Investigation of Gaseous Criteria Pollutant Transport Efficiency as a Function of Tubing Material
Citation:
Johnson, C., A. Whitehill, R. Long, AND R. Vanderpool. Investigation of Gaseous Criteria Pollutant Transport Efficiency as a Function of Tubing Material. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-22/212, 2022.
Impact/Purpose:
Based on this study's results, EPA will propose the revision of Section 9, Appendix E of 40 CFR Part 58 to includePVDF, PTFE, and PFA as approved tubing types for regulatory sampling of all four gaseous criteria NAAQS pollutants.
Description:
Accurate determination of NAAQS pollutant concentrations requires efficient sampling and transport of the pollutants to their respective samplers for quantitative analysis. For reactive gas sampling, Section 9 of Appendix E of 40 CFR Part 58 specifies that only borosilicate glass (Pyrex®) or fluorinated ethylene propylene (FEP Teflon®) “or their equivalent” are suitable materials for sampling and transporting to FRM and FEM instruments. It also specifies that the sample residence time between the inlet probe and the analyzer cannot exceed 20 seconds. These regulatory specifications have not been updated since 1979. The purpose of this research effort was to identify alternative transport materials for sampling gaseous criteria pollutants. This laboratory study determined the transport efficiency of O3, NO2, SO2, and CO through six candidate materials at multiple pollutant concentration levels. The need to condition or passivate the tubing with the pollutant of interest was also tested. Based on a review of the literature, six tubing materials were selected for evaluation. These included three fluorinated polymer materials (PTFE, PVDF, and PFA), a non-fluorinated polymer (PVC), and two metals (316 stainless steel and Silconert-2000® coated 316 stainless steel). All tubing had a 1/4” OD and nominal 3/16” ID, and lengths of tubing were selected to provide a 20 second residence time at the tested FRM’s or FEM’s design flow rate. For each pollutant and tubing type, three replicate tests were conducted at concentrations of 20%, 50%, and 120% of the NAAQS value of greatest regulatory relevance. The predetermined acceptance criteria was a transport efficiency of 97.5% or greater (i.e., maximum loss of 2.5%), which was selected to identify potentially alternative materials to borosilicate glass and FEP Teflon®. This acceptance criterion was adopted from the through-the-probe audit program (US EPA, 2011) used for quantifying ozone line losses during field monitoring. Testing determined that O3 was the most reactive of the four gaseous NAAQS pollutants. O3 transport efficiencies for the four fluoropolymer tubing types (FEP, PTFE, PVDF, and PFA) ranged from 95.6% to 98.6% without preconditioning. SS316, SNSS, and PVC had transport efficiencies of 0%, 9.2%, and 11.1% respectively, suggesting significant losses in the tubing without preconditioning. Following conditioning of each tubing type with 450 ppb of O3 for 1 hour, the transport efficiency of the fluoropolymer tubing types increased to an average of 99.4%. The high transport efficiency of O3 through fluoropolymer tubing was repeatable and independent of O3 concentration. Conditioning of SS316 tubing and Tygon® tubing resulted in 0% transport efficiency (i.e., 100% loss) of O3 for both tubing types. The transport efficiency of O3 through conditioned SNSS tubing improved to 87.7% with conditioning but remained below the study’s 97.5% acceptance criteria. During both the unconditioned and conditioned tests, SS316, SNSS, and Tygon® test results were highly variable and dependent on the O3 concentration being tested. Unlike the tests conducted with O3, the transport efficiency of SO2, NO2, and CO through the four fluoropolymers exceeded the 97.5% acceptance criteria for transport efficiency without conditioning. The average transport efficiency of these three gases through the fluoropolymer tubing types was 99.8% and independent of test concentrations. For SS316, SNSS, and Tygon® tubing, test results with these three pollutants had higher transport efficiencies than obtained with conditioned O3 tests; although only tests conducted with CO resulted in transport efficiencies exceeding the goal of 97.5%. Based on this study’s results, EPA will propose the revision of Section 9, Appendix E of 40 CFR Part 58 to include PVDF, PTFE, and PFA as approved tubing types for regulatory sampling of all four gaseous criteria NAAQS pollutants.
URLs/Downloads:
ORD 050224 CERTIFICATION FORM.PDF (PDF, NA pp, 350.124 KB, about PDF)INVESTIGATION OF GASEOUS CRITERIA POLLUTANT TRANSPORT EFFICIENCY AS A FUNCTION OF TUBING MATERIAL.PDF (PDF, NA pp, 1733.625 KB, about PDF)