ASTM D6877 – 03

Designation: D 6877 – 03 Standard Test Method for Monitoring Diesel Particulate Exhaust in the Workplace1 This standard is issued under the fixed designation D 6877; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon (e) indicates an editorial change since the last revision or reapproval. 1. Scope 1.1 This test method covers determination of organic and elemental carbon in the particulate fraction of diesel engine exhaust, hereafter referred to as diesel particulate matter (DPM). Samples of workplace atmospheres are collected on quartz-fiber filters. The method also is suitable for other types of carbonaceous aerosols, but it is not appropriate for sampling volatile or semi-volatile components. These components re- quire sorbents for efficient collection. NOTE 1—Sample collection and handling procedures for environmental samples differ from occupational samples. This standard addresses occu- pational monitoring of DPM in workplaces where diesel-powered equip- ment is used. 1.2 The method is based on a thermal-optical technique (1, 2)2. Speciation of organic and elemental carbon is achieved through temperature and atmosphere control, and an optical feature that corrects for sample charring. 1.3 A portion of a 37-mm, quartz-fiber filter sample is analyzed. Results for the portion are used to calculate the total mass of organic and elemental carbon on the filter. The portion must be representative of the entire filter deposit. If the deposit is uneven, two or more representative portions should be analyzed for an average. Open-faced cassettes give even deposits but are often not practical. Closed-face cassettes give equivalent results if other dusts are absent. Other samplers may be required, depending on the sampling environment (2-5). 1.4 The calculated limit of detection (LOD) depends on the level of contamination of the media blanks (5). A LOD of approximately 0.2 µg carbon per cm2 of filter was estimated when analyzing a sucrose standard solution applied to filter portions cleaned immediately before analysis. LODs based on media blanks stored after cleaning are usually higher. LODs based on a set of media blanks from a commercial laboratory were OC = 1.2 µg/cm2, EC = 0.4 µg/cm2, and TC = 1.3 µg/cm2, where OC, EC, and TC refer to organic, elemental, and total carbon, respectively. 1.5 OC-EC methods are operational, which means the analytical procedure defines the analyte. The test method offers greater selectivity and precision than thermal techniques that do not correct for charring of organic components. The analysis method is simple and relatively quick (about 15 min). The analysis and data reduction are automated, and the instrument is programmable (different methods can be saved as methods for other applications). 1.6 A method (5040) for DPM based on thermal-optical analysis has been published by the National Institute for Occupational Safety and Health (NIOSH). Method updates (3, 4) have been published since its initial (1996) publication in the NIOSH Manual of Analytical Methods (NMAM). Both OC and EC are determined by NMAM 5040. An EC exposure marker was recommended because EC is a more selective measure of exposure. A comprehensive review of the method and rationale for selection of an EC marker are provided in a recent Chapter of NMAM (5). 1.7 The thermal-optical instrument required for the analysis is manufactured by a private laboratory.3 As with most instru- mentation, design improvements continue to be made. Differ- ent laboratories may be using different instrument models. 1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety and health practices and determine the applica- bility of regulatory limitations prior to use. Specific precau- tionary statements are given in 7.1.5, 8.3, and 12.12.2. 2. Referenced Documents 2.1 ASTM Standards: D 1356 Terminology Relating to Sampling and Analysis of Atmospheres4 3. Terminology 3.1 Definitions: 3.2 For definitions of terms used in this practice, refer to Terminology D 1356. 1 This test method is under the jurisdiction of ASTM Committee D22 on Sampling and Analysis of Atmospheres and is the direct responsibility of Subcom- mittee D22.04 on Workplace Atmospheres. Current edition approved May 10, 2003. Published June 2003. 2 The boldface numbers in parentheses refer to references at the end of this test method. 3 The carbon analyzer used in the development and performance evaluation of this test method was manufactured by Sunset Laboratory, 2017 19th Avenue, Forest Grove, Oregon 97116, which is the sole source of supply of the instrument known to the committee at this time. If you are aware of alternative suppliers, please provide this information to ASTM Headquarters. Your comments will receive careful consideration at a meeting of the responsible technical committee which you may attend. 4 Annual Book of ASTM Standards, Vol 11.03. 