Carbonaceous Components Research Articles

Regional haze formation enhanced the atmospheric pollution levels in the Yangtze River Delta region, China: Implications for anthropogenic sources and secondary aerosol formation

High-time-resolution (3-hour) PM2.5 samples were collected simultaneously from the rural and urban areas in the Yangtze River Delta region during winter. The aerosol samples were analyzed for carbonaceous components, organic tracers, water-soluble inorganic ions and stable carbon (δ13C) and nitrogen (δ15N) isotopic compositions of total carbon and total nitrogen. The values of PM2.5 and secondary organic carbon (SOC) for both sampling sites were observed 2 times higher in haze events compare to those in clear days, implying severe pollution occurred by photochemical oxidation during haze periods. The PM mass of rural samples showed similar temporal trend and significant correlation with the urban PM, reflecting pollution sources or their formation process are most likely identical. Diurnal variations of PM2.5 and carbonaceous components revealed that pollution levels increased at daytime due to the photochemical oxidation. In addition, SOC and OC were influenced by the relative humidity (RH%) and temperature (T °C), indicating that such meteorological factors play important roles in the occurrence of regional air pollution. The concentrations of levoglucosan, polycyclic aromatic hydrocarbons, hopanes, and n-alkanes were 625 ± 456 and 519 ± 301 ng m−3, 32.6 ± 24.7 and 28.7 ± 20.1 ng m−3, 1.83 ± 1.51 and 1.26 ± 1.34 ng m−3, and 302 ± 206 and 169 ± 131 ng m−3 for rural and urban samples, respectively. Levoglucosan is the most abundant organic compounds, exhibited 2–3 times higher in haze than clear days, suggesting biomass burning (BB) emission substantially affects the haze pollution in winter. Furthermore, NO3− was the dominant ionic species followed by SO42−, NH4+, Cl− and other minor species for both sites. The δ13C and δ15N values demonstrate that anthropogenic activities such as fossil fuel combustion and BB are the major sources for carbonaceous and nitrogenous aerosols. This study implies that both the regional anthropogenic emissions and meteorological conditions influenced the regional haze formation, leading enhancement of pollution levels in eastern China during winter.

Investigation of Primary and Secondary Particulate Brown Carbon in Two Chinese Cities of Xi'an and Hong Kong in Wintertime.

Brown carbon (BrC), an aerosol carbonaceous matter component, impacts atmospheric radiation and global climate because of its absorption in the near-ultraviolet-visible region. Simultaneous air sampling was conducted in two megacities of Xi'an (northern) and Hong Kong (southern) in China in winter of 2016-2017. The aim of this study is to determine and characterize the BrC compounds in collected filter samples. Characteristic absorption peaks corresponding to aromatic C-C stretching bands, organo-nitrates, and C═O functional groups were seen in spectra of Xi'an samples, suggesting that the BrC was derived from freshly smoldering biomass and coal combustion as well as aqueous formation of anthropogenic secondary organic carbon. In Hong Kong, the light absorption of secondary BrC accounted for 76% of the total absorbances of BrC. The high abundance of strong C═O groups, biogenic volatile organic compounds (BVOCs) and atmospheric oxidants suggest secondary BrC was likely formed from photochemical oxidation of BVOCs in Hong Kong. Several representative BrC molecular markers were detected using Fourier transform ion cyclotron resonance mass spectrometry and their absorption properties were simulated by quantum chemistry. The results demonstrate that light absorption capacities of secondary anthropogenic BrC with nitro-functional groups were stronger than those of biogenic secondary BrC and anthropogenic primary BrC.

Effect of Carbonaceous Components on Tribological Properties of Copper-Free NAO Friction Material.

Copper helps to accelerate heat transfer during the braking process, allowing the brake materials to produce a stable coefficient of friction (COF), which in turn reduces wear loss and braking noise. However, its properties are also quite harmful to aquatic organisms. Finding a suitable replacement that fits all functions of copper for brake materials is not an easy feat. In this paper, six different carbonaceous components (coke, carbon black, carbon fiber, artificial graphite, natural graphite and expanded graphite) were substituted for copper in non-asbestos organic (NAO) friction materials. The hardness, thermal conductivity and tribological behaviors of these copper-free NAO friction materials were examined. Experimental results indicate that carbonaceous components improve lubrication and assist the friction composites with generating friction layers on the worn surface. Specimens containing coke, carbon black or carbon fiber exhibit broken friction layers, whereas specimens containing artificial graphite, natural graphite or expanded graphite exhibit quite adherent and smooth friction layers. Among all the copper-free carbon containing specimens, the specimen containing expanded graphite appears to be the best choice. It has the highest thermal conductivity, a relatively low wear loss and a relatively high and stable COF.

