Elemental Carbon Mass Concentrations Research Articles

Evaluation of methods for characterizing the fine particulate matter emissions from aircraft and other diffusion flame combustion aerosol sources

The U. S. Environmental Protection Agency in collaboration with the U. S. Air Force Arnold Engineering Development Complex conducted the VAriable Response In Aircraft nvPM Testing (VARIAnT) 3 and 4 test campaigns to compare nonvolatile particulate matter (nvPM) emissions measurements from a variety of diffusion flame combustion aerosol sources (DFCASs), including a Cummins diesel engine, a diesel powered generator, two gas turbine start carts, a J85-GE-5 turbojet engine burning multiple fuels, and a Mini-CAST soot generator. The VARIAnT research program was devised to understand reported variability in the ARP6320A sampling system nvPM measurements. The VARIAnT research program has conducted four test campaigns to date with the VARIAnT 3 and 4 campaigns devoted to: (1) assessing the response of three different black carbon mass analyzers to particles of different size, morphology, and chemical composition; (2) characterizing the particles generated by 6 different combustion sources according to morphology, effective density, and chemical composition; and (3) assessing any significant difference between black carbon as determined by the 3 mass analyzers and the total PM determined via other techniques. Results from VARIAnT 3 and 4 campaigns revealed agreement of about 20% between the Micro-Soot Sensor, the Cavity Attenuated Phase Shift (CAPS PMSSA) monitor and the thermal-optical reference method for elemental carbon (EC) mass, independent of the calibration source used. For the LII-300, the measured mass concentrations in VARIAnT 3 fall within 18% and in VARIAnT 4 fall within 27% of the reference EC mass concentration when calibrated on a combustor rig in VARIAnT 3 and on an LGT-60 start cart in VARIAnT 4, respectively. It was also found that the three mass instrument types (MSS, CAPS PMSSA, and LII-300) can exhibit different BC to reference EC ratios depending on the emission source that appear to correlate to particle geometric mean mobility diameter, morphology, or some other parameter associated with particle geometric mean diameter (GMD) with the LII-300 showing a slightly stronger apparent trend with GMD. Systematic differences in LII-300 measured mass concentrations have been reduced by calibrating with a turbine combustion as a particle source (combustor or turbine engine). With respect to the particle size measurements, the sizing instruments (TSI SMPS, TSI EEPS, and Cambustion DMS 500) were found to be in general agreement in terms of size distributions and concentrations with some exceptions. Gravimetric measurements of the total aerosol mass produced by the various DFCAs differed from the reference EC, BC and integrated particle size distribution measured aerosol masses. The measurements of particle size distributions and single particle analysis performed using the miniSPLAT indicated the presence of larger particles (≳150 nm) having more compact morphologies, higher effective density, and a composition dominated by OC and containing ash. This increased large particle fraction is also associated with higher values of single scattering albedo measured by the CAPS PMSSA instrument and higher OC measurements. These measurements indicate gas turbine engine emissions can be a more heterogeneous mix of particle types beyond the original E−31 assumption that engine exit exhaust particles are mainly composed of black carbon.

Study of the effect of methanol/biodiesel fuel mixtures on the generation of soot particles and their oxidation reactivity

When diesel engines burn different fuels, the chemical composition of the emitted combustion particles changes, leading to changes in the oxidation characteristics of these particles and determining the regeneration strategy and service life of after treatment devices. In order to investigate the influence of methanol/biodiesel fuel mixtures on the chemical composition and oxidation activity of emitted soot matter, a test bench was built using a four-cylinder diesel engine, and soot matter in the exhaust was collected. Tests used mixed fuel with different methanol mixing ratios. By using a high-performance liquid chromatograph, a thermogravimetric analyzer, and other equipment, the changes of chemical composition and oxidation characteristics of particles were studied. The results show that as the methanol mixing ratio increases, the mass concentration of organic carbon (OC), bicyclic, and tricyclic polycyclic aromatic hydrocarbons (PAHs) in the particles increase, the mass concentration of elemental carbon (EC) and high molecular weight PAHs decreases, the concentration of nitrate ions first increases and then decreases, the activation energy decreases, and the oxidation activity increases. In general, the chemical composition of combustion particulates from methanol/biodiesel changes, and the oxidation activity is greatly improved. This research work can provide a reference for the coating design and regeneration strategy for optimizing diesel particulate filters (DPFs).

