CSTL Program: Environmental Measurements

Production of SRM 2784: Filter-Based Fine Particulate Material

George A. Klouda, James J. Filliben (898), Helen J. Parish (SRI International) and Judith C. Chow (Desert Research Institute)

Abstract. SRM 2784 urban dust on quartz-fiber filter will be a Standard Reference Material designed for the evaluation of analytical methods used to characterize the carbon composition of atmospheric fine particulate matter (PM2.5, having diameters nominally less than 2.5 micrometers) for national air quality monitoring programs. Since attempts to collect enough contemporary urban dust for this SRM had been faced with setbacks, production proceeded with the resuspension of the existing SRM 1649a Urban Dust to avoid further delays.  Although SRM 1649a urban dust was collected in Washington, D.C. during the 1970’s it remains a valuable material for intercomparison of methods and laboratories. The advantages of this feedstock are its immediate availability, its proven stability over time, and its known carbon composition.  SRM 2784, a fine fraction of SRM 1649a, is expected to have a chemical composition that is similar to the raw material.  Through future interlaboratory comparisons of bulk carbon, trace-carbon chemical speciation and carbon-isotope abundances, values will be assigned with the intention of certification.

Purpose. Through the Standard Materials for the PM 2.5 National Research Program, interagency agreement DW13939042-01-0 between NIST and the US EPA, SRM 2784 has been designed and produced especially for the seven EPA “Supersites” that are monitoring fine airborne particulate matter (PM) throughout the U.S.  SRM 2784 will provide the means to intercompare methods and laboratories for the measurement of black (elemental) carbon in PM. Use of this SRM will determine the level of agreement between sites and establish traceability to NIST for elemental and organic carbon measurements based on thermal-optical techniques.

Major Accomplishment.  In collaboration with DRI and SRI, this year we have tared over 2000 filters, mounted these in especially designed holders, loaded these filters with the fine fraction of SRM 1649a through a PM resuspension/size segregation/filtration system, and determined the mass loading on each filter.  We have also been able to evaluate this dust generation and collection system for producing up to 320 filters per run, allowing us to establish a method of delivering other dust materials to filters in significant number and in a timely way to benefit other scientific communities faced with issues related to fine aerosol.

Impact. The basis for effective decisions lies in the accuracy and uncertainty of measurements, and the use of SRMs strengthens those measurements used as the first link in the long chain of environmental action. In a recent round-robin intercomparison involving both the atmospheric and ocean-sciences communities, black carbon measurements varied by more than a factor of six [Currie et al., submitted to Environmental Science and Technology, 2001]. Considering the importance of black carbon measurements related to climate forcing and human respiratory/pulmonary health, SRM 2784 is expected to play an indispensable role in PM measurement quality assurance, detecting biases across methods, laboratories, and applications, and improving PM metrology.

Future Plans.  Next year, SRM 2784 will be made available after we characterize the filters for elemental carbon based on thermal-optical methods, and organize an intercomparison to access the measurement reproducibilities within and across other methods. We shall also certify this material for total carbon, and provide speciated value assignments for carbon isotopes. The technology for producing aerosol filter SRMs will be commercially developed for other areas of research, e.g., possibly bioaerosols, diesel soot and cigarette smoke for the health-sciences community.