UNITED STATES ENVIRONMENTAL PROTECTION AGENCY f. RESEARCH TRIANGLE PARK. NC 27711 OFFICE OF AIR QUALITY PLANNING AND STANDARDS Technical Note- Clarifications and Guidance on Gaseous Pollutant Methods 01/30 /2018 During recent revisions to the QA Regulations (March 2016) and the QA Handbook (January 2017), EPA has received questions from the monitoring community on a few topics that will be addressed in this technical memo. OAQPS and ORD both agree with the clarifications and guidance below and will eventually reflect this information in future method revisions. These clarifications and guidance are effective immediately. Concentration Requirement for NO Cylinder Standards The N02 method, 40 CFR Part 50 Appendix F Section 1.3.1 requires a "gas cylinder standard containing 50 to 100 ppm NO in N2 with less than 1 ppm N02." This method has not been revised in some time and there are NIST traceable standards lower than 50 ppm NO in N2 on the market that are now suitable for use in this method. Therefore, lower standards that are NIST traceable may be used for calibrations. Concentration Requirement for S02 Cylinder Standards The S02 method, 40 CFR Part 50 Appendix A-l Section 4.1.6.1 requires a "S02gas concentration transfer standard having a certified S02 concentration of not less than 10 ppm, in N2, traceable to a NIST Standard Reference Material (SRM)". This method has not been revised in some time and there are NIST traceable standards lower than 10 ppm in N2 on the market that are now suitable for use in this method. Therefore, lower standards that are considered EPA protocol gas and NIST traceable may be used for calibrations. The transfer standard requirements for calibrations do not apply to the standards used for the 1-point QC checks or annual performance evaluations and therefore, lower concentration standards can be used for these checks as long as the gasses used are EPA protocol gas and NIST traceable. Calibration Acceptance Criteria Language For the 03 (40 CFR part 50 App D Sec 4.5.5.6), S02 (40 CFR Part 50 App C Sec. 4.2.9) and CO (40 CFR Part 50 App C Sec 4.4.7) methods, the following sentence can be found: "Compute (or calculate) the linear regression slope and intercept and plot the regression line to verify that no point deviates from this line by more than 2 percent of the maximum concentration tested" The CFR criteria could be interpreted that you can take the highest test concentration (for example 400 ppb for ozone with full scale at 500 ppb) and take 2 percent of that value (8 ppb) and allow every calibration point to diverge from the calibration line by 8 ppb. Since 2008, the QA Handbook has guidance that suggests: ------- "For the gaseous pollutants the verification/calibration is considered acceptable if all calibration points fall within 2% of the full scale, best fit straight line. In this case, all calibration points are used to develop the calibration regression line. Once the line is developed no individual point may deviate from the line by two percent. In addition, because the Handbook allows for calibrations at lower concentrations than full scale1, EPA will be adding a 1.5 ppb difference for 03, S02 and N02 and 0.03 ppm CO difference acceptance criteria for those monitoring organization that plan to calibrate at lower concentrations. If either acceptance criteria pass, the calibration will be acceptable. EPA suggests that monitoring organizations use the Handbook language. N02 Dynamic Parameter Specifications (40 CFR Part 50 Appendix F Sec 1.4) Monitoring organization have found it difficult to meet both the residence times and dynamic parameter requirements when calibrating or auditing at lower levels. 1.4 Dynamic parameter specification. 1.4.1 The O3 generator air flowrate (Fo) and NO flowrate (Fno) must be adjusted such that the following relationship holds: Pr = [NO] rc x tR > 2.75 ppm-minutes t„ = —— < 2 minutes where: Pr = dynamic parameter specification, determined empirically, to insure complete reaction of the available O3, ppm-minute [NO] rc - NO concentration in the reaction chamber, ppm tR = residence time of the reactant gases in the reaction chamber, minute [NO]std = concentration of the undiluted NO standard, ppm Fno = NO flowrate, scm3/min Fo = O3 generator air flowrate, scm3/min Vrc = volume of the reaction chamber, scm3 With the allowance of a lower the gas standard (20 ppm NO), ORD demonstrated their calibration system in the following configurations (see Figure 1.) can meet the residence times and the dynamic parameter specifications. Therefore, with the ability to use lower concentration gas standards these parameters can be met. However, as the method gets reviewed, ORD will review the requirements for the dynamic parameter specification. 1 The QA Handbook is using the term "calibration scale" to denote a range for calibration based on routine concentrations measured at monitoring organization sites. ------- Figure 1. Dynamic parameter and residence time information NO cone PPB 200 200 400 400 500 500 03 cone PPB 180 10 300 10 400 10 F NO SCCM 84.5 84.8 169.1 169.2 210.5 210.5 Fo SCCM 129 27.8 129.1 27.8 129 27.8 FZA-Act LPM 8.31 8.42 8.24 8.34 8.2 8.3 Minutes 0.627635 1.190053 0.449363 0.680203 0.394698 0.562316 [ N 0 ] RC 7.915691 15.06217 11.34138 17.17766 12.40059 17.66681 Pr ppm/Min 4.968162 17.92478 5.096395 11.6843 4.894489 9.934335 PR must be >2.75 ok ok ok ok ok ok ^rc (cm 3) [ N 0] STD 134 20 ppm ------- |