Source Apportionment of Elemental Carbon in Different Seasons in Hebei, China

Black carbon (BC), also termed elemental carbon (EC), is a strong light-absorbing substance. It can disturb the radiation balance between the earth and atmosphere resulting in changing regional and global climate conditions. This study conducted a thorough analysis of EC in Hebei during different seasons and provided comprehensive EC emission data in the Beijing–Tianjin–Hebei (BTH) region for future policy making connected with air pollution mitigation and control. The results showed that the concentration of EC during the sampling period varied from 0.01 to 18.4 μg/m3 with a mean value of 2.6 ± 2.8 μg/m3. The EC source apportionment exercise identified four regular emission sources for all seasons, including traffic-related emissions, coal combustion, biomass burning, and mineral dust. Annually, traffic-related emissions were the primary EC contributor with an annual average contribution of 38%, followed by biomass burning (30%) and coal combustion (25%). In addition, the EC mass concentration at Shijiazhuang was also influenced by diverse pollutants from upwind regions. This study shows that traffic emissions are a major contributor to EC mass concentration in Shangjiazhuang and highlights that regional joint control of air pollution is important to local air quality.

On the historic exposure levels of Elemental Carbon from vehicle diesel exhaust based on “diesel smoke” concentrations

Air pollution by diesel traffic became a concern in the UK in the 1950s. Exposure levels were assessed via probing the light absorption of filter samples, which was translated to a mass concentration of “diesel smoke” (DS), based on the results of a measurements in the exhaust of a test diesel engine. We convert these DS values to concentrations of Elemental Carbon (EC), the current proxy for diesel exhaust. In a recent study in the literature and an earlier own investigation a high similarity (R2 = 0.97) was found of the light absorption by aerosol collected in parallel on glass and quartz fibre filters and probed by smoke-stain reflectometers similar to those used historically. For samples on quartz fibre filters the relation between light absorption and EC was taken from recent studies. The shape of the absorption/EC curve is highly similar to the absorption/DS curve, with an equivalency factor of 1.6 ± 20% between DS and EC concentration (expressed according to the EUSAAR2-TOT method). Converted EC concentrations for workday average 24-hr and morning rush hour samples were around 75 and 150 μg m−3 at the kerbside of the busy London A1 ring-road in 1960. In 1961–1962 the average weekday daytime EC concentration at a traffic island in inner city Fleet Street was 200–250 μg m−3. Only 45 m into a side-street the concentration was an order of magnitude less. At the end of the 1990-ies EC concentrations at the nearby Marylebone Road were around 9 μg m−3, dropping to 3 μg m−3 in recent years. In addition, we found the correct factor to convert light absorption to EC mass concentration of samples obtained in the FH62 beta gauge monitors used in Germany in compliance measurements for the national “soot law” preceeding the EU PM10 regulation of 1997.

Seasonal variations of mass absorption efficiency of elemental carbon in PM2.5 in urban Guangzhou of South China

This study investigates seasonal variations of mass absorption efficiency of elemental carbon (MAEEC) and possible influencing factors in urban Guangzhou of South China. Mass concentrations of elemental carbon (EC) and organic carbon (OC) in PM2.5 and aerosol absorption coefficient (bap) at multi-wavelengths were simultaneously measured in four seasons of 2018–2019 at hourly resolution by a semi-continuous carbon analyzer and an aethalometer. Seasonal average mass concentrations of EC were in the range of 1.36–1.70 µgC/m3 with a lower value in summer than in the other seasons, while those of OC were in the range of 4.70–6.49 µgC/m3 with the lowest value in summer and the highest in autumn. Vehicle exhaust from local traffic was identified to be the predominant source of carbonaceous aerosols. The average aerosol absorption Ångström exponents (AAE) were lower than 1.2 in four seasons, indicating EC and bap were closely related with vehicle exhaust. Seasonal MAEEC at 550 nm was 11.0, 8.5, 10.4 and 11.3 m2/g in spring, summer, autumn, and winter, respectively. High MAEEC was related with the high mass ratio of non-carbonaceous aerosols to EC and high ambient relative humidity.

