Direct Observation of Particle-To-Particle Variability in Ambient Aerosol pH Using a Novel Analytical Approach Based on Surface-Enhanced Raman Spectroscopy.

The pH of atmospheric aerosols is a key characteristic that profoundly influences their impacts on climate change, human health, and ecosystems. Despite widely performed aerosol pH research, determining the pH levels of individual atmospheric aerosol particles has been a challenge. This study presents a novel analytical technique that utilizes surface-enhanced Raman spectroscopy to assess the pH of individual ambient PM2.5-10 aerosol particles in conjunction with examining their hygroscopic behavior, morphology, and elemental compositions. The results revealed a substantial pH variation among simultaneously collected aerosol particles, ranging from 3.3 to 5.7. This variability is likely related to each particle's unique reaction and aging states. The extensive particle-to-particle pH variability suggests that atmospheric aerosols present at the same time and location can exhibit diverse reactivities, reaction pathways, phase equilibria, and phase separation properties. This pioneering study paves the way for in-depth investigations into particle-to-particle variability, size dependency, and detailed spatial and temporal variations of aerosol pH, thus deepening our understanding of atmospheric chemistry and its environmental implications.

Millennial-scale variability of Greenland dust provenance during the last glacial maximum as determined by single particle analysis.

Greenland ice core records exhibited 100-fold higher dust concentrations during the Last Glacial Maximum (LGM) than during the Holocene, and dust input temporal variability corresponded to different climate states in the LGM. While East Asian deserts, the Sahara, and European loess have been suggested as the potential source areas (PSAs) for Greenland LGM dust, millennial-scale variability in their relative contributions within the LGM remains poorly constrained. Here, we present the morphological, mineralogical, and geochemical characteristics of insoluble microparticles to constrain the provenance of dust in Greenland NEEM ice core samples covering cold Greenland Stadials (GS)-2.1a to GS-3 (~ 14.7 to 27.1 kyr ago) in the LGM. The analysis was conducted on individual particles in microdroplet samples by scanning electron microscopy with energy dispersive X-ray spectroscopy and Raman microspectroscopy. We found that the kaolinite-to-chlorite (K/C) ratios and chemical index of alteration (CIA) values were substantially higher (K/C: 1.4 ± 0.7, CIA: 74.7 ± 2.9) during GS-2.1a to 2.1c than during GS-3 (K/C: 0.5 ± 0.1, CIA: 65.8 ± 2.8). Our records revealed a significant increase in Saharan dust contributions from GS-2.1a to GS-2.1c and that the Gobi Desert and/or European loess were potential source(s) during GS-3. This conclusion is further supported by distinctly different carbon contents in particles corresponding to GS-2.1 and GS-3. These results are consistent with previous estimates of proportional dust source contributions obtained using a mixing model based on Pb and Sr isotopic compositions in NEEM LGM ice and indicate millennial-scale changes in Greenland dust provenance that are probably linked to large-scale atmospheric circulation variabilities during the LGM.

Novel Single-Particle Analytical Technique for Inhalable Airborne Microplastic Particles by the Combined Use of Fluorescence Microscopy, Raman Microspectrometry, and SEM/EDX.

This study presents a novel and efficient method for analyzing inhalable airborne microplastics (AMPs) in ambient PM10 aerosols. Although many studies have been conducted on MPs in a variety of environments, the physicochemical characteristics of AMPs of inhalable size (<10 µm) in ambient PM10 are poorly understood because of the lack of suitable analytical methods. The method employed in this study combines fluorescence microscopy, Raman microspectrometry (RMS), and scanning electron microscopy/energy-dispersive X-ray spectrometry (SEM/EDX) for an efficient and reliable investigation of inhalable AMPs, which constitute a small portion of ambient PM10 aerosol particles. Fluorescence microscopy and staining are used to select particles with high MP potential from ambient urban PM10 aerosols. The combination of RMS and SEM/EDX then allows for a detailed characterization of these particles on a single-particle basis. The results of the study show that ∼0.008% of the particles collected using a PM10 sampler had high MP potential, corresponding to ∼800 particles/m3. Among the stained particles of <10 µm, 27% were determined to be plastic, while the remaining 73% were found to be from tire/road wear. The number of inhalable AMPs was estimated to be 192 (±127) particles/m3. This study provides an important insight into the characteristics of inhalable AMPs in ambient PM10 aerosols that are particularly critical in respect of human health and climate change. The authors highlight that the use of a single fluorescence staining method can overestimate the number of inhalable AMPs in ambient air by including tire/road wear particles. To the best of their knowledge, this is the first study to demonstrate the morphological and spectroscopic characteristics of the same individual inhalable AMPs.

