Grantee Research Project Results
2007 Progress Report: Measurement, Modeling and Analysis Methods for Airborne Carbonaceous Fine Particulate Matter (PM2.5)
EPA Grant Number: R831086Title: Measurement, Modeling and Analysis Methods for Airborne Carbonaceous Fine Particulate Matter (PM2.5)
Investigators: Chow, Judith C. , Chen, Lung-Wen Antony , Watson, John L. , Arnott, William P. , Barber, Peter W. , Moosmuller, Hans
Current Investigators: Chow, Judith C. , Chen, Lung-Wen Antony , Watson, John L. , Arnott, William P. , Barber, Peter W. , Paredes-Miranda, Guadalupe , Moosmuller, Hans
Institution: Desert Research Institute
EPA Project Officer: Chung, Serena
Project Period: September 1, 2003 through August 31, 2006 (Extended to August 31, 2008)
Project Period Covered by this Report: September 1, 2006 through August 31,2007
Project Amount: $449,456
RFA: Measurement, Modeling, and Analysis Methods for Airborne Carbonaceous Fine Particulate Matter (PM2.5) (2003) RFA Text | Recipients Lists
Research Category: Air , Air Quality and Air Toxics , Particulate Matter
Objective:
The overall objectives for this project are to: 1) reconcile different thermal/optical methods by determining factors that influence organic carbon (OC) and elemental carbon (EC) measurement; 2) specify how optical properties differ and change between particles in the air, particles on a filter, and particles undergoing changes owing to thermal analysis; 3) quantify differences in thermal carbon fractions determined by commonly used thermal and optical analysis methods; and 4) optimize thermal and optical monitoring methods to meet multiple needs of health, visibility, global climate, and source apportionment.
Progress Summary:
Laboratory analysis of standard source samples generated using DRI (see 2006 progress report) and other dilution tunnels (e.g., Lipsky and Robinson, 2006) indicate the influence of organic sampling artifact on thermal/optical OC and EC measurement. The artifact results from the adsorption of organic vapors on quartz-fiber filters (positive artefact) or volatilization of particles after they are collected on filters (negative artefact). The sampling artefact likely spread through a filter rather than only on the filter surface, and therefore causing different reflectance and transmittance OC/EC split point (Chen et al., 2004). A more quantitative assessment was conducted of this influence on both ambient and source samples. Approaches include:
- Analyze existing databases on field blanks and backup filters from the IMPROVE, CSN (Chemical Speciation Network, including the Speciation Trends Network [STN]), and SEARCH (Southeastern Aerosol Research and Characterization) networks to evaluate magnitudes and variability of adsorbed carbon in different carbon fractions and determine how they differ by location, season, and sampling configuration.
- Compare the magnitudes of sampling artifacts estimated by different methods, such as field blank, quartz behind Teflon (QBT) or quartz behind quartz (QBQ), sliced top and bottom half of the front filter, and regression methods.
- Perform laboratory analyses on selected archived samples to determine the homogeneity of adsorbed organic gases within a filter, relationships between artifacts on front and backup filters, and on the bottom half of the front filters.
- Identify the adsorbed organic species composition on front and backup filters by exploratory chemical analysis.
- Examine the influence of water-soluble organics as powders and in solution on the blank/backup filters and the quantification of OC and EC with the IMPROVE and STN/CSN thermal/optical protocols.
The IMPROVE, CSN, and SEARCH networks have been using different sampling configurations. For field blanks, which accompany sample filters to the field and are intended to emulated their passive adsorption, only the IMPROVE network provides a long enough passive exposure period to fulfill the purpose. Based on both the network averages and collocated-site studies, IMPROVE field blank TC (or OC) are generally in the range of 2.0 – 2.5 μg/cm2, while STN/CSN and SEARCH field blanks are below or close to 1 μg/cm2. The limited exposure times in the STN/CSN and SEARCH networks are 1 – 15 minutes, compared to 7 days in the IMPROVE network, which resulted in lower field blank values. This is supported by the similar CSN field and trip blank TC and OC concentrations (within ± 5% for site averages). Regression analysis suggests that CSN field blanks could under-represent the organic artifact by up to 34% (e.g., at Fresno, CA), if IMPROVE field blanks fully represent the artifact.