On the nonlinear relation between the Coefficient of Haze and Elemental Carbon mass concentration

ABSTRACT Coefficient of Haze (CoH) was the official proxy for the mass concentration of particulate matter in the US from ca. 1950 onwards. Originally, a linearity between CoH and sample load was claimed, but although shortly after the introduction of the method it was found that the relation between mass loading and the fraction of light 10 absorbed by the sample was identical to the nonlinear curve of the European “Black Smoke” (BS) method this correction was not officially adopted. We found that BS is a linear proxy for Elemental Carbon (EC) enabling an easy nonlinear conversion of CoH to EC concentration. Earlier it had been assumed that light-absorption by a sample is equal in the two methods, although CoH is obtained by light transmission while BS by light reflection. The “Filter Smoke Number” (FSN), used for diesel-soot emissions, is in essence the light-absorption by samples collected on the same filter type as in the CoH method (but probed in reflection). We noticed that the curve relating load and FSN is indistinguishable from the BS/EC curve. Ingram showed that light-absorption measured in reflection and transmission for this filter type is highly similar, so the standard BS/EC curve can be used to compare BS/EC and CoH. At low loadings the relation of EC concentration and CoH was quite similar to the equivalency factor of Black Carbon (BC) concentration and CoH. At CoH = 8, the historic limit of a severe smog day; however, the EC/BC-concentration alone was three times higher than that based on a (linear) equivalency factor. At CoH = 8, EC/BC mass concentrations alone reached the OSHA 8-hr workplace exposure limit of 150 µg m−3 for total carbon (the sum of organic carbon (OC) and EC). Implications: In this MS we show that the historic database of Coefficient of Haze (CoH) data can be converted to Elemental Carbon (EC) concentrations via several steps involving other historic and current measurement techniques (the European Black Smoke (BS) technique and techniques to measure Black Carbon (BC) and EC). The originally claimed linear relation between CoH and sample load is in reality a strongly nonlinear relation, so using the original linear relation leads to severe underestimations of historic EC concentrations especially on days with high concentrations of EC.

Comparison of co-located refractory black carbon (rBC) and elemental carbon (EC) mass concentration measurements during field campaigns at several European sites

Abstract. The mass concentration of black carbon (BC) particles in the atmosphere has traditionally been quantified with two methods: as elemental carbon (EC) concentrations measured by thermal–optical analysis and as equivalent black carbon (eBC) concentrations when BC mass is derived from particle light absorption coefficient measurements. Over the last decade, ambient measurements of refractory black carbon (rBC) mass concentrations based on laser-induced incandescence (LII) have become more common, mostly due to the development of the Single Particle Soot Photometer (SP2) instrument. In this work, EC and rBC mass concentration measurements from field campaigns across several background European sites (Palaiseau, Bologna, Cabauw and Melpitz) have been collated and examined to identify the similarities and differences between BC mass concentrations measured by the two techniques. All EC concentration measurements in PM2.5 were performed with the EUSAAR-2 thermal–optical protocol. All rBC concentration measurements were performed with SP2 instruments calibrated with the same calibration material as recommended in the literature. The observed values of median rBC-to-EC mass concentration ratios on the single-campaign level were 0.53, 0.65, 0.97, 1.20 and 1.29, respectively, and the geometric standard deviation (GSD) was 1.5 when considering all data points from all five campaigns. This shows that substantial systematic bias between these two quantities occurred during some campaigns, which also contributes to the large overall GSD. Despite considerable variability in BC properties and sources across the whole dataset, it was not possible to clearly assign reasons for discrepancies to one or the other method, both known to have their own specific limitations and uncertainties. However, differences in the particle size range covered by these two methods were identified as one likely reason for discrepancies. Overall, the observed correlation between rBC and EC mass reveals a linear relationship with a constant ratio, thus providing clear evidence that both methods essentially quantify the same property of atmospheric aerosols, whereas systematic differences in measured absolute values by up to a factor of 2 can occur. This finding for the level of agreement between two current state-of-the-art techniques has important implications for studies based on BC mass concentration measurements, for example for the interpretation of uncertainties in inferred BC mass absorption coefficient values, which are required for modeling the radiative forcing of BC. Homogeneity between BC mass determination techniques is also very important for moving towards a routine BC mass measurement for air quality regulations.

Influence of Meteorological Conditions and Fire Hotspots on PM0.1 in Northern Thailand during Strong Haze Episodes and Carbonaceous Aerosol Characterization