Sub-type source profiles of fine particles for fugitive dust and accumulative health risks of heavy metals: a case study in a fast-developing city of China.

Sub-type source profiles for atmospheric fine particle (PM2.5) were still scare in China, which limited the accurate source identification of it. Fugitive dust (including road dust, soil dust, resuspended dust, and construction dust, etc.) was one type of the most important contributors to PM2.5 and its associated toxic metals held potential threaten to human health. The chemical compositions, sources, and health risks of sub-type fugitive dust deserved an investigation for further accurate control of particles and alleviating human health risks. A total of sixty-five fugitive dust samples were collected in Suzhou, a fast-developing city in southern China, including eleven sub-types of road dust (overpass, main street, collector street, and ordinary street), soil dust (farmland and tree lawn), resuspended dust (site types were corresponding to those of road dust), and construction dust (large construction sites). Chemical analysis of water-soluble ions, elements, and carbonaceous components was carried out to establish the sub-type source profiles of PM2.5 for fugitive dust. Results showed that crustal elements were the most abundant components of fugitive dust, and soil dust was less polluted by anthropogenic activities. High contents of OC and low contents of EC were found in all the eleven types of dust. Equivalent ratios of anions and cations indicated that the fugitive dust was obviously alkaline. The contents of OC and EC in the four types of road dust were higher than those in other types of dust, while there existed differences among the sub-types of road dust. The NO3-/SO42- ratios (0.03-0.09) implied that coal-burning and motor vehicle emission co-existed in Suzhou. Coefficient divergence (CD) values of eleven sub-type source profiles showed that there were certain differences among them, which suggested the possibility of sub-type source identification. Cluster analysis indicated the heavy metals in fugitive dust were mainly from crustal materials, metallurgical manufacturing, vehicle emissions, and industrial activities. The enrichment degree of heavy metals for the four types of road dust was also inconsistent. Heavy metals in road dust and soil dust posed a non-carcinogenic risk to children through direct ingestion, and the non-carcinogenic risk of direct intake of heavy metals was much higher than that of respiratory and skin contact. It was found that the accumulative health risks of heavy metals were higher in densely populated areas, traffic intensive areas, and industrial areas through the spatial analysis. This study firstly discussed the chemical compositions of PM2.5 for eleven sub-types of fugitive dust in a Chinese city and assessed the accumulative health risks of heavy metals, which could be a demonstration for further related researches.

Light absorption properties of elemental carbon (EC) and water-soluble brown carbon (WS–BrC) in the Kathmandu Valley, Nepal: A 5-year study

This study presents a comprehensive analysis of organic carbon (OC), elemental carbon (EC), and particularly the light absorption characteristics of EC and water-soluble brown carbon (WS–BrC) in total suspended particles in the Kathmandu Valley from April 2013 to January 2018. The mean OC, EC, and water-soluble organic carbon (WSOC) concentrations were 34.8 ± 27.1, 9.9 ± 5.8, and 17.4 ± 12.5 μg m−3, respectively. A clear seasonal variation was observed for all carbonaceous components with higher concentrations occurring during colder months and lower concentrations in the monsoon season. The relatively low OC/EC ratio (3.6 ± 2.0) indicates fossil fuel combustion as the primary source of carbonaceous components. The optical attenuation (ATN) at 632 nm was significantly connected with EC loading (ECS) below 15 μg cm−2 but ceased as ECS increased, reflecting the increased influence of the shadowing effect. The derived average mass absorption cross-section of EC (MACEC) (7.0 ± 4.2 m2 g−1) is comparable to that of freshly emitted EC particles, further attesting that EC was mainly produced from local sources with minimal atmospheric aging processes. Relatively intensive coating with organic aerosols and/or salts (e.g., sulfate, nitrate) was probably the reason for the slightly higher MACEC during the monsoon season, whereas increased biomass burning was a major factor leading to lower MACEC in other seasons. The average MACWS-BrC at 365 nm was 1.4 ± 0.3 m2 g−1 with minimal seasonal variations. In contrast to MACEC, biomass burning was the main reason for a higher MACWS-BrC in the non-monsoon season. The relative light absorption contribution of WS-BrC to EC was 9.9% over the 300–700 nm wavelength range, with a slightly higher ratio (13.6%) in the pre-monsoon season. Therefore, both EC and WS-BrC should be considered in the study of optical properties and radiative forcing of carbonaceous aerosols in this region.

