounsaturated fragments (C_nH_2n?1). The particles dominated by the C_nH_2n?1 fragment series are similar to mass spectra previously associated with cooking emissions. More cooking-type organic particles were observed in the ship emissions for HDRD than for ULSD (45% and 38%, respectively). Changes in the plume aerosol composition due to photochemical aging in the atmosphere were also characterized. The higher fraction of alkene or aromatic (C_nH_2n?m, m ≥ 3) fragments in aged compared to fresh plume emissions suggest that some of the semivolatile alkane-like components partition back to the vapor phase as dilution increases, while alkene or aromatic hydrocarbons contribute more mass to the particle phase due to continuing photochemical oxidation and subsequent condensation from the vapor phase.

Copyright © 2017 American Association for Aerosol Research     

Physical and chemical characterization of aerosol in fresh and aged emissions from open combustion of biomass fuels

Biomass burning (BB) emissions and their atmospheric oxidation products can contribute significantly to direct aerosol radiative forcing of climate. Limited knowledge of BB organic aerosol chemical and optical properties leads to large uncertainties in climate models. In this article, we describe the experimental setup and the main findings of a laboratory BB study aimed at comprehensive optical, physical, and chemical characterization of fresh and aged BB emissions. An oxidation flow reactor (OFR) was used to mimic atmospheric oxidation processes. The OFR was characterized in terms of OH? production rate, particle transmission efficiency, and characteristic lifetimes of condensible compounds. Emission factors (EFs) of main air pollutants (particulate matter, organic carbon [OC], elemental carbon [EC], carbon monoxide [CO], and nitrogen oxides [NO_x]) were determined for five globally and regionally important biomass fuels: Siberian (Russia), Florida (USA), and Malaysian peats; mixed conifer and aspen fuel from Fishlake National Forest, Utah, USA; and mixed grass and brush fuel representative of the Great Basin, Nevada, USA. Measured fuel-based EFs for OC ranged from 0.85?±?0.24 to 6.56?±?1.40?mg g^?1. Measured EFs for EC ranged from 0.02?±?0.01 to 0.16?±?0.01?mg g^?1. The ratio of organic mass to total carbon mass for fresh emissions from these fuels ranged from 1.04?±?0.04 to 1.34?±?0.24. The effect of OFR aging on aerosol optical properties, size distribution, and concentration is also discussed.

Copyright © 2018 American Association for Aerosol Research     

Water-Particle Distribution of Hydrophobic Micro Pollutants in Storm Water Runoff

Sorptive behaviors of polycyclic aromatic hydrocarbons (PAHs) as well as other classes of hydrophobic pollutants (i.e., n-alkanes and linear alkylbenzenes: LABs) were investigated for street runoff and for particle-size segregated river water samples. PAHs, except for 3-ring aromatics, were mostly transported with particles >1.2μm. In all the environmental samples PAHs were more hydrophobic than expected from their Kow; whereas vigorous mixing of road dust with water for 24 hours resulted in more desorption of PAHs into the aqueous phase. It indicates that although strongly associated with particles, at least some part of the “particle bound” PAHs could be available for active exchange wirh their dissolved counterparts. As opposed to PAHs, n-alkanes and LABs revealed less hydrophobic nature than expected from Kow, although their majorities were in “particulate form”.     

Development of a High-Pressure Aerodynamic Lens for Focusing Large Particles (4–10 μm) into the Aerosol Time-of-Flight Mass Spectrometer

A new aerodynamic lens system for an online aerosol time-of-flight mass spectrometer (ATOFMS) has been designed and constructed to transmit and allow the analysis of individual particles in the 4–10-μm-size range. Modeling was used to help design the lens within the bounds of ATOFMS instrumental constraints. The aerodynamic lens operates at a high inlet pressure, 3066 Pa (23 Torr), with a unique tapered relaxation region to improve large particle transmission. Every stage of the lens was tested empirically using a combination of particle deposition and light scattering experiments. The critical orifice was found to significantly impact large particle transmission, with orifices <200 μm in diameter completely suppressing large particle transmission. The addition of a virtual impactor allowed for the use of large orifices without any loss of functionality in the ATOFMS. The detection efficiency of the ATOFMS was >10% for particles from 4–10 μm with a peak efficiency of 74 ± 9% for 6-μm particles. With the extended size range provided by this inlet, the ATOFMS can now be extended to investigate single cell metabolomics.

