1. 6. Code of Federal Regulations; 40 CFR 50, Appendix L; p 38720.
2. 7. Recommended Reference Materials for the Realization of Physiochemical Properties; Marsh, K.N., Ed.; Blackwell Scientific: Oxford, 1987.
3. 8. Summary of Guidance; Filter Conditioning and Weighing Facilities and Procedures for PM25 Reference and Class I Equivalent Methods; U.S. Environmental Protection Agency: Research Triangle Park, NC, 1998; http://www.epa.gov/ttnamti1/files/ambient/pm25/qa/balance.pdf.
4. 9. PM25 Mass Weighing Laboratory Standard Operating Procedures for the Performance Evaluation Program; U.S. Environmental Protection Agency: Research Triangle Park, NC, 1998; http://www.epa.gov/ttnamti1/files/ambient/pm25/qa/peplsop.pdf.
5. 10. EPA/Harvard Center for Ambient Particle Health Effects. Gravimetric Analysis Round Robin Program; Boston, MA, Nov 28, 2000.