Chemical Characteristics of Fine Particles (PM1) from Xi'an,China

Daily mass concentrations of water-soluble inorganic (WS-i) ions, organic carbon (OC), and elemental carbon (EC) were determined for fine particulate matter (PM₁, particles < 1.0 μm in diameter) collected at Xi'an, China. The annual mean PM₁ mass concentration was 127.3 ± 62.1 μg m^–3: WS-i ions accounted for ～38% of the PM₁ mass; carbonaceous aerosol was ～30%; and an unidentified fraction, probably mostly mineral dust, was ～32%. WS-i ions and carbonaceous aerosol were the dominant species in winter and autumn, whereas the unidentified fraction had stronger influences in spring and summer. Ion balance calculations indicate that PM₁ was more acidic than PM_2.5 from the same site. PM₁ mass, sulfate and nitrate concentrations followed the order winter > spring > autumn > summer, but OC and EC levels were higher in autumn than spring. Annual mean OC and EC concentrations were 21.0 ± 12.0 μg m^?3 and 5.1 ± 2.7 μg m^–3 with high OC/EC ratios, presumably reflecting emissions from coal combustion and biomass burning. Secondary organic carbon, estimated from the minimum OC/EC ratios, comprised 28.9% of the OC. Positive matrix factorization (PMF) analysis indicates that secondary aerosol and combustion emissions were the major sources for PM₁.     

An Inter-Comparison of Two Black Carbon Aerosol Instruments and a Semi-Continuous Elemental Carbon Instrument in the Urban Environment

Aerosol absorption coefficients were obtained using two versions of the Magee Scientific Aethalometer and a Particle Soot Absorption Photometer (PSAP) in Riverside, California during July and August of 2005. These measurements were subsequently compared to each other and to hourly elemental carbon (EC) mass concentrations as determined by a Sunset Labs semi-continuous OCEC analyzer. Measurements from all four instruments were shown to be highly correlated (R ² = 0.83 to 0.92). Differences between absorption values measured by the PSAP and the Aethalometer were found to be dominated by differences in the filter media used by the respective instruments. Comparison of optical and thermal measurements revealed that the specific attenuation cross section (σ _ATN ) of light absorbing carbon (LAC) varied as a function of the time of the day, most notably during weekdays. Minimum σ _ATN values were observed during morning rush hour when EC concentrations were at their greatest and maxima were seen in the late afternoon. These variations correlated with changes in the OC/EC ratio and the Angstrom exponent for absorption, which is consistent with changes in the mixing state of elemental carbon associated with secondary aerosol condensation on primary EC particles.     

A Temperature Calibration Procedure for the Sunset Laboratory Carbon Aerosol Analysis Lab Instrument

The Sunset Laboratory Carbon Aerosol Analysis Lab Instrument is widely used for thermal-optical analysis (TOA) of ambient particulate matter samples to measure total carbon (TC), organic carbon (OC), and elemental carbon (EC), and often thermal sub-fractions of OC and EC. TOA operating protocols include a series of plateau temperatures at which the thermal sub-fractions evolve. The temperatures have conventionally been measured by a sensor located in the sample oven but away from the filter sample. However, the TOA protocol used by the Interagency Monitoring of Protected Visual Environments (IMPROVE) network and recently adopted by the U.S. Environmental Protection Agency (EPA) Speciation Trends Network (STN) and Chemical Speciation Network (CSN) specify temperatures to be achieved at the filter. Our goal was to develop a simple calibration method to obtain the target filter temperatures in a Sunset Instrument. This method showed good agreement with the IMPROVE/STN/CSN method and has the advantages of not damaging oven components and of providing a direct comparison of sample oven sensor and filter temperatures at the TOA protocol-specified temperatures. Calibrations performed on four Sunset Instruments yielded different sensor/filter temperature relationships. Ambient PM _2.5 samples analyzed using IMPROVE_A temperatures at the oven sensor compared to IMPROVE_A temperatures at the filter yielded statistically insignificant differences for TC, OC, and EC but statistically significant differences for the carbon sub-fraction concentrations. Temperature calibrations should be performed on each Sunset Instrument to ensure comparability in the carbon sub-fractions being reported, and a simple method has been provided for performing these calibrations.     