ABSTRACT Northern Thailand has long been severely affected by haze from biomass burning containing fine and ultrafine aerosols in the dry period. The carbonaceous PM0.1 comprising elemental carbon (EC) and organic carbon (OC) collected during the haze and non-haze periods in Chiang Mai, Thailand was investigated. The PM0.1 levels during the haze periods were about 3 times higher than the non-haze periods, a significant increase. PM0.1 concentration was strongly correlated with atmospheric relative humidity and the number of forest fire hotspots. Carbonaceous aerosol characteristics in PM0.1 were analyzed with the thermal/optical transmittance (TOT) method following the IMPROVE protocol. The concentrations of OC and EC, distribution of OC and EC and OC/EC ratios in PM0.1 were evaluated. Average OC and EC mass concentrations in PM0.1 were 6.8 ± 2.7 and 1.4 ± 0.5 µg m–3 during the haze periods, significantly higher than those during the non-haze periods; 1.9 ± 0.9 and 0.5 ± 0.2 µg m–3. The OC/EC ratio increased linearly with the number of hotspots. This indicated significant contribution from biomass burning to the PM0.1. This was strongly supported by the 48-hr backward trajectory simulation, that indicated both domestic and transboundary aerosol transports. Because both organic and elemental carbon are the light-absorbing carbonaceous aerosols, the increase during the haze periods contributed to regional air quality and climate. This study enhances the understanding of PM0.1 behavior in Chiang Mai, Thailand, during the haze periods in upper southeast Asia.

Smoke shade as a historic proxy for elemental carbon

The blackness of aerosol filter samples, meant as a proxy for particulate mass concentration, is the earliest parameter for which monitoring data exist. The smoke shade method (developed in the late 1910s) was the standardised approach to collect samples. The blackness was visually appraised by a comparison with a set of reference sheets covered with an increasing number of layers (shades) of a suspension of carbon black (ink). Samples were assigned a shade number (SN) according to the number of shades of ink on the reference sheet with a corresponding blackness. Automated hourly sampling started in 1921. After World War II, the blackness was measured with a reflectometer and light absorption was translated to the parameter British Smoke (BrS). One unit of SN was equivalent to a specific loading of BrS of 8 μg cm−2. BrS in turn is a proxy for elemental carbon (EC) as we showed in an earlier publication, where we found that a value of BrS of 8 μg cm−2 corresponded to an EC load of 1.4 μg cm−2. SNs can thereby be translated to historic EC loadings/concentrations. In an evaluation of SN-data, we noticed that average pre-war values were mostly at the lower detection limit (one SN) and overestimated because reference sheets faded over time. Data for smog periods with their elevated SNs, however, are quite reliable and can be used for exposure estimates. After World War II, daily sampling resulted in higher filter loadings and reliable average values. Wintertime concentrations corresponding to up to 100 μg m−3 EC were reached. On the other hand, the increased loadings due to the long sampling times resulted in a decrease of the upper limit of detection to an extent that it was exceeded at most of the measuring stations during the “Great Smog” of London in 1952. In this study, we analysed SN data from this episode in depth. At one measuring site, precautions were taken to minimise the loading by using a large filter, but even then the maximum SN was at the upper limit of detection. From a one-to-one relation of BrS and gravimetric mass, established during later smog periods, we deduced that the maximum 2-day mass concentration of EC must have been around 1000 μg m−3. This value is twenty times the new EU-limit for workplace EC exposure (EU 2019) and the 24-h ambient PM10 mass concentration.

Exploratory analysis of carbonaceous PM2.5 species in urban environments: Relationship with meteorological variables and satellite data

The carbonaceous chemical composition and mass concentration of particles with an aerodynamic diameter less than 2.5 μm (PM2.5), were analyzed, as well as their relationship with satellite data and meteorological variables. PM2.5 ground samples were collected at nine sampling sites with different land use in the metropolitan area of Córdoba city, during autumn and winter in 2018, and concentrations of organic carbon (OC) and elemental carbon (EC) were measured. The aerosol optical depth (AOD) was retrieved from the MODIS sensor, Aqua and Terra satellites. The AOD was validated using ground-based sun photometer data. Furthermore, the PM2.5 mass concentration and composition were simulated using multiple linear regression models, with the measured AOD and meteorological parameters as input variables. The data showed that PM2.5 mass concentrations varied in space throughout the city, indeed at four sampling sites, they exceeded the World Health Organization (WHO) daily guidelines. The OC and EC mass concentrations were moderate and low, respectively, in comparison with other cities in the world. PM2.5 concentrations were negatively associated with average planetary boundary layer (PBLav), dew point (DP) and AOD from Aqua satellite (AODa). The columnar average AODav did not correlate significantly with the ground-based PM2.5 measurements, however AODa was retained in a model to explain PM2.5 having a negative effect on particles. An effective carbon ratio (ECR) was calculated to estimate the radiative forcing of PM2.5 in a local scale. The results suggested an overall local radiative heating effect due to PM2.5.