Analysis of Water Soluble Organic Aerosol in Spring PM2.5 with Soot Particle Aerosol Mass Spectrometry (SP-AMS)

To investigate the chemical composition and pollution characteristics of spring fine particles (PM2.5) in Changzhou, a total of 84 PM2.5 samples were collected from March 1st to May 30th, 2017. We measured and analyzed conventional components, such as water-soluble ions (WSIIs) and carbonaceous components (OC and EC). The water-soluble organic aerosol (WSOA) was also analyzed by an aerodyne soot particle aerosol mass spectrometer (SP-AMS). During the sampling period, the average daily PM2.5 concentration was 101.97 μg·m-3, with more than 73.8% sampling days exceeding the Target-2 standard of the national ambient air quality standard of China. The air quality during the sampling period was dominated by light, moderate, and heavy pollution, accounting for 39.3%, 21.4%, and 13.1% of the total days, respectively. The total WSIIs accounted for 39.86% of PM2.5 mass, of which secondary ions (SO42-, NH4+, and NO3-) accounted for 81.85% of the total WSIIs. The slope of the linear fitted line of the anion and cation charge balance (AE/CE) was greater than 1 (1.09), which indicated that PM2.5 was weakly acidic. The average OC/EC ratio was 2.53, indicating that PM2.5 was influenced by the secondary conversion. WSOA included CxHy+(32.1%), CxHyO+(30.4%), CxHyO2+(25.4%), and HyO+(4.7%) identified by SP-AMS. The average oxygen-to-carbon (O/C), hydrogen-to-carbon (H/C), nitrogen-to-carbon (N/C), and organic matter-to-organic carbon (OM/OC) ratios of the WSOA were 0.72, 1.53, 0.04, and 2.15, respectively. Higher O/C indicated higher contributions from secondary photochemical reaction conversion in spring. Positive matrix factorization (PMF) analysis for AMS mass spectra of WSOA identified three sources, namely hydrocarbon-like (HOA), semi-volatile oxygenated OA (SVOOA)-biomass burning OA (BBOA), and low-volatility oxygenated OA (LVOOA), which on average accounted for 18.4%, 34.1%, and 47.4% of the total WSOA, respectively.

Carbonaceous Aerosol Emitted from Biofuel Household Stove Combustion in South China

Near-source measurements of smoke emissions from household stove combustion in a rural area of South China were conducted with 7 typical biomass fuels. Particulate matter samples (both PM10 and PM2.5) were analyzed for their carbonaceous components, including organic and elemental carbon (OC, EC) as well as levoglucosan (molecular tracer of biomass burning), employing thermal-optical and GC-MS analysis. The OC and EC content in PM2.5 and PM10 smoke particles derived from the various types of vegetation showed different patterns with the smallest values observed for straw type fuels. The OC/EC ratios in PM2.5 and PM10 showed an order of straw > hardwood > bamboo > softwood. Mass concentrations of particulate matter emitted from rice straw burning were highest with 12.23 ± 0.87 mg/m3 (PM10) and 9.31 ± 0.81 mg/m3 (PM2.5), while the mass ratios (LG/PM and OC/PM) were lowest among the 7 fuels, indicating that particle emissions from straw burning were higher than those from woody fuels, using similar burning conditions. The levoglucosan emission ratios were rather high and this single most abundant organic species was mainly present in the fine particle mode. Linear correlation analysis showed a strong relationship between levoglucosan and EC emissions.