Novel Single-Particle Analytical Technique for Submicron Atmospheric Aerosols: Combined Use of Dark-Field Scattering and Surface-Enhanced Raman Spectroscopy.

Raman microspectrometry (RMS) is a useful single particle analysis method that can provide information on the mixing states, molecular species, and chemical functional groups of individual aerosol particles, which are difficult to determine by bulk analysis techniques. On the other hand, drawbacks, such as low Raman cross-section, spatial resolution (∼1 µm), and optical diffraction limit, make the analysis of atmospheric particles in the submicron size range difficult using conventional RMS. This study developed a new strategy to detect individual submicron-size atmospheric particles by combining dark-field (DF) microscopy and surface-enhanced Raman spectroscopy (SERS). The DF technique overcomes optical spatial diffraction limit by contrast enhancement, allowing the visualization of submicron particles. SERS facilitates spectroscopic characterization (obtaining information on molecular fingerprints and mixing states) of trace amounts of analyte by increasing the Raman scattering cross-section at the hot spot. SERS-active silver substrates sputter-coated on a Si wafer efficiently provided a clear background in the dark-field image and uniform hot spots over a large area, which were suitable for single-particle analysis. Various functional groups in individual particles and their heterogeneous mixing states were investigated, demonstrating the potential of this method to provide improved information on submicron atmospheric particles of femtogram-level masses. DF-SERS may elucidate the detailed physicochemical characteristics of individual submicron particles, providing new information on the formation mechanisms and fates of atmospheric particles.

Hygroscopic behavior and chemical reactivity of aerosols generated from mixture solutions of low molecular weight dicarboxylic acids and NaCl.

Ambient sea spray aerosols (SSAs) have been reported to undergo reactions with low molecular weight dicarboxylic acids (LMW DCAs). In the present study, the hygroscopic behavior of aerosols generated from NaCl-LMW DCA mixture solutions with different mixing ratios was explained. In situ Raman microspectrometry (RMS) was used to simultaneously monitor the alterations in chemical composition, size, and phase as a function of the relative humidity (RH) for individual aerosols. The observation of individual mixture aerosols revealed chemical reactions on the timescale of one hour in the aqueous phase, mostly during the dehydration process, leading to the formation of sodium salts of DCAs with distinct reactivities among different DCAs and mixing ratios, which in turn exhibited diverse hygroscopic behaviors. The NaCl-DCA mixture aerosols were either in a ternary NaCl-DCA-DCA sodium salt system or a binary NaCl-DCA sodium salt or DCA-DCA sodium salt system, instead of a binary NaCl-DCA system when experiencing the hygroscopic process. The chemical compositional evolution of the NaCl-DCA aerosols during the hygroscopic measurements was examined based on the Raman spectra acquired for aqueous, amorphous, and/or crystalline pure standard aerosols at specific RHs. The different reactivity observed among the DCAs with different mixing ratios suggests that the reactivity driven by the irreversible liberation of HCl is governed mainly by the available aqueous H+ because Cl- is always available in the aqueous NaCl-DCA aerosols until the complete consumption of NaCl.

Multi-Modal Compositional Analysis of Layered Paint Chips of Automobiles by the Combined Application of ATR-FTIR Imaging, Raman Microspectrometry, and SEM/EDX.