Size and chemical characteristics of particles emitted from typical rural biomass cookstoves in North China

The emission characteristics of biomass combustion in rural household stoves were measured in northern China. The Electrical Low-Pressure Impactor plus (ELPI+) was used to collect the emitted particles in the size range of 0.006–9.890 μm. The particle number concentration (PNC), particle mass concentration (PMC), and size distribution characteristics of organic carbon (OC), elemental carbon (EC), and water-soluble ions were analyzed. The experimental results showed that the PNC peaked at 0.006–0.030 μm, and the PMC peaked at 0.257–0.603 μm. The mass concentration of OC and EC exhibited a “bell-shaped” size distribution in the 0–10 μm range. The OC content of particles reached its peak at 0.006–0.016 μm and ranged from 25% to 38%. The mass concentration and percentage of K+ and Cl− showed “bell-shaped” size distribution characteristics and the contents of K+ and Cl− in each particle size group were significantly correlated. The chemical source profiles of PM0.1, PM1, PM2.5, and PM10 were constructed, whose main components were OC, EC, K+, and Cl−. PM2.5 profile included 8.39–20.27% OC, 1.94–20.96% EC, 0.25–13.36% K+, and 0.36–16.97% Cl−.

Characterization and Size Distribution of Carbonaceous Aerosols at Mountain Dinghu

To understand the characterization and sources of carbonaceous aerosols at Mountain Dinghu, organic carbon (OC) and elemental carbon (EC) in size-resolved aerosol samples were measured at a regional background site in South China using a DRI Model 2001A analyzer. The average mass concentrations of organic carbon (OC) are (5.6±2.0) μg ·m-3 in PM1.1, (7.3±2.4) μg ·m-3 in PM2.1, and (12.8±4.0) μg ·m-3 in PM9.0; the average mass concentrations of elemental carbon (EC) are (2.3±1.4) μg ·m-3in PM1.1, (2.7±1.6) μg ·m-3 in PM2.1, and (3.4±1.7) μg ·m-3 in PM9.0. OC concentrations in PM1.1 and PM2.1 account for 43.8% and 57.0% of OC in PM9.0, and EC concentrations in PM1.1 and PM2.1 account for 67.6% and 79.4%, respectively. OC and EC are enriched with fine particles. In PM1.1 and PM2.1, the highest concentrations of OC and EC are measured in autumn, and the lowest concentration of OC is measured in winter and EC in summer. In PM9.0, the highest OC concentration is measured in summer. Carbonaceous aerosols are mainly composed of OC2, EC1, OC3, and OC4. In summer, the concentration of OC3 is higher than that of EC1, suggesting that biogenic sources are dominant during summer. The concentration of EC1 in winter is the highest, indicating that the impacts of motor vehicle emissions are prominent in the local area during winter. OC and EC both show bimodal distributions in four seasons, with peaks in the size ranges of 0.43-0.65 μm for fine particles and 3.3-5.8 μm for coarse particles. In PM1.1 and PM2.1, the sources of OC are mainly primary emissions. In PM2.1, the highest concentration of SOC is measured in spring at (3.0±1.4) μg ·m-3 and the lowest in winter at (1.3±1.4) μg ·m-3, indicating that the secondary aerosol formation is significant in spring. At the Mountain Dinghu background site, OC is mainly from coal combustion and motor vehicle emissions for fine particles and from biogenic sources for coarse particles. EC is mainly from coal combustion, motor vehicle emissions, and dust.

High mass absorption efficiency of carbonaceous aerosols during the biomass burning season in Chiang Mai of northern Thailand

Abstract Southeast Asia is one of the major regions of biomass burning in the world. To investigate the light absorption properties of carbonaceous aerosols produced from biomass burning, mass concentrations of PM2.5 and its major chemical compositions were obtained by filter sampling, and aerosol absorption coefficient (bap) at 370 nm (bap-370nm) and at 880 nm (bap-880nm) were synchronously determined for the sampled filters using a transmissometer in urban Chiang Mai of Northern Thailand during the dry season in 2019. On campaign average, the reconstructed PM2.5 mass from the measured chemical components accounted for 99% of the measured PM2.5 mass, in which organic matters (OM) accounted for 64 ± 10%. Hardwood burning was identified as the dominant source of carbonaceous aerosols. The measured aerosol absorption Angstrom exponent (AAE) at 370–880 nm (AAE370–880nm) was 1.71 ± 0.24. Mass absorption efficiency (MAE) of elemental carbon (EC) and organic carbon (OC) was estimated using a multiple linear regression model between bap and mass concentrations of EC and OC, resulting in campaign-average values of 8.11 m2 g−1 and 0.24 m2 g−1 at 880 nm and 21.06 m2 g−1 and 2.57 m2 g−1 at 370 nm, respectively, which were evidently larger than those in other cities worldwide. The contributions of EC to bap in 370–880 nm spectrum region ranged from 49 ± 5% to 79 ± 3%, and those of OC ranged from 51 ± 5% to 21 ± 3%. Results from this study suggested a potentially significant impact of carbonaceous aerosols on direct radiative forcings in the dry season over Southeast Asia and downwind regions.