Towards Advanced Sodium-Ion Batteries: Green, Low-Cost and High-Capacity Anode Compartment Encompassing Phosphorus/Carbon Nanocomposite as the Active Material and Aluminum as the Current Collector

Sodium-ion batteries (SIBs) are promising alternative to Lithium-ion batteries for massive stationary energy storage. To improve energy density, however, more performing active materials are needed. In order to allow sustainable scale-up, it is also mandatory to develop green products and processes. Herein, we report on anodes of phosphorus/carbon (P/C) nanocomposites prepared via High Energy Ball Milling (HEBM), a simple, powerful and easily scalable synthesis technique. The electrodes were prepared under oxygen-free atmosphere, using water as solvent, which enabled the use of aluminum (instead of copper) as current collector, implying significant cost reduction. The P/C nanocomposite obtained after 54 h HEBM resulted in excellent cycling stability, delivering very high specific capacity (2200 mAh g−1, C/20) and showing good capacity retention after 120 cycles. A careful structural analysis (XRD, FESEM-EDS, XPS), revealed that long milling times strongly increased cycling stability due to: (i) significant decrease of P particle size inside the matrix and deep composite amorphization, which alleviates the buffering dimensional issues typical of black phosphorus; (ii) presence of defects in the carbonaceous component, which allows easier Na+ insertion into the anode. Our results show that P/C nanocomposites are very promising anode materials for SIBs, paving the way for further exploitation of nano-architectures in SIBs technology.

The Role of PM2.5 Chemical Composition and Meteorology during High Pollution Periods at a Suburban Background Station in Southern Poland

This study conducted measurements of PM2.5 (particulate matter with a diameter ≤ 2.5 µm) in Racibórz, Poland, during 2018. Samples were collected daily and analyzed for their chemical composition, specifically, the carbonaceous (elemental and organic carbon) and water-soluble ionic (Cl–, NO3–, SO42–, Na+, NH4+, K+, Ca2+ and Mg2+) components. Additionally, the secondary inorganic aerosol (SIA) as well as the secondary and primary organic carbon (SOC and POC, respectively) content was estimated. To identify the causes of elevated PM2.5 concentrations, the contributions of these chemical species were further investigated, and the role of meteorological factors was also examined. During the measurement period, PM2.5 concentrations exceeding 50 µg m–3 were recorded on 38 days, and 7 pollution episodes were detected. Such events, however, were observed only in the heating season, when stable meteorological conditions (low air temperatures, weak winds, high relative humidity and lack of precipitation) and increased emissions of PM and its precursors from anthropogenic sources favored the accumulation of pollutants. The PM2.5 was dominated by carbonaceous aerosol, especially POC, although the SOC rose significantly during high pollution periods. Furthermore, the fraction of SIA clearly decreased as the concentration of PM2.5 increased, and its variability was greatly affected by regional and/or long-range transport events. Our results can help guide the development of effective strategies for reducing air pollution from fine particulate matter. Such control measures are particularly important in Poland, where PM2.5 concentrations remain high compared to many European countries.

Filterable PM2.5, Metallic Elements, and Organic Carbon Emissions from the Exhausts of Diesel Vehicles

ABSTRACT Urban air pollution in the form of fine particulate matter (PM2.5) constitutes substantial health risks to human via inhalation. To determine the inhalation risks of PM2.5 containing metallic elements, we characterized and quantified PM2.5 emissions from the exhaust of 15 diesel vehicles having accrued mileages ranging from 28,306 to 883,374 km (average of 525,854 km). These vehicles originated from several manufacturers and covered model years from 1988 to 2005. The concentrations of metallic elements (Fe, Zn, Mg, K, Ca, Al, and Cr) were studied with the help of Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The results demonstrate that the metallic element composition in exhaust PM2.5 was in descending order as follows: Ca, Zn, Al, K, Fe, and Cr. The exhaust components containing PM2.5 and other chemical compositions were obtained based on carbonaceous materials (total carbon -TC, organic carbon - OC and elemental carbon - EC). Our results demonstrate that elemental carbon (EC) and organic carbon (OC) were the key concentrations of carbonaceous components: EC accounted for 2051 µg m-3 of PM2.5, while the OC fraction accounted for 1410 μg m-3, and TC accounted for 3461 µg m-3, respectively. The results have revealed Ca had the highest EFs among all the investigated atmospheric metallic elements, which ranged between 45.3 and 259 μg/L-fuel (with an average of 132 μg/L-fuel). Zn and Cr had the lowest EFs, accounting for a mean average of 13.1 μg/L-fuel and 1.91 μg/L-fuel, respectively. The concentrations and EFs of metallic elements in PM2.5 exhaust also were studied in relationship to atmospheric PM2.5 composition. These results will help further an understanding of how PM2.5 emissions from diesel vehicles contribute to metallic element concentrations in the natural environment and their potential negative effects.