Fourteen of the IMPROVE samples that contain front and backup filters were sliced and weighed, with their top- and bottom-halves analyzed separately for carbon fractions. Once the filter substrate is saturated, the distribution of adsorbed organic vapors should be uniform, i.e., the top-half (QFtop) of a blank filter should yield the same OC as the bottom half (QFbott). Otherwise, the distribution of SVOC, particularly the negative OC artifact, within a front or backup filter may be described by a gradient (i.e., decreasing with the increasing penetration depth). Therefore, the OC artifact from high to low should follow the sequence of: QFbott > QBQtop > QBQbott > blank QF > blank QBQ. Sample QFbott contains higher OC and TC concentrations than the top and bottom halves of the QBQ filters in terms of μgC per mg filter. The difference is more pronounced for higher-temperature carbon fractions (e.g., OC3, OC4), especially when the QF OC loading is high. This could be explained by inhomogeneous negative OC artifact. The differences between QBQtop and QBQbott are not significant for all carbon fractions, which supports the saturation assumption with respect to organic vapor adsorption and the positive OC artifact.
The Thermal-Desorption GC/MS analysis (Ho and Yu, 2004) of front (QF) and QBQ filters indicate that most of the PAHs remain on the front filter, especially for some winter samples impacted by wood smoke where their concentration densities are highest. The n-alkanes up to octacosane (n-C28) show large fractions of the total on backup filters, often at levels twice that of the concentration density on the front filter. Higher n-alkanes (e.g., > n-C35, pentatriacontane) are rarely detected on the backup filters. Hopanes and steranes, which are believed to derive from engine lubricating oils (Fujita et al., 2007a; 2007b), did not show high levels on the backup filters even when they were detected on the front filters. Front filter concentration densities were low for these non-urban samples. Methyl-alkanes, branched-alkanes, alkenes, and pthalates were not detected at high levels during winter and had variable ratios of backup to front filter densities. Summer samples generally showed higher backup to front filter concentration densities for these organic compound categories, especially for n-alkanes, but there is much variability among the samples. There might be more evaporation of these compounds (i.e., negative OC artifact) from the front filter during the summer than during winter owing to the higher daytime temperatures.
This study also demonstrates that sampling artifact could influence the OC/EC split and therefore EC quantification. Liquid levoglucosan solution was added to diesel soot samples to simulate organic sampling artifact spreading throughout the filter. EC concentrations were not increased significantly for either the IMPROVE_A or STN/CSN carbon analysis protocols, but the change of filter reflectance and transmittance during thermal analysis reflects the abundance and distribution of light-absorbing material (EC and OP) in the filter. A two-stream radiative transfer model was used to estimate the depth of layer containing light-absorbing material relative to the whole filter. For a pure diesel soot sample, this layer is ~39% of the whole filter throughout the IMPROVE_A thermal/optical analysis, whereas after liquid levoglucosan doping the layer varies from 48 – 86% of the whole filter (i.e., light absorbing material spreads through the whole filter). Observational and model investigations suggest that within-filter char occurs, altering the reflectance/transmittance relationship. Substantial EC was reported on the bottom slices of quartz-fiber front filter samples, which are not supposed to contain EC at all: evidence that a fraction of within-filter char is mistaken as EC by transmittance correction or that the liquid spiking carried some existing particles deeper into the filer. It should be noted that no interference to the reflectance-transmittance relationship is observed when charring occurs on the filter surface, where EC resides. Diesel soot samples and diesel soot/solid levoglucosan (by resuspension onto the existing diesel sample filters) yield the same EC as the pure diesel soot samples (within 1 and 10% for the IMPROVE_A and STN/CSN carbon analysis protocols, respectively).
Future Activities:
- Improve the current optical model to consider the morphology, internal mixing, and fractal dimension of carbonaceous aerosols. Examine the relative importance of these factors with respect to the quantification of EC.
- Literature review for brown carbon definition, properties, and collection methods.
- Obtain natural and artificial brown carbon samples (e.g., from wood burning, forest fires, and humic acid) and compare the abundances of their carbon fractions.
- Estimate amount of HULIS, WSOC, and brown carbon in these samples and backup filters (possibly by HPLC, TOC, and spectral analysis methods).
- Evaluate the influence of brown carbon on thermal/optical analysis under various conditions.
References:
Chen, L.-W.A.; Chow, J.C.; Watson, J.G.; Moosmüller, H.; and Arnott, W.P. (2004). Modeling reflectance and transmittance of quartz-fiber filter samples containing elemental carbon particles: Implications for thermal/optical analysis. J. Aerosol Sci., 35(6):765-780.