For the forensic analysis of multi-layered paint chips of hit-and-run cars, detailed compositional analysis, including minor/trace chemical components in the multi-layered paint chips, is crucial for the potential credentials of the run-away car as the number of layers, painting process, and used paints are quite specific to the types of cars, color of cars, and their surface protection depending on the car manufacturer and the year of manufacture, and yet overall characteristics of some paints used by car manufacturers might be quite similar. In the present study, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) imaging, Raman microspectrometry (RMS), and scanning electron microscopy/energy-dispersive X-ray spectrometric (SEM/EDX) techniques were performed in combination for the detailed characterization of three car paint chip samples, which provided complementary and comprehensive information on the multi-layered paint chips. That is, optical microscopy, SEM, and ATR-FTIR imaging techniques provided information on the number of layers, physical heterogeneity of the layers, and layer thicknesses; EDX on the elemental chemical profiles and compositions; ATR-FTIR imaging on the molecular species of polymer resins, such as alkyd, alkyd-melamine, acrylic, epoxy, and butadiene resins, and some inorganics; and RMS on the molecular species of inorganic pigments (TiO2, ZnO, Fe3O4), mineral fillers (kaolinite, talc, pyrophyllite), and inorganic fillers (BaSO4, Al2(SO4)3, Zn3(PO4)2, CaCO3). This study demonstrates that the new multi-modal approach has powerful potential to elucidate chemical and physical characteristics of multi-layered car paint chips, which could be useful for determining the potential credentials of run-away cars.

Alveolar macrophage reaction to PM2.5 of hazy day in vitro: Evaluation methods and mitochondrial screening to determine mechanisms of biological effect.

Hazy weather in China has recently become a major public health concern due to high levels of atmospheric fine particulate matter (PM2.5) with a large amount of polycyclic aromatic hydrocarbon (PAHs). In this study, the mass concentration of PAHs in hazy PM2.5 in urban Taiyuan city, China was determined and toxicities of different dosage of the hazy PM2.5 on rat alveolar macrophages (AMs) were examined. It was found that the hazy PM2.5, bounded with many species of PAHs (CHR, BbF, BaP, BaA, and etc.), significantly increased cellular malondialdehyde (MDA) content followed by the decreasing in superoxide (SOD) and glutathione peroxidase (GPx) in AMs. They induced mitochondrial changes in ultrastructure as evidenced by mitochondrial swelling and cristae disorganization, and a dose-dependent decrease in mitochondrial profile density. Also, the mRNA expression levels of mitochondrial fusion-related genes were modified. The Mfn1 and Mfn2 which are essential for mitochondrial fusion increased significantly in hazy PM2.5-treated group compared to the control in a dose-dependent manner, OPA1 was significantly increased at the highest PM2.5 dose delivered. These findings suggested that exposure to hazy PM2.5 could activate oxidative stress pathways in AMs, resulting in abnormal mitochondrial morphology and fusion/fission frequency. Possibly, the toxic effects were mostly attributed to the high burden of varied PAHs in hazy PM2.5.

Relationship between reactive oxygen species and water-soluble organic compounds: Time-resolved benzene carboxylic acids measurement in the coastal area during the KORUS-AQ campaign.

This study investigated the relationship between water-soluble organic compounds of ambient particulate matter (PM) and cellular redox activity collected from May 28 to June 20 of 2016 at the west coastal site in the Republic of Korea during the KORea-US Air Quality (KORUS-AQ) campaign. Automatic four-hour integrated samples operated at a flow rate of 92 L per minute for the analysis of organic carbon (OC), water-soluble organic carbon (WSOC), elemental carbon (EC), water-soluble ions (WSIs), and benzene carboxylic acids (BCAs) were collected on a 47 mm quartz fiber filter. The influence of atmospheric transport processes was assessed by the Weather Research and Forecasting (WRF) model. OC, EC, WSOC, and BCA were determined by SUNET carbon analyzer, total organic carbon (TOC) analyzer, and liquid chromatography-mass spectrometry mass spectrometry (LC-MSMS), respectively. Twenty-four-hour integrated samples were collected for reactive oxygen species (ROS) analysis using a fluorogenic cell-based method to investigate the main chemical classes of toxicity. The results illustrate that WSOC and specific water-soluble species are associated with the oxidative potential of particulate matter. Pairwise correlation scatterplots between the daily-averaged WSOC and ROS (r2 of 0.81), and 135-BCA and ROS (r2 of 0.84), indicate that secondary organic aerosol production was highly associated with ROS activity. In addition, X-ray spectral analysis together with secondary electron images (SEIs) of PM2.5 particles collected during high ROS concentration events clearly indicate that water-soluble organic aerosols are major contributors to PM2.5 mass. This study provides insight into the components of particulate matter that are drivers of the oxidative potential of atmospheric particulate matter and potential tracers for this activity.