Investigating a Liquid-Based Method for Online Organic Carbon Detection in Atmospheric Particles

A Particle-Into-Liquid Sampler (PILS) was modified and coupled with a Total Organic Carbon (TOC) Analyzer (Sievers 800T, GE Water Systems, Boulder, CO), in an attempt to measure particulate organic carbon (OC) online. The PILS droplet collection system was changed from an inertial impactor to a miniature cyclone to increase the efficiency of transferring insoluble carbonaceous aerosol to the liquid sample stream. The performance of the modified PILS was investigated with a variety of calibration aerosols through comparison with the Sunset Labs ECOC technique (NIOSH method 5040). Linear regression slopes of water-soluble organic compounds compared well with Sunset Labs measurement, agreeing to within 5%. However, a size dependence was observed when comparing insoluble carbonaceous aerosol (polystyrene latex spheres, PSL). The new method did not effectively measure insoluble particles with aerodynamic diameters greater than ～ 110 nm due to inefficient analysis by the TOC. The OC measurement method was also compared with online Sunset Labs organic carbon (OC) measurements in two urban locations: Atlanta, GA, and Riverside, CA. Linear regression slopes between the PILS technique and Sunset Labs were near unity (101% to 93% ± 2 and 5%, respectively), and not statistically different from unity considering the measurement uncertainty of each method. However there was a significant (0.6 to 1.7 μ gC m ^{? 3} ) non-zero intercept, with the Sunset Labs instrument measuring higher concentrations, possible due to the inability of the PILS to measure large, insoluble particles or positive artifacts with the non-blank corrected Sunset Labs filter-based collection method.     

PM1.0 and PM2.5 Characteristics in the Roadside Environment of Hong Kong

Daily mass concentrations of PM _1.0 (particles less than 1.0 μm in diameter), PM _2.5 (particles less than 2.5 μm in diameter), organic carbon (OC), and elemental carbon (EC) were measured from January through May 2004 at a heavily trafficked sampling site in Hong Kong (PU). The average concentrations for PM _1.0 and PM _2.5 were 35.9 ± 12.4 μ g cm ^{? 3} and 52.3 ± 18.3 μ g cm ^{? 3} . Carbonaceous aerosols were the dominant species in fine particles, accounting for ～ 45.7% of PM _1.0 and ～ 44.4% of PM _2.5 . During the study period, seven fine-particle episodes occurred, due to the influence of long-range transport of air masses from mainland China. PM _1.0 and PM _2.5 responded in similar ways; i.e., with elevated mass and OC concentrations in those episode days. During the sampling period, PM _1.0 OC and EC generally behaved similarly to the carbonaceous aerosols in PM _2.5 , regardless of seasonal variations and influence by regional pollutions. The low and relatively constant OC/EC ratios in PM _1.0 and PM _2.5 indicated that vehicular emissions were major sources of carbonaceous aerosols. PM _1.0 and PM _2.5 had the same dominant sources of vehicular emissions in winter, while in spring PM _2.5 was more influenced by PM _{1 ? 2.5} (particles 1–2.5 μ m in diameter) that did not form from vehicle exhausts. Therefore, PM _1.0 was a better indicator for vehicular emissions at the Roadside Station.     

Thermal/optical reflectance equivalent organic and elemental carbon determined from federal reference and equivalent method fine particulate matter samples using Fourier transform infrared spectrometry

A fine particulate matter (PM_2.5) monitoring network of filter-based federal reference methods and federal equivalent methods (FRM/FEMs) is used to assess local ambient air quality by comparison to National Ambient Air Quality Standards (NAAQS) at about 750 sites across the continental United States. Currently, FRM samplers utilize polytetrafluoroethylene (PTFE) filters to gravimetrically determine PM_2.5 mass concentrations. At most of these sites, sample composition is unavailable. In this study, we present the proof-of-principle estimation of the carbonaceous fraction of fine aerosols on FRM filters using a nondestructive Fourier transform infrared (FT-IR) method. Previously, a quantitative FT-IR method accurately determined thermal/optical reflectance equivalent organic and elemental carbon (a.k.a., FT-IR organic carbon [OC] and elemental carbon [EC]) on filters collected from the chemical speciation network (CSN). Given the similar configuration of FRM and CSN aerosol samplers, OC and EC were directly determined on FRM filters on a mass-per-filter-area basis using CSN calibrations developed from nine sites during 2013 that have collocated CSN and FRM samplers. FRM OC and EC predictions were found to be comparable to those of the CSN on most figures of merit (e.g., R²) when the type of PTFE filter used for aerosol collection was the same in both networks. Although prediction accuracy remained unaffected, FT-IR OC and EC determined on filters produced by a different manufacturer show marginally increased prediction errors suggesting that PTFE filter type influences extending CSN calibrations to FRM samples. Overall, these findings suggest that quantifying FT-IR OC and EC on FRM samples appears feasible.