Copyright 2014 American Association for Aerosol Research     

An Intensive Study of the Size and Composition of Submicron Atmospheric Aerosols at a Rural Site in Ontario,Canada

Atmospheric sampling was conducted at a rural site near Egbert, about 70 km north of Toronto, Ontario, Canada from March 27 to May 8, 2003 to characterize the physical and chemical properties of the ambient aerosol in near real-time. The instrumentation included a tapered element oscillating microbalance (TEOM), an ultrafine condensation particle counter (UCPC), a scanning mobility particle sizer (SMPS), an aerodynamic particle sizer (APS), an aerosol mass spectrometer (AMS), and a particulate nitrate monitor (R&P 8400N) for aerosol measurements. Gas-phase non-methane hydrocarbon compounds (NMHCs) were measured by gas chromatograph-flame ionization detection (GC-FID). Filter samples were also collected for analysis of inorganic ions by ion chromatography (IC). Aerosol properties varied considerably depending upon meteorological conditions and airmass histories. For example, urban and industrial emissions advected from the south strongly influenced the site occasionally, resulting in higher particulate mass with the higher fractions of nitrate and organics. Cleaner northwesterly winds carried aerosols with relatively higher fractions of organics and sulfate. The AMS derived mass size distributions showed that the inorganic species in the particles with vacuum aerodynamic diameters between about 60 nm and 600 nm had mass modal vacuum aerodynamic diameters around 400–500 nm. The particulate organics often exhibited two modes at about 100 nm and 425 nm, more noticeable during fresh pollution events. The small organic mode was well correlated with gas-phase nonmethane hydrocarbons such as ethylbenzene, toluene, and propene, suggesting that the likely sources of small organic particles were combustion related emissions. The particulate nitrate exhibited a diurnal variation with higher concentrations during dark hours and minima in the afternoon. Particulate sulfate and organics showed evidence of photochemical processing with higher levels of sulfate and oxygenated organics in the afternoon. Reasonable agreement among all of the co-located measurements is found, provided the upper size limit of the AMS is considered.     

Determination of Polycyclic Aromatic Hydrocarbons in F-15J,C-130H,and F-4EJ Aircraft Exhaust

There are occupational health concerns at Japan Air Self-Defense Force bases in regard to the exposure of military flightline personnel to carcinogens in aircraft emissions, such as polycyclic aromatic hydrocarbons (PAHs). To characterize the PAHs in military aircraft emissions from different types of engines, aerosol and gas samples were separately collected downwind from aircraft with a turboprop engine (C-130H), turbojet (F-4EJ), and turbofan (F-15J). The gas-phase PAHs were determined by gas chromatography coupled to mass spectrometry and the aerosol-phase PAHs were determined by high-performance liquid chromatography with fluorescence detection. The F-4EJ engine was a source of naphthalene vapor and aerosol PAHs, including carcinogens such as chrysene, benzo (b) fluoranthene, benzo (k) fluoranthene, benzo (a) pyrene, dibenzo (a,h) anthracene, benzo (ghi) perylene, and indeno (1,2,3-cd) pyrene. These heavier (five and six-ring) PAHs were also included in the emissions from the F-15J with its newer, high-temperature F-100 turbofan engine, but the concentrations were approximately one-tenth of those in the F-4EJ. In contrast to these fighter aircraft, the C-130H was found to be a significant aerosol source of the lighter, three-ring (phenanthrene and anthracene) and four-ring (fluoranthene and pyrene) PAHs, but not the heavier ones. These results demonstrate that various aircraft are sources of PAHs in the military flightline environment.