1 Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States. 3.3 limit of detection, LOD—A value for which exceedence by measured mass indicates the presence of a substance at given false-positive rate: 3 3 estimated standard deviation of estimated mass. 3.4 Definitions of Terms Specific to This Standard: 3.4.1 organic carbon (OC)—Carbon volatilized in helium while heating a quartz-fiber filter sample to 870°C. Includes carbonates, if present, unless quantified separately. Also in- cludes char formed during pyrolysis of some materials. 3.4.2 elemental carbon (EC)—Excluding char, light- absorbing carbon that is not removed from a filter sample heated to 870°C in an inert atmosphere. 3.4.3 total carbon (TC)—Sum of organic and elemental carbon. 3.4.4 thermogram—Digitized output signal of thermal- optical instrument. Shows detector and filter transmittance signals at different temperatures in nonoxidizing and oxidizing atmospheres. 3.5 Symbols and Abbreviations: 3.5.1 DPM—diesel particulate matter 3.5.2 LOD (µg/cm2)—limit of detection: 3 3 sw 3.5.3 sw(µg/cm2)—estimate of sw 3.5.4 sw(µg/cm2)—standard deviation in collected mass loading determination 3.5.5 OC, EC, TC (µg/cm2 or µg)—organic, elemental, and total carbon 3.5.6 RSD—relative standard deviation 3.5.7 V (L)—sampled volume 3.5.8 Wb(µg)—field blank filter’s EC mass reading 3.5.9 WEC(µg)—active filter’s EC mass reading 4. Summary of Test Method 4.1 The thermal-optical analyzer has been described previ- ously (1-5). Design improvements have been made over time, but the operation principle remains unchanged. OC-EC quan- tification is accomplished through temperature and atmosphere control. In addition, the analyzer is equipped with an optical feature that corrects for the char formed during the analysis of some materials. Optical correction is made with a pulsed diode laser and photodetector that permit continuous monitoring of the filter transmittance. 4.2 The main instrument components are illustrated in Fig. 1. The instrument output, called a thermogram, is shown in Fig. 2. For analysis, a known area (normally 1.5 cm2) of the quartz-fiber filter sample is removed with a sharp metal punch. Quartz-fiber filters are required because temperatures in excess of 850°C are employed. The portion is inserted into the sample oven, and the oven is tightly sealed. The analysis proceeds in inert and oxidizing atmospheres. First, OC (and carbonate, if present) is removed in helium as the temperature is stepped to a preset maximum (about 870°C in NMAM 5040). Evolved carbon is catalytically oxidized to CO2 in a bed of granular MnO2. The CO2 is then reduced to CH4 in a Ni/firebrick methanator, and CH4 is quantified by a FID. Next, the sample oven temperature is lowered, an oxygen-helium mix (2 % oxygen after dilution of the 10 % oxygen in helium supply) is introduced, and the temperature is increased to 900°C (or higher) to remove the residual carbon. At the end of each analysis, calibration is made through automatic injection of a fixed volume of methane. 4.3 Some samples contain components (for example, ciga- rette and wood smokes) that carbonize (convert to carbon) or char in helium during the first part of the analysis. Like EC initially present in the sample, char strongly absorbs light, particularly in the red/infrared region. The char formed through pyrolysis (thermal decomposition) of these components causes the filter transmittance to decrease. Charring can begin at 300°C; the process may continue until the maximum tempera- ture is reached. After OC removal, an oxygen-helium mix is introduced to effect combustion of residual carbon, which includes char and any EC originally present. As oxygen enters the oven, light-absorbing carbon is oxidized and a concurrent increase in filter transmittance occurs. The split (vertical line prior to EC peak in Fig. 2) between OC and EC is assigned when the initial (baseline) value of the filter transmittance is reached. All carbon removed before the OC-EC split is FIG. 1 Schematic of Thermal-Optical Instrument (V = valve) for Determination of Organic and Elemental Carbon in DPM and Other Carbonaceous Aerosols. D 6877 – 03 2 considered organic; that removed after the split is considered elemental. If no char is formed, the split is assigned prior to removal of EC. Ordinarily, the split is assigned in the oxidative mode of the analysis. 4.4 Occasionally, original EC (as opposed to char) is lost with the fourth temperature step in helium. Loss of EC in helium is uncommon, but sometimes occurs, possibly due to oxidants in the sample. The OC-EC split is automatically assigned earlier (in helium) in these cases (5). 