© 2018 American Association for Aerosol Research     

Fine particles sampled at an urban background site and an industrialized coastal site in Northern France—Part 2: Comparison of offline and online analyses for carbonaceous aerosols

Particulate matter was sampled in Northern France during two summer and winter periods at both an urban background site (Douai, DO) and an industrialized coastal site (Grande-Synthe, GS). Ambient levels of particulate carbonaceous species and Polycyclic Aromatic Hydrocarbons (PAH) were measured by real-time measurements and via collection and analysis of offline filters (F). The comparison between online organic matter (OM) measured by an Aerosol Mass Spectrometer (AMS) and organic carbon (OC) determined by an offline thermal-optical method showed good linear trends in wintertime GS (r² = 0.82 while only 0.50 in summer), and DO (r² = 0.86 in summer and 0.92 in winter). However, significant differences were observed between analytical methods and sites with OC_AMS/OC_F ratios decreasing from 0.80 in DO during winter to ≈0.20 for GS in summer, suggesting that a large part of OM could be in the PM₁–PM_2.5 fraction. The simultaneous measurements of Black Carbon (BC) and Elemental Carbon (EC) concentrations in PM_2.5 were also well correlated at both sites with r² = 0.61–0.97 and slopes between 0.6 and 0.8. PAHs were analyzed in PM_2.5 and also measured online by AMS in PM₁. Their wintertime concentrations were highly correlated in DO (r² = 0.98) and to a lesser degree in GS (r² = 0.67). r² values determined for comparison between online and offline parameters (OC and PAHs) in GS were lower than in DO, probably due to a more complex aerosol composition and a higher variability of the physical and chemical properties resulting from the coastal situation and diversity of emission sources in the vicinity of GS.

Copyright © 2018 American Association for Aerosol Research     

Major Source Categories for PM2.5 in Pittsburgh using PMF and UNMIX

An objective of the Pittsburgh Air Quality Study was to determine the major sources of PM_2.5 in the Pittsburgh region. Daily 24-hour averaged filter-based data were collected for 13 months, starting in July 2001, including sulfate and nitrate data from IC analysis, trace element data from ICP-MS analysis, and organic and elemental carbon from the thermal optical transmittance (TOT) method and the NIOSH thermal evolution protocol. These data were used in two source-receptor models, Unmix and PMF. Unmix, which is limited to a maximum number of seven factors, resolved six source factors, including crustal material, a regional transport factor, secondary nitrate, an iron, zinc and manganese factor, specialty steel production and processing, and cadmium. PMF, which has no limit to the number of factors, apportioned the PM_2.5 mass into ten factors, including crustal material, secondary sulfate, primary OC and EC, secondary nitrate, an iron, zinc and manganese factor, specialty steel production and processing, cadmium, selenium, lead, and a gallium-rich factor. The Unmix and PMF common factors agree reasonably well, both in composition and contributions to PM_2.5. To further identify and apportion the sources of PM_2.5, specific OC compounds that are known markers of some sources were added to the PMF analysis. The results were similar to the original solution, except that the primary OC and EC factor split into two factors. One factor was associated with vehicles as identified by the hopanes, PAH's, and other OC compounds. The other factor had strong correlations with the OC and EC ambient data as well as wood smoke markers such as levoglucosan, syringols, and resin acids.     