Source Apportionment of PM2.5 and of its Oxidative Potential in an Industrial Suburban Site in South Italy

Some studies suggested a role of the atmospheric particulate matter (PM) and of its oxidative potential (OP) in determining adverse health effects. Several works have focused on characterisation of source contributions to PM OP, mainly using three approaches: correlation between OP and chemical markers of specific sources; use of OP as input variable in source apportionment with receptor models; and multi-linear regression (MLR) between OP and source contributions to PM obtained from receptor models. Up to now, comparison of results obtained with different approaches on the same dataset is scarce. This work aims to perform a OP study of PM2.5 collected in an industrial site, located near a biogas production and combustion plant (in southern Italy), comparing different approaches to investigate the contributions of the different sources to OP. The PM2.5 samples were analysed for determining ions, metals, carbonaceous components, and OP activity with the DTT (dithiotreitol) assay. Results showed that OP normalised in volume (DTTV) is correlated with carbonaceous components and some ions (NO3−, and Ca2+) indicating that PM of combustion, secondary, and crustal origin could contribute to the OP activity. The source apportionment, done with the Environmental Protection Agency (EPA)—Positive Matrix Factorization (PMF5.0) model, identified six sources: secondary sulphate; biomass burning; industrial emissions; crustal; vehicle traffic and secondary nitrate; and sea spray. A MLR analysis between the source’s daily contributions and the daily DTTV values showed a reasonable agreement of the two approaches (PMF and MLR), identifying the biomass burning and the vehicle traffic and secondary nitrate as the main sources contributing to DTTV activity.

Formation and composition of the UTLS aerosol

Stratospheric aerosol has long been seen as a pure mixture of sulfuric acid and water. Recent measurements, however, found a considerable carbonaceous fraction extending at least 8 km into the stratosphere. This fraction affects the aerosol optical depth (AOD) and the radiative properties, and hence the radiative forcing and climate impact of the stratospheric aerosol. Here we present an investigation based on a decade (2005–2014) of airborne aerosol sampling at 9–12 km altitude in the tropics and the northern hemisphere (NH) aboard the IAGOS-CARIBIC passenger aircraft. We find that the chemical composition of tropospheric aerosol in the tropics differs markedly from that at NH midlatitudes, and, that the carbonaceous stratospheric aerosol is oxygen-poor compared to the tropospheric aerosol. Furthermore, the carbonaceous and sulfurous components of the aerosol in the lowermost stratosphere (LMS) show strong increases in concentration connected with springtime subsidence from overlying stratospheric layers. The LMS concentrations significantly exceed those in the troposphere, thus clearly indicating a stratospheric production of not only the well-established sulfurous aerosol, but also a considerable but less understood carbonaceous component.

A carbonaceous chondrite and cometary origin for icy moons of Jupiter and Saturn

The inner structure of icy moons comprises ices, liquid water, a silicate rocky core and sometimes an inner metallic core depending on thermal evolution and differentiation. Mineralogy and density models for the silicate part of the icy satellites cores were assessed assuming a carbonaceous chondritic (CI) bulk composition and using a free-energy minimization code and experiments. Densities of other components, solid and liquid sulfides, carbonaceous matter, were evaluated from available equations of state. Model densities for silicates are larger than assessed from magnesian terrestrial minerals, by 200 to 600 kg.m−3 for the hydrated silicates, and 300 to 500 kg.m−3 for the dry silicates, due to the high iron bulk concentration in CI. The stability of Na-phlogopite in the silicate fraction up to 1300 K favors the trapping of most 40K in the rocky/carbonaceous cores with important consequences for modeling of the thermal evolution of icy satellites. We find that CI density models of icy satellite cores taking into account only the silicate and metal/sulfide fraction cannot account for the observed densities and reduced moment of inertia of Titan and Ganymede without adding a lower density component. We propose that this low-density component is carbonaceous matter derived from insoluble organic matter, in proportion of ∼30-40% in volume and 15-20% in mass. This proportion is compatible with contributions from CI and comets, making these primitive bodies including their carbonaceous matter component likely precursors of icy moons, and potentially of most of the objects formed behind the snow line of the solar system.