Effect of sodium chloride on the evolution of size, mixing state, and light absorption of soot particles from a smoking laminar diffusion flame

In this study, the effect of sodium chloride (NaCl) on the evolution of size, mixing state, and optical properties of particle emissions was investigated. A smoking laminar diffusion flame of methane with flame length of ~100 mm was used, with and without NaCl particles introduced into the fuel stream. Extractive probe sampling with high dilution was used to sample particles and characterize their size and mixing state. Particle size distribution results showed that for the methane-only flame, the soot particles underwent typical processes of formation and coagulation in the flame, partial oxidation near the flame tip, and further coagulation in the post-flame region. In the case of the methane–NaCl flame, the coagulation rate between soot particles decreased in the agglomeration region of the flame, resulting in smaller soot particles with higher number concentration. Near the open tip of the flame, the NaCl inhibited soot oxidation, leading to larger particles compared to the methane-only flame due to continued coagulation and reduced oxidation of soot particles. In the post-flame region, where the temperature was sufficiently low, NaCl particles nucleated from its vapour phase, which was a distinct mode from that of soot in the particle size distributions. Electron microscopy images showed that these nucleated NaCl particles were mostly externally mixed and occasionally internally mixed with soot particles. Thermal-optical analysis of emissions sampled from post-flame region showed that the mass concentration of elemental carbon increased by a factor of ~3 when NaCl was added to the flame. However, addition of NaCl did not affect the mass-specific absorption coefficient of particle emissions, which was within previously reported values in the literature.

Contribution of various types and categories of diesel-powered vehicles to aerosols in an underground mine

A study was conducted in an underground mine with the objective to assess relative contributions of different types and categories of diesel-powered vehicles to submicron aerosol concentrations and to assess the effectiveness of selected diesel particulate matter control strategies and technologies. The net contributions of each of six heavy-duty (HD) vehicles, five light-duty (LD) vehicles, and the effects of disposable filter elements (DFEs), a sintered metal filter (SMF) system, and repowering were assessed using isolated zone methodology. On average, the HD vehicles powered by engines that were not retrofitted with filtration systems contributed approximately three times more to the number of aerosols and six times more to elemental carbon (EC) mass concentrations than LD vehicles powered by engines that were not retrofitted with filtration systems. Replacing an Environmental Protection Agency (EPA) pre-Tier engine in the non-permissible HD vehicle with an EPA Tier 3 engine resulted in 63% lower EC concentrations and 41% lower aerosol number concentrations. The evaluated filtration system with DFEs reduced the contribution of diesel-powered vehicles to number concentrations of aerosols by 77 to 92% and the average EC concentrations by 95%. The SMF reduced the contribution of diesel-powered vehicles to number concentrations of aerosols and EC concentrations by 93 and 95%, respectively. When compared with older units, one of the newer model personnel carriers contributed noticeably less to EC mass concentrations but almost equally to the number concentrations of diesel aerosols in the mine air. The second newer type of alternative personnel carrier vehicle contributed more to number and EC mass concentrations than the old-style personnel carrier. The LD vehicle powered by an EPA Tier 4f engine equipped with a DPF system contributed least of all tested vehicles to aerosol number and EC mass concentrations. This information is critical to the efforts of the underground mining industry to reduce exposures of workers to diesel aerosols.

State of knowledge on the occupational exposure to carbon nanotubes.

