The test method supports proposed, occupational exposure 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 Protection 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.

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).

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 interlaboratory data.

The test method is being applied for emission-control testing.

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 require sorbents for efficient collection.

Note 1—Sample collection and handling procedures for environmental samples differ from occupational samples. This standard addresses occupational monitoring of DPM in workplaces where diesel-powered equipment is used.

1.2 The method is based on a thermal-optical technique (1, 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. As with most instrumentation, design improvements continue to be made. Different 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 appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in 7.1.5, 8.3, and 12.12.2.