Review of PM Oxidative Potential Measured with Acellular Assays in Urban and Rural Sites across Italy

This work is an overview of the oxidative potential (OP) values up to date measured in Italy, with the aim to provide a picture of the spatial and seasonal variability of OP in the various geographical areas across Italy. The summarized works used the common acellular assays-based dithiothreitol (OPDTT), ascorbic acid (OPAA), glutathione (OPGSH), and 2′,7′-dichlorodfluorescein (OPDCFH) assays. The paper describes the association of OP responses with PM chemical composition, the sensitivity of various acellular OP assays to PM components and emission sources, and PM size distribution of the measured OP values. Our synthesis indicates that crustal and transition metals (e.g., Fe, Ni, Cu, Cr, Mn, Zn, and V), secondary ions and carbonaceous components (elemental carbon, EC, organic carbon, OC and water soluble carbon, WSOC) show significant correlations with OP across different urban and rural areas and size ranges. These chemical species are mainly associated with various PM sources, including residual/fuel oil combustion, traffic emissions, and secondary organic aerosol formation. Although the OP assays are sensitive to the same redox-active species, they differ in the association with PM chemical components. The DDT assay is mainly sensitive to the organic compounds that are mostly accumulated in the fine PM fraction, i.e., tracers of burning sources, and redox active organics associated with other markers of photochemical aging. In contrast, OPAA and OPGSH were mostly responsive to metals, mainly those related to non-exhaust traffic emissions (Cu, Zn, Cr, Fe, Ni, Mn, Sn, Cd, Pb), that are mainly accumulated in the coarse PM. Among the investigated sites, our synthesis shows larger OP values in Trentino region and the Po Valley, that may be explained by the high density of anthropogenic sources, and the orographic and meteorological characteristics, that favor the pollutants accumulation and aerosol photo-oxidative aging.

A characterization of HULIS-C and the oxidative potential of HULIS and HULIS-Fe(II) mixture in PM2.5 during hazy and non-hazy days in Shanghai

Humic-like substances (HULIS) were isolated from PM2.5 in Shanghai. The oxidative potential and the cytotoxicity of the isolated HULIS and its Fe(II) binary mixtures were evaluated by using cell-free Dithiothreitol (DTT) and cellular 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. Our data showed that HULIS-C contents in spring during hazy and non-hazy days were relatively higher than in winter. Cell-free DTT and bioassay (reactive oxygen species (ROS) and MTT) results showed that higher ROS values were released from individual HULIS or SRFA (Suwannee River Fulvic Acid) compounds than HULIS-Fe(II) complexes and Fe(II) alone. In addition, DTT and ROS correlation results were in line with each other and the oxidative potentials of HULIS and its binary mixtures were strongly inter-correlated with carbonaceous components (WSOC, OC) in PM2.5. Dose-dependent MTT results revealed that cell mortality positively correlated with the mass concentrations of HULIS (10–50 μg/ml). In the HULIS-Fe(II) system, the ROS generation ability depended on the mixing time of HULIS-C with Fe(II), thus suggesting that the organic-metal complexation time and the Fenton reaction induced by Fe (II) play a role in the cell mortality rate.