Carbon nanotubes (CNT) trigger fascination as well as anxiety, given their unique physical and chemical properties, and continuing concerns around their possible health effects. CNT exposure assessment is an integral component of occupational and environmental epidemiology, risk assessment, and management. We conducted a systematic review to analyze the quality of CNT occupational exposure assessments in field studies and to assess the relevance of available quantitative data from occupational hygiene and epidemiological perspectives. PubMed and Scopus databases were searched for the period 2000-2018. To grade the quality of each study, we used a standardized grid of seven criteria. The first criterion addressed 12 items deemed most relevant CNT physical-chemical properties with respect to their in vitro and in vivo toxicity. We included 27 studies from 11 countries in the review and graded them high (n=2), moderate (n=15) and low quality (n=10). Half of the studies measured elemental carbon mass concentration (EC) using different methods and aerosol fractions. In 85% of studies, the observed values exceed the US National Institute for Occupational Safety and Health Recommended Exposure Limit. The quantification of CNT agglomerates and/or CNT contained fibers becomes increasingly common although lacking methodological standardization. Work activities with the greatest mean CNT mass concentrations were non-enclosed and included sieving, harvesting, packaging, reactor cleaning, extrusion and pelletizing. Some of the large studies defined standardized job titles according to exposure estimates at corresponding workstations and classified them by decreasing CNT exposure level: technicians>engineers>chemists. The already initiated harmonization of CNT exposure assessment and result reporting need to continue to favor not only studies in the field, but also to identify companies and workers using CNTs to characterize their exposures as well as monitor their health. This will enable an objective and realistic evaluation of risks associated with CNT applications and an appropriate risk management.

Retrofitting and re-powering as a control strategies for curtailment of exposure of underground miners to diesel aerosols.

A study was conducted to examine the potential of diesel emissions control strategies based on retrofitting existing power packages with exhaust aftertreatment devices and repowering with advanced power packages. The retrofit systems, a diesel oxidation catalyst (DOC) and diesel particulate filter (DPF), were evaluated individually using a US EPA tier 2 (ter 2) engine operated under four steady-state conditions and one transient cycle. The DOC effectively curtailed emissions of CO, and to some extent organic carbon (OC), elemental carbon (EC), and aerosol number concentration. The DPF system offered substantially higher reductions in OC and EC mass and aerosol number concentrations. Both, the DOC and DPF achieved reductions in the aforementioned emissions without adversely affecting emissions of NO2 and nano-sized aerosols. The strategy of repowering with an advanced system was examined using a US EPA tier 4 final (tier 4f) engine equipped with a cooled exhaust gas recirculation system and diesel exhaust fluid-based selective catalytic reduction system, but not with a DPF system. The tier 4f engine contributed substantially less than the tier 2 engine to the EC and OC mass, aerosol number, and CO, NO, and NO2 concentrations. The tier 4f engine was very effective in reducing aerosol mass, NO, and NO2 concentrations, but it was not equally effective in reducing aerosol number concentrations. The implementation of viable exhaust after treatment systems and advanced diesel power packages could be instrumental to the underground mining industry to secure a clean, economical, and dependable source of power for mobile equipment.

Molecular Composition and Source Apportionment of Fine Organic Aerosols in Autumn in Changchun

Organic aerosols have attracted increasing attention recently due to their significant contribution to fine particles (PM2.5) and their complex components and sources. In this study, a total of 40 PM2.5 samples were collected simultaneously with high-volume samplers in Changchun from 16th Oct to 29th Nov 2016. Organic carbon (OC), elemental carbon (EC), non-polar organic compounds including n-alkanes, polycyclic aromatic hydrocarbons (PAHs), and hopanes, and levoglucosan in atmospheric fine particles were analyzed. The main sources of organic aerosols were identified by molecular markers, diagnostic ratios, and a principal component analysis-multiple liner regression (PCA-MLR) model. The results showed that the average mass concentration of PM2.5 was (79.0±55.7) μg·m-3, and the averaged OC and EC mass concentrations were (20.7±15.6) μg·m-3 and (2.2±1.1) μg·m-3, which accounted for 26.2% and 2.8% of PM2.5, respectively. The total average concentration of the tested non-polar organic compounds was (186.3±104.5) ng·m-3 and, in descending order, this was composed of n-alkane (101.3±67.0) ng·m-3, polycyclic aromatic hydrocarbons (81.4±46.0) ng·m-3, hopanes (3.8±1.9) ng·m-3. The PCA-MLR model results showed that the relative contributions of the main sources of organic aerosols were coal combustion (47.0%), biomass burning (42.6%), and traffic emission (10.4%).