4.5 OC and EC results are reported in units µg per cm2 of filter deposit. The total OC and EC on the filter are calculated by multiplying the reported values by the deposit area (slightly less than the filter area). A homogeneous deposit is assumed. The TC in the sample is the sum of OC and EC. If carbonate is present, the carbon in it is quantified as OC unless correction is made. Additional details about carbonates are given in a following section. 5. Significance and Use 5.1 The test method supports proposed, occupational expo- sure standards (6, 7) for DPM. In the United States alone, over a million workers are occupationally exposed (8). An exposure standard for mines is especially important because miners’ exposures are often quite high. NIOSH (8), the International Agency for Research on Cancer (9) (IARC), the World Health Organization (10) (WHO), the California Environmental Pro- tection Agency (11), the U.S. Environmental Protection Agency (12) (EPA), and the National Toxicology Program (13) have reviewed the animal and human evidence. All have classified diesel exhaust as a probable human carcinogen or similar designation. 5.2 The test method provides a measure of occupational exposure to DPM. Previous studies have produced equivocal results because exposure data are lacking. Given the economic and public health impact of epidemiological studies, accurate risk assessment is critical. An ongoing NIOSH/NCI study of miners exposed to diesel exhaust should provide a more quantitative estimate of the lung cancer risk. The test method was used for exposure monitoring. Since publication (in 1996) as NMAM 5040, the method has been routinely used for occupational monitoring (5). 5.3 The test method supports a proposed EPA air standard for fine particulate carbon. Recent studies indicate a positive association between airborne levels of fine particles and respiratory illness and mortality (14-22). The test method and others have been used for EPA air monitoring networks and air pollution studies. Because different methods produce different results, method standardization is essential for regulatory compliance determinations and valid comparisons of interlabo- ratory data. 5.4 The test method is being applied for emission-control testing. 6. Interferences 6.1 EC is a more selective marker of occupational exposure than other measures of DPM (for example, particulate mass, NOTE 1—PC is pyrolytically generated carbon (char). Final peak is methane calibration peak. Carbon sources: pulverized beet pulp, rock dust (carbonate), and diesel particulate. NOTE 2—In the comparative test reported by Birch (28), participants used different maximum temperatures in helium (5). The actual maximum ranged from about 850-900°C. NMAM 5040 specifies 870°C, which is near the middle of the range. FIG. 2 Thermogram for Filter Sample Containing OC, Carbonate (CC), and EC. D 6877 – 03 3 total carbon). As defined by the test method, EC is the carbon determined during the second stage of the analysis (after pyrolysis correction). If the sample contains no pyrolyzable material, all carbon evolved during this stage is considered elemental. Inorganic dusts, carbonates, and wood and cigarette smokes ordinarily do not interfere in the EC determination (2-5). OC can be contributed by smokes, fumes and other sources. 6.2 If high levels of other dusts are present, a size classifier (for example, impactor, or cyclone, or both) should be used. If the dust is carbonaceous, a size classifier provides a more selective measure of the diesel-source OC. It also provides a better measure of the diesel-source EC if the dust contains EC (for example, carbon black, coal), which is less common. A finely ground sample of the bulk material can be analyzed to determine whether a dust poses potential interference. Depend- ing on the dust concentration, size distribution, and target analyte (EC or TC), an impactor/cyclone may required. Addi- tional details can be found elsewhere (5). Some OC interfer- ences cannot be excluded on the basis of size (for example, cigarette smoke and other combustion aerosols, condensation aerosol, fumes). 6.3 In metal and nonmetal mines, the Mine Safety and Health Administration (MSHA) recommends use of a special- ized impactor (with cyclone) to minimize collection of carbon- ates and other carbonaceous dusts (7). 6.4 For measurement of diesel-source EC in coal mines, an impactor with sub-micrometer cutpoint (7, 23, 24) must be used to minimize collection of coal dust. Only low levels of EC were found in non-dieselized coal mines when an impactor with a sub-micrometer cutpoint was used (25). 6.5 Environmental samples usually contain little (if any) carbonate. Levels in some occupational settings are quite high. Depending on the carbonate type, a carbonate-subtracted value for OC (and TC) can be obtained through acidification of the sample or separate integration of the carbonate peak (see 12.12). 7. Apparatus 7.1 The main components of the thermal-optical analyzer used in the test method are illustrated in Fig. 1. The principal components are: 7.1.1 Sample oven—temperature programmable. 