Emission Characteristics of Exhaust PM and Its Carbonaceous Components from China Ⅲ to China Ⅳ Diesel Vehicles in Shenyang

Diesel vehicles were the primary source of atmospheric particulate matter (PM) emitted by motor vehicles. To study the emission factors and carbon components of PM2.5 and PM10 from diesel vehicles in Shenyang, exhaust PM samples were collected from 15 diesel vehicles including small, medium, and large passenger vehicles, and light, medium, and heavy-duty trucks under China Ⅲ and China Ⅳ emission standards. This was undertaken using a dilution channel sampling system, and the carbon components were also analyzed. The results showed that the average distance-based PM2.5 and PM10 emission factors for diesel vehicles under China Ⅲ were (0.193±0.092) g·km-1 and (0.338±0.305) g·km-1, respectively, and for China Ⅳ were (0.085±0.038) g·km-1 and (0.100±0.042) g·km-1, respectively. This shows that the PM emission factors decreased significantly with the improvement of emission standards. Under the same emission standards, emission factors increased with the increase of vehicle passenger volume or cargo capacity. TC (total carbon) was the main component of the emissions from diesel vehicles. The mass fraction of TC under China Ⅳ (23%-48%) was significantly lower than under China Ⅲ (29%-70%). The mass fraction of elemental carbon (EC) for all types of diesel vehicles was greater than organic carbon (OC). The OC/EC value was 0.70±0.29, and the OC/EC value for diesel vehicles under China Ⅳ was lower than under China Ⅲ. The total mileage of passenger vehicles was significantly higher than that of trucks, resulting in higher fuel consumption. The mass fraction of OC and EC in passenger vehicles was higher than for trucks under the same emission standards. EC2 (elemental carbon which was measured at temperatures of 700℃) was the highest carbon content of diesel vehicles under China Ⅲ and China Ⅳ emission standards, which can be used in the identification of diesel vehicles in source apportionment studies.

Influence of High Relative Humidity on Secondary Organic Carbon: Observations at a Background Site in East China

To investigate the impacts of relative humidity (RH) on secondary organic aerosol (SOA) concentrations and chemical reactions, the carbonaceous aerosol components [i.e., organic carbon (OC) and element carbon (EC)] were quantified in daily PM2.5 samples collected at a background site in East China during summer 2015. Based on the method of EC-tracer, the concentration of secondary organic carbon (SOC) demonstrated an obvious negative relationship with RH higher than 60%. Moreover, the ratio of SOC/EC also exhibited obvious decreasing trends with increasing RH, indicating negative effects for chemical production of SOA under high RH conditions. Due to high RH, photochemistry was weakened, gaseous oxidant concentrations was lowered (e.g., significantly decreased O3 levels), and the production rates of SOA were relatively low. On the other hand, because of more water uptake under higher RH conditions, the aerosol droplet acidity was reduced and enhancement of SOA formation by acidity was accordingly absent. In addition, high RH also plays an important role in changing viscosity of pre-existing aerosol coatings, which can affect reactive uptake yield of SOA. Overall, the results from this study imply that SOA production may be more associated with photochemical processes, while aqueous-phase chemistry is not very important for some SOA formation in a moist ambient environment. In the ambient atmosphere, oxidant concentrations, reaction rates, airborne species, etc., are highly variable. How do these factors affect SOA yields under given ambient environment warrants further detailed investigations.

Real-Time Measurement of Airborne Carbon Nanotubes in Workplace Atmospheres.

With growing applications of carbon nanomaterials, there is a concern over health risks presented by inhalation of carbon nanotube (CNT) aerosol in workplace atmospheres. Current methods used for CNT aerosol measurement lack selectivity to specific form of carbonaceous component or allotrope of interest. Moreover, the detection limits of these methods are also inadequate for short-term monitoring. Here, we describe, for the first time, a near real-time, field-portable instrument for selective quantification of airborne CNT concentration. The approach uses an automated cyclical scheme involving collect-analyze-ablate steps to obtain continuous near real-time measurement using Raman spectroscopy. The method achieves significantly lower detection limits by employing corona-assisted particle microconcentration for efficient coupling with laser Raman spectroscopy. A combination of techniques involving (i) use of characteristic Raman peaks, (ii) distinct ratio of disordered and graphitic peaks, and (iii) principal component classification and regression is employed to identify and quantify the specific form of the aerosolized carbonaceous nanomaterial. We show that the approach is capable of selectively quantifying trace single-walled CNT in the presence of interfering agents such as diesel particulate matter. The detection limit of the method for the single-walled CNT studied in this work was 60 ng m-3, corresponding to a 10 min aerosol collection period, which is significantly lower than that for the NIOSH Method 5040 (∼0.15 μg m-3 for an 8-h collection on a 25 mm filter at 4 L min-1), a commonly used method for elemental carbon. We demonstrate the automated real-time capability of this field-portable method by continuously measuring a transient single-walled CNT aerosol.