Mass Absorption Cross-Section of Ambient Black Carbon Aerosol in Relation to Chemical Age

Three differing techniques were used to measure ambient black carbon (BC) aerosols in downtown Toronto through 20 December 2006 to 23 January 2007. These techniques were thermal analysis, as performed by a Sunset Labs OCEC Analyzer (OCEC); light attenuation, as performed by an Aethalometer (AE); and photoacoustic analysis, as performed by a Photoacoustic Instrument (PA). These measurements of ambient PM _2.5 were used to investigate the effects of coating thickness on BC Mass Absorption Cross-section (MAC). MAC values were determined by comparing 880 nm and 370 nm AE measurements and PA measurements of b _abs (absorption coefficient, Mm^–1) to the OCEC measurements. Based on mass size distributions and supporting criteria, the PM _2.5 was classified as fresh, semi-aged, or aged. The average MAC values in these categories, based on the PA measurements, were 9.3 ± 1.8, 9.9 ± 2.0, and 9.3 ± 2.2 m ² /g (mean ± standard deviation), respectively, suggesting that any difference in coating thickness as a result of aging, on the time scale observed, did not produce a difference in MAC. In a second type of experiment, a thermodenuder was installed upstream of the AE, PA, and OCEC and samples were heated to 340°C in order to evaporate volatile and semi-volatile components within the coating. Based on the PA measurements, the average MAC values of these heated samples, for the fresh, semi-aged, and aged categories were 7.7 ± 2.2, 6.9 ± 2.2, and 9.1 ± 2.0 m ² /g, respectively. Similar differences in MAC were also observed by the AE. The decrease in MAC in the fresh and semi-aged samples was interpreted in terms of the degree of coating of the PM _2.5 . Results agreed well with predictions made by absorption amplification theory and had ramifications for calibration of filter-base attenuation and photoacoustic instruments.     

Chemical Mass Closure and Chemical Characteristics of Ambient Ultrafine Particles and other PM Fractions

Ambient ultrafine particles (UPs or PM _0.1 ), PM _2.5 and PM ₁₀ were investigated at the roadside of Syuefu road in Hsinchu city and in the Syueshan highway tunnel in Taipei, Taiwan. A SMPS (TSI Model 3936), three Dichotomous samplers (Andersen Model SA-241), and three MOUDIs (MSP Model 110) were collocated to determine the PM number and mass concentrations simultaneously. The filter samples were further analyzed for organic carbon (OC), element carbon (EC), water-soluble ions, and trace elements. The OC artifact was studied and quantified using the quartz behind quartz (QBQ) method for all PM fractions. Taking into account the OC artifact, chemical mass closure (ratio of the reconstructed chemical mass to the gravimetrical mass) of PM _0.1 , PM _2.5 , and PM ₁₀ was then calculated and found to be good. The chemical analysis results of UPs at both sites showed that UPs in the present tunnel was mostly contributed from the vehicle emissions while UPs at the roadside was mainly influenced by urban sources.     

Development and Laboratory Performance Evaluation of a Personal Multipollutant Sampler for Simultaneous Measurements of Particulate and Gaseous Pollutants

A personal multipollutant sampler has been developed. This sampler can be used for measuring exposures to particulate matter and criteria gases. The system uses asingle personalsampling pump that operates at a flow rate of 5.2 l/min. The basic unit consists of two impaction-based samplers for PM_2.5 and PM₁₀ attached to a single elutriator. Two mini PM_2.5 samplers are also attached to the elutriator for organic carbon (OC), elemental carbon (EC), sulfate, and nitrate measurements. For the collection of nitrate and sulfate, the minisampler includes a miniaturized honeycomb glass denuder that is placed upstream of the filter to remove nitric acid and sulfur dioxide and to minimize artifacts. Two passive samplers can also be attached to the elutriator for measurements of gaseous copollutants such as O₃, SO₂, and NO₂. The performance of the multipollutant sampler was examined through a series of laboratory chamber tests. The results showed a good agreement between the multipollutant sampler and the reference methods. The overall sampler performance demonstrates its suitability for personal exposure assessment studies.     