Fujita, E.M.; Campbell, D.E.; Arnott, W.P.; Chow, J.C.; and Zielinska, B. (2007a). Evaluations of the chemical mass balance method for determining contributions of gasoline and diesel exhaust to ambient carbonaceous aerosols. J. Air Waste Manage. Assoc., 57(6):721-740.
Fujita, E.M.; Zielinska, B.; Campbell, D.E.; Arnott, W.P.; Sagebiel, J.C.; Mazzoleni, L.; Chow, J.C.; Gabele, P.A.; Crews, W.; Snow, R.; Clark, N.N.; Wayne, W.S.; and Lawson, D.R. (2007b). Variations in speciated emissions from spark-ignition and compression-ignition motor vehicles in California's south coast air basin. J. Air Waste Manage. Assoc., 57(6):705-720.
Ho, S.S.H.; and Yu, J.Z. (2004). In-injection port thermal desorption and subsequent gas chromatography-mass spectrometric analysis of polycyclic aromatic hydrocarbons and n-alkanes in atmospheric aerosol samples. J. Chromatogr. A, 1059(1-2):121-129.
Lipsky, E.M.; and Robinson, A.L. (2006). Effects of dilution on fine particle mass and partitioning of semivolatile organics in diesel exhaust and wood smoke. Environ. Sci. Technol., 40(1):155-162.
Journal Articles on this Report : 6 Displayed | Download in RIS Format
Other project views: | All 108 publications | 32 publications in selected types | All 29 journal articles |
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Chow JC, Watson JG, Lowenthal DH, Chen LWA, Zielinska B, Mazzoleni LR, Magliano KL. Evaluation of organic markers for chemical mass balance source apportionment at the Fresno Supersite. Atmospheric Chemistry and Physics 2007;7(7):1741-1754. |
R831086 (2006) R831086 (2007) R831086 (Final) |
Exit Exit |
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Chow JC, Watson JG. Review of measurement methods and compositions for ultrafine particles. Aerosol and Air Quality Research 2007;7(2):121-173. |
R831086 (2007) R831086 (Final) |
Exit Exit |
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Chow JC. Will the circle be unbroken: a history of the U.S. National Ambient Air Quality Standards-Introduction to the 2007 critical review. Journal of the Air & Waste Management Association 2007;57(6):650-651. |
R831086 (2007) R831086 (Final) |
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Chow JC, Watson JG, Chen L-WA, Chang MCO, Robinson NF, Trimble D, Kohl S. The IMPROVE_A temperature protocol for thermal/optical carbon analysis: maintaining consistency with a long-term database. Journal of the Air & Waste Management Association 2007;57(9):1014-1023. |
R831086 (2007) R831086 (Final) |
Exit Exit |
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Chow JC, Yu JZ, Watson JG, Ho SSH, Bohannan TL, Hays MD, Fung KK. The application of thermal methods for determining chemical composition of carbonaceous aerosols:a review. Journal of Environmental Science and Health-Part A 2007;42(11):1521-1541. |
R831086 (2007) R831086 (Final) |
Exit Exit |
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Ho KF, Cao JJ, Lee SC, Kawamura K, Zhang RJ, Chow JC, Watson JG. Dicarboxylic acids, ketocarboxylic acids, and dicarbonyls in the urban atmosphere of China. Journal of Geophysical Research-Atmospheres 2007;112(D22):D22S27 (12 pp.). |
R831086 (2007) R831086 (Final) |
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Supplemental Keywords:
Thermal protocols, Optical monitoring methods, Visibility, Light-absorbing carbon, Black carbon, Elemental carbon, Organic carbon, Sampling artifact, Radiative forcing, HULIS, WSOC,, RFA, Scientific Discipline, PHYSICAL ASPECTS, Air, Ecosystem Protection/Environmental Exposure & Risk, particulate matter, Air Quality, air toxics, Environmental Chemistry, Monitoring/Modeling, Analytical Chemistry, Physical Processes, Engineering, Chemistry, & Physics, Environmental Engineering, carbon aerosols, air quality modeling, particle size, environmental monitoring, atmospheric particulate matter, atmospheric measurements, atmospheric dispersion models, particulate organic carbon, aerosol particles, atmospheric particles, mass spectrometry, analysis of organic particulate matter, chemical characteristics, PM 2.5, air modeling, air quality models, exposure, airborne particulate matter, air sampling, gas chromatography, thermal desorption, carbon particles, air quality model, emissions, particulate matter mass, ultrafine particulate matter, particle phase molecular markers, aersol particles, modeling studies, aerosol analyzers, measurement methods, exposure assessment, carbonaceous particulate matter, chemical speciation samplingProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.