Carbonaceous and water-soluble inorganic aerosols over a semi-arid location in north west India: Seasonal variations and source characteristics

This paper presents the seasonal features of major carbonaceous components in aerosols, their source characteristics and the role of meteorology in influencing the chemical characteristics of aerosols at a semi-arid location Udaipur (24.5°N; 73.6°E), India, based on the analysis of PM10 samples (N = 128) collected during 2010–14. The samples were analysed for OC (organic carbon), EC (elemental carbon), CC (carbonate carbon), WSOC (water-soluble OC), WSTN (water-soluble total nitrogen) and water-soluble inorganic ions. Primary and secondary OC (POC and SOC), water-insoluble OC (WIOC) and water-soluble organic nitrogen (WSON) were also estimated. The carbonaceous aerosols (TC) contributed to ~23% of PM10 loading. Both EC and OC mass loading showed high values during dry period (October to May) (OC = 26 ± 14 μg m−3, EC = 3.2 ± 2.2 μg m−3 with the PM10 mass loading of 140 ± 52 μg m−3) compared to wet period (June to September) (OC = 16 ± 10 μg m−3, EC = 1.4 ± 0.8 μg m−3 with the PM10 mass loading of 84 ± 43 μg m−3). While the crustal species, biomass tracers and anthropogenic species dominated during dry period, the sea salt species (Na+, Cl−, ss-SO4, ss-Mg, ss-Ca, ss-K) were comparatively higher in wet period. OC was found to be predominantly water-insoluble and secondary in nature. Local anthropogenic/natural emissions and marine transported aerosols (by south-westerlies) contributed during wet period, while dry period is influenced by transported anthropogenic aerosols from IGP and northern India (by north/north-easterlies) along with mineral aerosols from desert regions (by westerlies). Monthly average contribution of total carbonaceous aerosols (TCA = OM (organic matter) +EC + CC) varied from 20 to 42%, over a year while the water-soluble ionic fraction varied from 16 to 36% of the PM10 mass. The un-analysed part which is mostly mineral dust contributed 39–55%.

Size Distributions of Different Carbonaceous Components in Ambient Aerosols

It is important to obtain the size distribution of carbonaceous components in aerosols for studying the formation and transformation mechanisms and radiation characteristics of regional aerosols. However, only a few studies on the size distribution of aerosol carbonaceous fractions have been conducted in Beijing. In this study, a Micro-Orifice Uniform Deposit Impactor (MOUDI)-120 sampler was used to collect size-resolved aerosol samples in three seasons in Beijing, and the concentrations of different types of carbonaceous fractions were analyzed. Furthermore, the size distribution, characteristics, sources, and interrelationship of each carbonaceous component in different seasons and under different pollution levels were systematically studied. The results show that the carbonaceous components were concentrated mainly in fine particles, and the proportion of carbonaceous components in fine particles in autumn and winter was higher than that in summer. The carbonaceous components are distributed in two main modes:accumulation mode and coarse mode. Organic carbon fraction 1 (OC1) and OC2 were distributed mainly in the accumulated mode, with a higher proportion in the range of 0.056-0.56 μm, and OC3+OC4 was more abundant in the coarse mode. The concentration of Soot-elemental carbon (EC) was low but was highest in the 0.10-0.18 μm size range, which indicates that the EC emitted by high temperature combustion was distributed mainly in the ultra-fine particle size range. The Char-EC concentration was much higher, accounting for the majority of EC. The distribution appearances of the main carbonaceous components were essentially the same in the daytime and at night. Summer and winter were more conducive to the formation of SOC, and the OC/EC ratio was significantly higher than that in autumn. The OC/EC values varied greatly in different particle sizes because the water-soluble organic compounds (WSOC) were distributed mainly in the range of 0.056-0.10 μm, with significantly higher OC/EC values than other particle sizes. Sunlight and high temperature were beneficial to the oxidation of gaseous organic matter to SOC, resulting in the OC/EC ratio in summer in daytime to be significantly higher than that at night. Among the carbonaceous components, EC1 and OC1 had the strongest interrelation. In addition, EC1 also had stronger interrelation with potassium.