Sensitivity of Diesel Particulate Material Emissions and Composition to Blends of Petroleum Diesel and Biodiesel Fuel

A number of investigations have examined the impact of the use of biodiesel on the emissions of carbon dioxide and regulated emissions, but limited information exists on the chemical composition of particulate matter from diesel engines burning biodiesel blends. This study examines the composition of diesel particulate matter (DPM) emissions from a commercial agriculture tractor burning a range of biodiesel blends operating under a load that is controlled by a power take off (PTO) dynamometer. Ultra-low sulfur diesel (ULSD) fuel was blended with soybean and beef tallow based biodiesel to examine fuels containing 0% (B0), 25% (B25), 50% (B50), 75% (B75), and 100% (B100) biodiesel. Samples were then collected using a dilution source sampler to simulate atmospheric dilution. Diluted and aged exhaust was analyzed for particle mass and size distribution, PM_2.5 particle mass, PM_2.5 organic and elemental carbon, and speciated organic compounds. PM_2.5 mass emissions rates for the B25, B50, and B75 soybean oil biodiesel mixtures had 20%–30% lower emissions than the petroleum diesel, but B100 emissions were about 40% higher than the petroleum diesel. The trends in mass emission rates with the increasing biodiesel content can be explained by a significant decrease in elemental carbon (EC) emissions across all blending ranges and increasing organic carbon (OC) emissions with pure biodiesel. Beef tallow biodiesel blends showed similar trends. Nevertheless, it is important to note that the study measurements are based on low dilution rates and the OC emissions changes may be affected by ambient temperature and different dilution conditions spanning micro-environments and atmospheric conditions. The results show that the use of biodiesel fuel for economic or climate change mitigation purposes can lead to reductions in PM emissions and a co-benefit of EC emission reductions. Detailed speciation of the OC emissions were also examined and are presented to understand the sensitivity of OC emissions with respect to biodiesel fuel blends.

Copyright 2012 American Association for Aerosol Research     

Characterization of Fine Particulate Emissions from Casting Processes

Fine particle (PM_2.5) emission rates and compositions from gray iron metal casting foundry were characterized for No-Bake molds poured at the Research Foundry located at Technikon, LLC (McClellan, CA). For each mold, PM_2.5 was collected for chemical analysis, and particle size distributions were measured by an Electrical Low Pressure Impactor (ELPI) to understand PM emissions during different part of the casting process. Molds prepared with phenolic urethane binders were poured with Class 30 gray cast iron at 1,427–1,480°C. PM_2.5 was collected from the pouring, cooling, and shakeout processes for each mold. Most of the PM_2.5 mass emitted from these processes was composed of carbonaceous compounds, including 37–67% organic carbon (OC) and 17–30% elemental carbon (EC). Oxides of aluminum (Al), silicon (Si), calcium (Ca), and iron (Fe) constituted 8–20% of PM_2.5 mass, and trace elements (e.g., K, Ti, Mn, Cu, Zn, and Pb) contributed 3–6%. Chemical abundances in PM were different between pouring and shakeout for each discrete mold. PM_2.5 mass emissions from pouring were 15–25% of the total from each discrete mold. Ultrafine particles (< 0.1 μm) contributed less than 1% of PM_2.5 mass, but nearly all of the particle numbers. Different mechanisms for pouring and shakeout result in variations in chemical abundances and particle size distributions. The highest PM_2.5 mass and number concentrations were observed when shakeout started. PM_2.5 size distributions in mass concentration during shakeout contained particles in the tail of coarse particles (1.6–2.5 μm) and a vapor condensation mode (0.65–1.6 μm). Flame conditions, vaporization, thermal decomposition of organic materials, and the variability of mold breakup during shakeout affect PM emission rates. A detailed chemical speciation for size-segregated PM samples at different process points needs to be conducted at full-scale foundries to obtain emission factors and source profiles applicable to emission inventories, source receptor modeling, and implementation of emission standards.     

