Analysis of carbonaceous aerosols: interlaboratory comparison

Abstract

Carbonaceous aerosols are present in many workplace and environmental settings. Some of these aerosols are known or suspect human carcinogens and have been linked to other adverse health effects. Exposure to diesel exhaust is of particular concern because it has been classified as a probable human carcinogen and use of diesel-powered equipment is widespread in industry. Because previously used methods for monitoring exposures to particulate diesel exhaust lack adequate sensitivity and selectivity, a new method was needed. A carbon analysis technique called the ‘thermal–optical method’ was evaluated for this purpose. In thermal–optical analysis, carbon in a filter sample is speciated as organic and elemental (OC and EC, respectively). When the thermal–optical method was initially evaluated, only one instrument was available, so interlaboratory variability could not be examined. More recently, additional instruments were constructed and an interlaboratory comparison was completed. Eleven laboratories participated in the study, including four in Europe that employ an alternative thermal technique based on coulometric detection of CO₂. Good agreement (RSDs ≤ 15%) between the total carbon results reported by all laboratories was obtained. Reasonable within-method agreement was seen for EC results, but the EC content found by the two methods differed significantly. Disagreement between the OC–EC results found by the two methods was expected because organic and elemental carbon are operationally defined. With all filter samples, results obtained with the coulometric method were positively biased relative to thermal–optical results. In addition, the alternative method gave a positive bias in the analysis of two OC standard solutions. About 52% and 70% of the carbon found in two aqueous solutions containing OC only (sucrose and EDTA, respectively) was quantified as elemental, while EC contents of about 1% and 0.1% (respectively) were found by the thermal–optical method. The positive bias in the analysis of the OC standards is attributed largely to inadequate removal of OC during the first part of the analysis; lack of correction for pyrolytically formed carbon (char) also is a factor. Results obtained with a different thermal program having a higher maximum temperature were in better agreement with the thermal–optical method.

References

1. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Diesel and Gasoline Exhausts and Some Nitroarenes. International Agency for Research on Cancer, Lyon, France, World Health Organization, 1989, vol. 46.
2. NIOSH Current Intelligence Bulletin No. 50: Carcinogenic Effects of Exposure to Diesel Exhaust, National Institute for Occupational Safety and Health, Cincinnati, OH, DHHS (NIOSH) Publication No. 88–116, 1988.
3. American Conference of Governmental Industrial Hygienists (ACGIH), Notice of Intended Changes, 1996–1997(also see draft TLV document).
4. US Environmental Protection Agency, Health Assessment Document for Diesel Emission, EPA/600/8-90/057A (External Review Draft, 1993), Office of Health and Environmental Assessment, Environmental Criteria Assessment Office, Research Triangle Park, NC, 1993.
5. California Environmental Protection Agency, Health Risk Assessment for Diesel Exhaust (Draft), Office of Environmental Health Hazard Assessment, Sacramento, CA, 1994.
6. World Health Organization, Environmental Health Criteria 171: Diesel Fuel and Exhaust Emissions, World Health Organization, Geneva, 1996.
7. Health Effects Institute, Diesel Exhaust: A Critical Analysis of Emissions, Exposure, and Health Effects, A Special Report of the Institute's Diesel Working Group, Health Effects Institute (HEI), Cambridge, MA, 1995.
8. NIOSH, Elemental Carbon (Diesel Particulate): Method 5040. in NIOSH Manual of Analytical Methods, 4th ed. (1st Supplement), ed. Eller, P. M., and Cassinelli, M. E., National Institute for Occupational Safety and Health, DHHS (NIOSH), Cincinnati, OH; Publication No. 96-135, 1996.
9. M. E. Birch and R. A. Cary, Aerosol Sci. Technol., 1996, 25, 221.
10. R. J. Countess, Aerosol Sci. Technol., 1990, 12(1), 114.
11. Sunset Laboratory, Forest Grove, OR, USA.
12. J. C. Chow, J. G. Watson, L. C. Pritchett, W. R. Pierson, C. A. Frazier and R. G. Purcell, Atmos. Environ., 27A, 1185.
13. ZH 1/120.44 ( 1995) Von der Berufsgenossenschaften anerkannte Analysenverfahren zur Feststellung der Konzentrationen krebserzeugender Arbeitstoffe in der Luft in Arbeitsbereichen. Method No. 44: Diesel Engine Emission. Carl Heymanns Verlag, Köln.
14. D. D. Zaebst, D. E. Clapp, L. M. Blade, D. A. Marlow, K. Steenland, R. W. Hornung, D. Scheutzle and J. Butler, Am. Ind. Hyg. Assoc. J., 1991, 52(12), 529.
15. NIOSH, Elemental Carbon (Diesel Particulate): Method 5040, in: NIOSH Manual of Analytical Methods, 4th ed. (2nd Supplement), ed. Eller, P. M., and Cassinelli, M. E., National Institute for Occupational Safety and Health, DHHS (NIOSH), Cincinnati, OH; 1998(prepublication copy of method available from this paper's author).