7.1.2 Oxidizer oven—packed with MnO2 and heated to 860°C. 7.1.3 Methanator—packed with catalyst (Ni-coated fire- brick) and heated to 500°C. 7.1.4 FID—flame ionization detector. 7.1.5 Pulsed diode laser and photo detector—for continu- ous monitoring of filter transmittance. Warning—In accor- dance with the manufacturer, the instrument is a Class I Laser Product. Weakly scattered laser light is visible during opera- tion, but does not pose a hazard. The internal laser source is a Class IIIb product, which poses a possible hazard to the eye if viewed directly or from a mirror-like surface (that is, specular reflections). Class IIIb lasers normally do not produce a hazardous diffuse reflection. Repairs to the optical system, and other repairs requiring removal of the instrument housing, should be performed only by a qualified service technician. 7.1.6 Valve box/calibration loop—for control of gas flow and automatic injection of methane internal standard. 8. Reagents and Materials 8.1 Organic Carbon (OC) Standards—Sucrose stock solu- tion having carbon concentration of 25 mg/mL. Working standards (dilutions of stock) with concentrations of 0.1 to 3 mg C per mL solution. Ensure carbon loadings of standards spiked onto filter punches bracket the range of the samples. 8.2 Ultrapure water, Type I, (for preparation of sucrose standard solution). 8.3 Sucrose—reagent grade (99+ %). 8.4 Helium-UHP (99.999%). Scrubber also required for removal of trace oxygen. 8.5 Hydrogen—purified (99.995%). Cylinder or hydrogen generator source. Warning—Hydrogen is a flammable gas. Users must be familiar with proper use of flammable and nonflammable gases, cylinders, and regulators. 8.6 Air—Ultra zero (low hydrocarbon) 8.7 Oxygen (10 %) in helium—both gases UHP, certified mix 8.8 Methane (5 %) in helium—both gases UHP, certified mix 8.9 37-mm cassettes or alternative sampler 8.10 Personal sampling pumps 8.11 High-purity, quartz-fiber filters—pre-cleaned. High- purity, binder-free, high efficiency filters must be used.5 Pre- cleaned filters are available from several laboratories. Filters also can be purchased and cleaned in-house. Filters should be cleaned in a muffle furnace operated at 800-900°C for 1-2 hours. The filters should be checked (analyzed) to ensure that OC contaminants have been removed. A shorter cleaning period may be effective. OC results immediately after cleaning should be below 0.1 µg/cm2. OC vapors readily adsorb onto clean filters. Even when stored in closed containers, OC loadings may range from 0.5 µg/cm2-0.8 µg/cm2 after several weeks. 8.12 Aluminum foil 8.13 10-µL syringe (and other sizes, depending on volume of standard applied) 8.14 Metal punch—for removal of 1.5 cm2 filter portions NOTE 2—A smaller portion (for example, taken with cork borer) may be used, but the area must be large enough to accommodate the laser (that is, beam should pass through the sample, not around it). The area of the portion must be accurately known, and the sample must be carefully positioned (filter transmittance will decrease dramatically when the sample is properly aligned). A filter portion $0.5 cm2 with diameter or width #1 cm is recommended. 8.15 Tweezers—to handle filters 5 High filtration efficiency and filter purity are essential to the performance of the test method. Certain impurities (alkali metals) can react with quartz at elevated temperature. Impure quartz also may cause EC removal in helium. The following product was used in the evaluation of this test method: Pall Gelman Sciences Pallflex Tissuquartz 2500QAT-UP quartz-fiber filters. An equivalent product is not known to the committee at this time. If you are aware of alternative suppliers, please provide this information to ASTM Headquarters. Your comments will receive careful consideration at a meeting of the responsible technical committee which you may attend. D 6877 – 03 4 8.16 Volumetric flasks—Class A. 8.17 Analytical balance 9. Sampling 9.1 Calibrate each personal sampling pump at 1-4 L/min with a representative sampler in line. 9.2 Use tweezers to insert filter supports (a second quartz filter, cellulose pads or clean stainless steel screens) and pre-cleaned, quartz-fiber filters into sampling cassettes. Seal cassettes. A second quartz filter permits correction for adsorbed vapor (5, 26). NOTE 3—Cellulose support pads give higher OC blanks than quartz filters or stainless steel screens. Filters are less expensive than screens. 9.3 Attach sampler outlet to personal sampling pump with flexible tubing. Remove plug from cassette inlet, if present. 9.4 Sample at an accurately known flow rate. 9.5 After sampling, replace top piece of cassette (or other- wise protect sample), if removed, and pack securely for shipment to laboratory. NOTE 4—DPM samples from occupational settings