Real-Time Investigation of Chemical Compositions and Hygroscopic Properties of Aerosols Generated from NaCl and Malonic Acid Mixture Solutions Using in Situ Raman Microspectrometry.

Recently, ambient sea spray aerosols (SSAs) have been reported to undergo reactions with dicarboxylic acids (DCAs). Several studies have examined the hygroscopic behavior and chemical reactivity of aerosols generated from NaCl-DCA mixture solutions, but the results have varied, especially for the NaCl-malonic acid (NaCl-MA) mixture system. In this work, in situ Raman microspectrometry (RMS) was used to simultaneously monitor the change in chemical composition, size, and phase as a function of the relative humidity, for individual aerosols generated from NaCl-MA solutions, during two hygroscopic measurement cycles, which were performed first through the dehydration process, followed by a humidification process, in each cycle. In situ RMS analysis for the aerosols showed that the chemical reaction between NaCl and MA occurred rapidly in the time scale of 1 h and considerably in the aqueous phase, mostly during the first dehydration process, and the chemical reaction occurs more rapidly when MA is more enriched in the aerosols. For example, the reaction between NaCl and MA for aerosols generated from solutions of NaCl:MA = 2:1 and 1:2 occurred by 81% and 100% at RH = 42% and 45%, respectively, during the first dehydration process. The aerosols generated from the solution of NaCl:MA = 2:1 revealed single efflorescence and deliquescence transitions repeatedly during two hygroscopic cycles. The aerosols from NaCl:MA = 1:1 and 1:2 solutions showed just an efflorescence transition during the first dehydration process and no efflorescence and deliquescence transition during the hygroscopic cycles, respectively. The observed different hygroscopic behavior was due to the different contents of NaCl, MA, and monosodium malonate in the aerosols, which were monitored real-time by in situ RMS.

Combined use of quantitative ED-EPMA, Raman microspectrometry, and ATR-FTIR imaging techniques for the analysis of individual particles.

In this work, quantitative energy-dispersive electron probe X-ray microanalysis (ED-EPMA) (called low-Z particle EPMA), Raman microspectrometry (RMS), and attenuated total reflectance Fourier transform infrared spectroscopic (ATR-FTIR) imaging were applied in combination for the analysis of the same individual airborne particles for the first time. After examining individual particles of micrometer size by low-Z particle EPMA, consecutive examinations by RMS and ATR-FTIR imaging of the same individual particles were then performed. The relocation of the same particles on Al or Ag foils was successfully carried out among the three standalone instruments for several standard samples and an indoor airborne particle sample, resulting in the successful acquisition of quality spectral data from the three single-particle analytical techniques. The combined application of the three techniques to several different standard particles confirmed that those techniques provided consistent and complementary chemical composition information on the same individual particles. Further, it was clearly demonstrated that the three different types of spectral and imaging data from the same individual particles in an indoor aerosol sample provided richer information on physicochemical characteristics of the particle ensemble than that obtainable by the combined use of two single-particle analytical techniques.

Influence of collecting substrates on the characterization of hygroscopic properties of inorganic aerosol particles.

The influence of six collecting substrates with different physical properties on the hygroscopicity measurement of inorganic aerosol particle surrogates and the potential applications of these substrates were examined experimentally. Laboratory-generated single salt particles, such as NaCl, KCl, and (NH4)2SO4, 1-5 µm in size, were deposited on transmission electron microscopy grids (TEM grids), parafilm-M, Al foil, Ag foil, silicon wafer, and cover glass. The particle hygroscopic properties were examined by optical microscopy. Contact angle measurements showed that parafilm-M is hydrophobic, and cover glass, silicon wafer, Al foil, and Ag foil substrates are hydrophilic. The observed deliquescence relative humidity (DRH) values for NaCl, KCl, and (NH4)2SO4 on the TEM grids and parafilm-M substrates agreed well with the literature values, whereas the DRHs obtained on the hydrophilic substrates were consistently ∼1-2% lower, compared to those on the hydrophobic substrates. The water layer adsorbed on the salt crystals prior to deliquescence increases the Gibb's free energy of the salt crystal-substrate system compared to the free energy of the salt droplet-substrate system, which in turn reduces the DRHs. The hydrophilic nature of the substrate does not affect the measured efflorescence RH (ERH) values. However, the Cl(-) or SO4(2-) ions in aqueous salt droplets seem to have reacted with Ag foil to form AgCl or Ag2SO4, respectively, which in turn acts as seeds for the heterogeneous nucleation of the original salts, leading to higher ERHs. The TEM grids were found to be most suitable for the hygroscopic measurements of individual inorganic aerosol particles by optical microscopy and when multiple analytical techniques, such as scanning electron microscopy-energy dispersive X-ray spectroscopy, TEM-EDX, and/or Raman microspectrometry, are applied to the same individual particles.