Spatio-temporal variability in atmospheric abundances of EC,OC and WSOC over Northern India

The atmospheric abundances of elemental carbon (EC), organic carbon (OC) and water-soluble organic carbon (WSOC) have been measured in aerosol samples collected during wintertime (December–March) from selected sites (urban, rural and high-altitude) in northern India. A characteristic feature of their abundance pattern, at urban sites, is reflected in the OC/EC ratios (range: 2.4–14.5, Av=7.8±2.4, n=77) indicating dominant contribution from biomass burning sources (wood-fuel and agriculture waste). This is in sharp contrast to the OC/EC ratios at a rural site (range: 2.1–4.0, Av=3.1±0.6, n=7) influenced by emissions from coal-fired industries. The long-term measurements made from a high-altitude site (～2000 m amsl) reveal significantly lower abundances of EC and OC; suggesting that boundary layer dynamics (during wintertime) play an important role in efficient trapping of pollutants within the Indo-Gangetic Plain (northern India). The WSOC/OC ratios are fairly uniform (～0.35) in aerosols over urban sites but relatively enhanced contribution of WSOC and higher ratios (～0.5) at a high-altitude site emphasizes the significance of secondary organic aerosols. The comprehensive data set on EC, OC and WSOC/OC ratios from northern India is crucial to improve model parameterization of carbonaceous aerosols for atmospheric scattering and absorption of solar radiation on a regional scale.     

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

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

Using ATOFMS to Determine OC/EC Mass Fractions in Particles

Historically, obtaining quantitative chemical information using laser desorption ionization mass spectrometry for analyzing individual aerosol particles has been quite challenging. This is due in large part to fluctuations in the absolute ion signals resulting from inhomogeneities in the laser beam profile, as well as chemical matrix effects. Progress has been made in quantifying atomic species using high laser powers, but very few studies have been performed quantifying molecular species. In this study, promising results are obtained using a new approach to measure the fraction of organic carbon (OC) associated with elemental carbon (EC) in aerosol particles using single particle laser desorption ionization. A tandem differential mobility analyzer (TDMA) is used to generate OC/EC particles by size selecting EC particles of a given mobility diameter and then coating them with known thicknesses of OC measured using a second DMA. The mass spectra of the OC/EC particles exiting the second DMA are measured using an ultrafine aerosol time-of-flight mass spectrometer (UF-ATOFMS). A calibration curve is produced with a linear correlation (R² = 0.98) over the range of OC/EC ion intensity ratios observed in source and ambient studies. Importantly, the OC/EC values measured in ambient field tests with the UF-ATOFMS show a linear correlation (R² = 0.69) with OC/EC mass ratios obtained using semi-continuous filter based thermo-optical measurements. The calibration procedure established herein represents a significant step toward quantification of OC and EC in sub-micron ambient particles using laser desorption ionization mass spectrometry.     

Variability of Particle Number,Black Carbon,and PM10, PM2.5, and PM1 Levels and Speciation: Influence of Road Traffic Emissions on Urban Air Quality

Measurements of particle number concentration (N), black carbon (BC), and PM ₁₀ , PM _2.5 , and PM ₁ levels and speciation were carried out at an urban background monitoring site in Barcelona. Daily variability of all aerosol monitoring parameters was highly influenced by road traffic emissions and meteorology. The levels of N, BC, PM _X , CO, NO, and NO ₂ increased during traffic rush hours, reflecting exhaust, and non-exhaust traffic emissions and then decreased by the effect of breezes and the reduction of traffic intensity. PM _2.5–10 levels did not decrease during the day as a result of dust resuspension by traffic and wind. N showed a second peak, registered in the afternoon and parallel to O ₃ levels and solar radiation intensity, that may be attributed to photochemical nucleation of precursor gases. An increasing trend was observed for PM ₁ levels from 1999 to 2006, related to the increase in the traffic flow and the diesel fleet in Barcelona. PM composition was highly influenced by road traffic emissions, with exhaust emissions being an important source of PM ₁ and dust resuspension processes of PM _2.5–10 , respectively.     

Comparison of particle emissions from an engine operating on biodiesel and petroleum diesel