Impact of air pollution control measures and regional transport on carbonaceous aerosols in fine particulate matter in urban Beijing, China: insights gained from long-term measurement

Abstract. As major chemical components of airborne fine particulate matter (PM2.5), organic carbon (OC) and elemental carbon (EC) have vital impacts on air quality, climate change, and human health. Because OC and EC are closely associated with fuel combustion, it is helpful for the scientific community and policymakers assessing the efficacy of air pollution control measures to study the impact of control measures and regional transport on OC and EC levels. In this study, hourly mass concentrations of OC and EC associated with PM2.5 were semi-continuously measured from March 2013 to February 2018. The results showed that annual mean OC and EC concentrations declined from 14.0 to 7.7 µg m−3 and from 4.0 to 2.6 µg m−3, respectively, from March 2013 to February 2018. In combination with the data of OC and EC in previous studies, an obvious decreasing trend in OC and EC concentrations was found, which was caused by clean energy policies and effective air pollution control measures. However, no obvious change in the ratios of OC and EC to the PM2.5 mass (on average, 0.164 and 0.049, respectively) was recorded, suggesting that inorganic ions still contributed a lot to PM2.5. Based on the seasonal variations in OC and EC, it appeared that higher OC and EC concentrations were still observed in the winter months, with the exception of winter of 2017–2018. Traffic policies executed in Beijing resulted in nighttime peaks of OC and EC, caused by heavy-duty vehicles and heavy-duty diesel vehicles being permitted to operate from 00:00 to 06:00 (China standard time, UTC+8, for all times throughout the paper). In addition, the fact that there was no traffic restriction in weekends led to higher concentrations on weekends compared to weekdays. Significant correlations between OC and EC were observed throughout the study period, suggesting that OC and EC originated from common emission sources, such as exhaust of vehicles and fuel combustion. OC and EC levels increased with enhanced SO2, CO, and NOx concentrations while the O3 and OC levels were enhanced simultaneously when O3 concentrations were higher than 50 µg m−3. Non-parametric wind regression analysis was performed to examine the sources of OC and EC in the Beijing area. It was found that there were distinct hot spots in the northeast wind sector at wind speeds of approximately 0–6 km h−1, as well as diffuse signals in the southwestern wind sectors. Source areas further away from Beijing were assessed by potential source contribution function (PSCF) analysis. A high-potential source area was precisely pinpointed, which was located in the northwestern and southern areas of Beijing in 2017 instead of solely in the southern areas of Beijing in 2013. This work shows that improvement of the air quality in Beijing benefits from strict control measures; however, joint prevention and control of regional air pollution in the regions is needed for further improving the air quality. The results provide a reference for controlling air pollution caused by rapid economic development in developing countries.

Chemical composition and radiative properties of nascent particulate matter emitted by an aircraft turbofan burning conventional and alternative fuels

Abstract. Aircraft engines are a unique source of carbonaceous aerosols in the upper troposphere. There, these particles can more efficiently interact with solar radiation than at ground. Due to the lack of measurement data, the radiative forcing from aircraft exhaust aerosol remains uncertain. To better estimate the global radiative effects of aircraft exhaust aerosol, its optical properties need to be comprehensively characterized. In this work we present the link between the chemical composition and the optical properties of the particulate matter (PM) measured at the engine exit plane of a CFM56-7B turbofan. The measurements covered a wide range of power settings (thrust), ranging from ground idle to take-off, using four different fuel blends of conventional Jet A-1 and hydro-processed ester and fatty acids (HEFA) biofuel. At the two measurement wavelengths (532 and 870 nm) and for all tested fuels, the absorption and scattering coefficients increased with thrust, as did the PM mass. The analysis of elemental carbon (EC) and organic carbon (OC) revealed a significant mass fraction of OC (up to 90 %) at low thrust levels, while EC mass dominated at medium and high thrust. The use of HEFA blends induced a significant decrease in the PM mass and the optical coefficients at all thrust levels. The HEFA effect was highest at low thrust levels, where the EC mass was reduced by up to 50 %–60 %. The variability in the chemical composition of the particles was the main reason for the strong thrust dependency of the single scattering albedo (SSA), which followed the same trend as the fraction of OC to total carbon (TC). Mass absorption coefficients (MACs) were determined from the correlations between aerosol light absorption and EC mass concentration. The obtained MAC values (MAC532=7.5±0.3 m2 g−1 and MAC870=5.2±0.9 m2 g−1) are in excellent agreement with previous literature values of absorption cross section for freshly generated soot. While the MAC values were found to be independent of the thrust level and fuel type, the mass scattering coefficients (MSCs) significantly varied with thrust. For cruise conditions we obtained MSC532=4.5±0.4 m2 g−1 and MSC870=0.54±0.04 m2 g−1, which fall within the higher end of MSCs measured for fresh biomass smoke. However, the latter comparison is limited by the strong dependency of MSC on the particles' size, morphology and chemical composition. The use of the HEFA fuel blends significantly decreased PM emissions, but no changes were observed in terms of EC∕OC composition and radiative properties.