An investigation into the relationship between the major chemical components of particulate matter in urban air.

Particulate matter (PM) generally comprises such chemical components as inorganic ions, organic carbon (OC), elemental carbon (EC), and metals. In terms of environmental studies, these major chemical components of particulate matter (MCP) are important in understanding PM distribution, behaviors and source apportionment. In this study, the MCP fractions of total suspended particles (TSP) were measured at an urban residential area in Seoul, Korea from February to December in 2009. The behavior of each individual MCP was studied in order to explain their relationship to environmental conditions and sources. The MCP measured during this study period was able to account between 54% (spring) to 67% (fall) of total TSP composition. During the study period, it was found that the TSP sampled comprised mostly: anions, OC, cations, EC, and metals in decreasing order of abundance. Although such relative ordering seems to remain fairly constant over time, the relative balance of this relationship may be altered by variations in environmental conditions.

Iron speciation of airborne subway particles by the combined use of energy dispersive electron probe X-ray microanalysis and Raman microspectrometry.

Quantitative energy-dispersive electron probe X-ray microanalysis (ED-EPMA), known as low-Z particle EPMA, and Raman microspectrometry (RMS) were applied in combination for an analysis of the iron species in airborne PM10 particles collected in underground subway tunnels. Iron species have been reported to be a major chemical species in underground subway particles generated mainly from mechanical wear and friction processes. In particular, iron-containing particles in subway tunnels are expected to be generated with minimal outdoor influence on the particle composition. Because iron-containing particles have different toxicity and magnetic properties depending on their oxidation states, it is important to determine the iron species of underground subway particles in the context of both indoor public health and control measures. A recently developed analytical methodology, i.e., the combined use of low-Z particle EPMA and RMS, was used to identify the chemical species of the same individual subway particles on a single particle basis, and the bulk iron compositions of airborne subway particles were also analyzed by X-ray diffraction. The majority of airborne subway particles collected in the underground tunnels were found to be magnetite, hematite, and iron metal. All the particles collected in the tunnels of underground subway stations were attracted to permanent magnets due mainly to the almost ubiquitous ferrimagnetic magnetite, indicating that airborne subway particles can be removed using magnets as a control measure.

Investigation of the chemical mixing state of individual Asian dust particles by the combined use of electron probe X-ray microanalysis and Raman microspectrometry.

In this work, quantitative electron probe X-ray microanalysis (EPMA) and Raman microspectrometry (RMS) were applied in combination for the first time to characterize the complex internal structure and physicochemical properties of the same ensemble of Asian dust particles. The analytical methodology to obtain the chemical composition, mixing state, and spatial distribution of chemical species within single particles through the combined use of the two techniques is described. Asian dust aerosol particles collected in Incheon, Korea, during a moderate dust storm event were examined to assess the applicability of the methodology to resolve internal mixtures within single particles. Among 92 individual analyzed particles, EPMA and RMS identified 53% of the particles to be internally mixed with two or more chemical species. Information on the spatial distribution of chemical compounds within internally mixed individual particles can be useful for deciphering the particle aging mechanisms and sources. This study demonstrates that the characterization of individual particles, including chemical speciation and mixing state analysis, can be performed more in detail using EPMA and RMS in combination than with the two single-particle techniques alone.

Chemical speciation of size-segregated floor dusts and airborne magnetic particles collected at underground subway stations in Seoul, Korea.