Biodiesel is an alternative fuel with growing usage in the transportation sector. To compare biodiesel and petroleum diesel effects on particle emissions, engine dynamometer tests were performed on a Euro II engine with three test fuels: petroleum diesel (D), biodiesel made from soy bean oil (BS) and biodiesel made from waste cooking oil (BW). PM_2.5 samples were collected on Teflon and quartz filters with a Model 130 High-Flow Impactor (MSP Corp). Organic (OC) and elemental (EC) carbon fractions of PM_2.5 were quantified by a thermal-optical reflectance analysis method and particle size distributions were measured with an electrical low pressure impactor (ELPI). In addition, the gaseous pollutants were measured by an AMA4000 (AVL Corp). The biodiesels were found to produce 19-37% less and 23-133% more PM_2.5 compared to the petroleum diesel at higher and lower engine loads respectively. On the basis of the carbon analysis results, the biodiesel application increased the PM_2.5 OC emissions by 12-190% and decreased the PM_2.5 EC emissions by 53-80%, depending on the fuel and engine operation parameters. Therefore OC/EC was increased by three to eight times with biodiesel application. The geometrical mean diameter of particles from biodiesels and petroleum diesel had consistent trends with load and speed transition. In all the conditions, there is a shift of the particles towards smaller geometric mean diameter for the biodiesel made from waste oil.     

Tailpipe emission characteristics of PM2.5 from selected on-road China III and China IV diesel vehicles

Eighteen China III and IV diesel vehicles, including light-duty diesel trucks (LDDTs), medium-duty diesel trucks (MDDTs), heavy-duty diesel trucks (HDDTs) and buses, were tested with real-world measurements using a portable emission measurement system (PEMS). The emission factors (EFs), chemical components and surface morphology of emitted particles from these vehicles were characterized. Measured features included organic carbon (OC), elemental carbon (EC), water soluble ions (WSIs) and trace elements of PM_2.5. The modelling system MOtor Vehicle Emission Simulator (MOVES) was also employed to estimate the PM_2.5 EFs from these vehicles. Carbonaceous content made up 35.8–110.8% of PM_2.5, the largest contribution of all the determined chemical components; WSIs and elements accounted for less than 10%. The average PM_2.5 EFs of MDDTs and HDDTs were 0.389 g·km^?1 and 0.115 g·km^?1, respectively, approximately one order of magnitude higher than that of LDDTs. The PM_2.5 EFs of China III buses were much lower than those of China III MDDTs and HDDTs, indicating that the inspection maintenance program (I/M) system was carried out effectively on public diesel vehicles. Moreover, the chemical composition of 9.2–56.2% of the PM_2.5 mass emitted from China IV diesel trucks could not be identified in the present study. It was possible this unidentified mass was particle bound water, but this hypothesis should be confirmed with further measurements. The SEM images of PM_2.5 samples presented a loose floc structure. In addition, the trends of variation of estimated PM_2.5 EFs derived from the MOVES simulation were essentially consistent with those of tested values.

Copyright © 2018 American Association for Aerosol Research     

Investigating the dependence of light-absorption properties of combustion carbonaceous aerosols on combustion conditions

We performed controlled combustion experiments to investigate the dependence of the mass absorption cross-section (MAC) and absorption Ångström exponent (AAE) of combustion carbonaceous aerosol emissions on combustion conditions. Using benzene and toluene as fuels, we obtained a wide range of combustion conditions by varying the combustion temperature and equivalence ratio. We also used nitrogen as a passive diluent to tune the combustion conditions. We calculated MAC and AAE from multi-wavelength light-absorption measurements using a photoacoustic spectrophotometer and aerosol mass loadings estimated from thermal-optical analysis. Starting with relatively low-temperature and fuel-rich combustion conditions and progressively increasing the temperature and/or decreasing the equivalence ratio, we produced emissions with progressive change from weakly absorbing brown carbon (BrC) (MAC at 532?nm (MAC₅₃₂) = 0.24?m²/g and AAE = 8.6) to strongly absorbing BrC (MAC₅₃₂ = 2.1?m²/g and AAE = 3.1) to mixtures of black carbon (BC) and strongly absorbing BrC (MAC₅₃₂ = 7.7?m²/g and AAE = 1.5). These findings indicate that combustion conditions are important in dictating the light-absorption properties of the emitted aerosols. Furthermore, regardless of fuel type and combustion conditions, the emitted aerosols exhibit a unified continuum of light-absorption properties that can be characterized by MAC₅₃₂ and AAE pairs. The MAC₅₃₂ and AAE pairs are well-correlated with the elemental carbon-to-organic carbon ratio (EC/OC), which is a proxy of combustion conditions, confirming previous findings that EC/OC is a practical basis for parameterizing the light-absorption properties of combustion carbonaceous aerosols.

Copyright © 2019 American Association for Aerosol Research