Previous studies have reported the major chemical species of underground subway particles to be Fe-containing species that are generated from wear and friction processes at rail-wheel-brake and catenaries-pantographs interfaces. To examine chemical composition of Fe-containing particles in more details, floor dusts were collected at five sampling locations of an underground subway station. Size-segregated floor dusts were separated into magnetic and non-magnetic fractions using a permanent magnet. Using X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDX), iron metal, which is relatively harmless, was found to be the dominating chemical species in the floor dusts of the <25 µm size fractions with minor fractions of Mg, Al, Si, Ca, S, and C. From SEM analysis, the floor dusts of the <25 µm size fractions collected on railroad ties appeared to be smaller than 10 µm, indicating that their characteristics should somewhat reflect the characteristics of airborne particles in the tunnel and the platform. As most floor dusts are magnetic, PM levels at underground subway stations can be controlled by removing magnetic indoor particles using magnets. In addition, airborne subway particles, most of which were smaller than 10 µm, were collected using permanent magnets at two underground subway stations, namely Jegi and Yangjae stations, in Seoul, Korea. XRD and SEM/EDX analyses showed that most of the magnetic aerosol particles collected at Jegi station was iron metal, whereas those at Yangjae station contained a small amount of Fe mixed with Na, Mg, Al, Si, S, Ca, and C. The difference in composition of the Fe-containing particles between the two subway stations was attributed to the different ballast tracks used.

Nondestructive characterization of municipal-solid-waste-contaminated surface soil by energy-dispersive X-ray fluorescence and low-Z (atomic number) particle electron probe X-ray microanalysis.

The long-term environmental impact of municipal solid waste (MSW) landfilling is still under investigation due to the lack of detailed characterization studies. A MSW landfill site, popularly known as Dhapa, in the eastern fringe of the metropolis of Kolkata, India, is the subject of present study. A vast area of Dhapa, adjoining the current core MSW dump site and evolving from the raw MSW dumping in the past, is presently used for the cultivation of vegetables. The inorganic chemical characteristics of the MSW-contaminated Dhapa surface soil (covering a 2-km stretch of the area) along with a natural composite (geogenic) soil sample (from a small countryside farm), for comparison, were investigated using two complementary nondestructive analytical techniques, energy-dispersive X-ray fluorescence (EDXRF) for bulk analysis and low-Z (atomic number) particle electron probe X-ray microanalysis (low-Z particle EPMA) for single-particle analysis. The bulk concentrations of K, Rb, and Zr remain almost unchanged in all the soil samples. The Dhapa soil is found to be polluted with heavy metals such as Cu, Zn, and Pb (highly elevated) and Ti, Cr, Mn, Fe, Ni, and Sr (moderately elevated), compared to the natural countryside soil. These high bulk concentration levels of heavy metals were compared with the Ecological Soil Screening Levels for these elements (U.S. Environment Protection Agency) to assess the potential risk on the immediate biotic environment. Low-Z particle EPMA results showed that the aluminosilicate-containing particles were the most abundant, followed by SiO2, CaCO3-containing, and carbonaceous particles in the Dhapa samples, whereas in the countryside sample only aluminosilicate-containing and SiO2 particles were observed. The mineral particles encountered in the countryside sample are solely of geogenic origin, whereas those from the Dhapa samples seem to have evolved from a mixture of raw dumped MSW, urban dust, and other contributing factors such as wind, precipitation, weather patterns, farming, and water logging, resulting in their diverse chemical compositions and the abundant observation of carbonaceous species. Particles containing C and P were more abundant in the Dhapa samples than in the countryside soil sample, suggesting that MSW-contaminated soils are more fertile. However, the levels of particles containing potentially toxic heavy metals such as Cr, Mn, Ni, Cu, Zn, and/or Pb in the Dhapa samples were significant, corroborated by their high bulk concentration levels (EDXRF), causing deep concern for the immediate environment and contamination of the food chain through food crops.

Single-particle characterization of atmospheric aerosols collected at Gosan, Korea, during the Asian Pacific Regional Aerosol Characterization Experiment field campaign using low-Z (atomic number) particle electron probe X-ray microanalysis.

A quantitative energy-dispersive electron probe X-ray microanalysis (ED-EPMA), namely low-Z (atomic number) particle EPMA, was used to characterize the chemical compositions of the individual aerosol particles collected at the Gosan supersite, Jeju Island, Korea, as a part of the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia). On 4-10 April 2001 just before a severe dust storm arrived, seven sets of aerosol samples were obtained by a seven-stage May cascade impactor with a flow rate of 20 L/min. Overall 11,200 particles on stages 1-6 with cutoff diameters of 16, 8, 4, 2, 1, and 0.5 microm, respectively, were examined and classified based on their secondary electron images and X-ray spectra. In general, sea salt particles were the most frequently encountered, followed by mineral dust, organic carbon (OC)-like, (NH4)2SO4/NH4HSO4-containing, elemental carbon (EC)-like, Fe-rich, and K-rich particles. Sea salt and mineral dust particles had a higher relative abundance on stages 1-5, whereas OC-like, (NH4)2SO4/NH4HSO4-containing, Fe-rich, and K-rich particles were relatively abundant on stage 6. The analysis on relative number abundances of various particle types combined with 72-hr backward air mass trajectories indicated that a lot of reacted sea salt and reacted mineral dust (with airborne NOx and SO2 or their acidic products) and OC-like particles were carried by the air masses passing over the Yellow Sea (for sample "10 April") and many NH4HSO4/ (NH4)2SO4-containing particles were carried by the air masses passing over the Sea of Japan and Korea Strait (for samples "4-9 April"). It was concluded that the atmosphere over Jeju Island was influenced by anthropogenic SO2 and NOx, organic compounds, and secondary aerosols when Asian dust was absent.

Single-particle mineralogy of Chinese soil particles by the combined use of low-Z particle electron probe X-ray microanalysis and attenuated total reflectance-FT-IR imaging techniques.

Our previous work on the speciation of individual mineral particles of micrometer size by the combined use of attenuated total reflectance FT-IR (ATR-FT-IR) imaging and a quantitative energy-dispersive electron probe X-ray microanalysis technique (EPMA), low-Z particle EPMA, demonstrated that the combined use of these two techniques is a powerful approach for looking at the single-particle mineralogy of externally heterogeneous minerals. In this work, this analytical methodology was applied to characterize six soil samples collected at arid areas in China, in order to identify mineral types present in the samples. The six soil samples were collected from two types of soil, i.e., loess and desert soils, for which overall 665 particles were analyzed on a single particle basis. The six soil samples have different mineralogical characteristics, which were clearly differentiated in this work. As this analytical methodology provides complementary information, the ATR-FT-IR imaging on mineral types, and low-Z particle EPMA on the morphology and elemental concentrations, on the same individual particles, more detailed information can be obtained using this approach than when either low-Z particle EPMA or ATR-FT-IR imaging techniques are used alone, which has a great potential for the characterization of Asian dust and mineral dust particles.

Single-particle characterization of summertime Antarctic aerosols collected at King George Island using quantitative energy-dispersive electron probe X-ray microanalysis and attenuated total reflection Fourier transform-infrared imaging techniques.

Single-particle characterization of Antarctic aerosols was performed to investigate the impact of marine biogenic sulfur species on the chemical compositions of sea-salt aerosols in the polar atmosphere. Quantitative energy-dispersive electron probe X-ray microanalysis was used to characterize 2900 individual particles in 10 sets of aerosol samples collected between March 12 and 16, 2009 at King Sejong Station, a Korean scientific research station located at King George Island in the Antarctic. Two size modes of particles, i.e., PM(2.5-10) and PM(1.0-2.5), were analyzed, and four types of particles were identified, with sulfur-containing sea-salt particles being the most abundant, followed by genuine sea-salt particles without sulfur species, iron-containing particles, and other species including CaCO(3)/CaMg(CO(3))(2), organic carbon, and aluminosilicates. When a sulfur-containing sea-salt particle showed an atomic concentration ratio of sulfur to sodium of >0.083 (seawater ratio), it is regarded as containing nonsea-salt sulfate (nss-SO(4)(2-)) and/or methanesulfonate (CH(3)SO(3)(-)), which was supported by attenuated total reflection Fourier transform-infrared imaging measurements. These internal mixture particles of sea-salt/CH(3)SO(3)(-)/SO(4)(2-) were very frequently encountered. As nitrate-containing particles were not encountered, and the air-masses for all of the samples originated from the Pacific Ocean (based on 5-day backward trajectories), the oxidation of dimethylsulfide (DMS) emitted from phytoplanktons in the ocean is most likely to be responsible for the formation of the mixed sea-salt/CH(3)SO(3)(-)/SO(4)(2-) particles.