Quality Assurance (QA) consists of the systems and procedures designed into a program to establish quality as an inherent part of the program. Quality Control (QC) consists of the practical checks and assessments done to maintain and document the performance of measurement systems. QA procedures for the each monitoring study should include:
Although discussion of these procedures is not detailed in this document, adherence to these requirements should be required of any contractor or agency conducting one of the planned field studies. QC procedures included in this Protocol address calibration and assessment of monitoring instruments, sample collection or handling procedures, laboratory analyses, and assessments of data quality. Such procedures are based on established methods or procedures, including:
The QC procedures to be implemented in the studies conducted under this Protocol must be specified in the study-specific QAPP. Assessments of data quality must be based on data quality objectives (DQO's) established according to USEPA guidelines before any data collection takes place. The DQO process considers what quality of data is required to meet the study goals, and then sets criteria for data quality (e.g., accuracy, precision, completeness) to meet those goals.
Calibration of all monitoring and analytical equipment is essential to ensure the quality of the data collected. A multipoint calibration includes a minimum of four points (three spaced over the expected range and a zero point), generated by the calibration system. Although more points may be preferable, most current gas analyzers provide inherently linear response over their entire operating range; therefore, four points should be sufficient. Multipoint calibrations must be done prior to the analyzer being put into service and at least every 6 months thereafter. Additional calibrations should be conducted if any of the following conditions occur:
The analyzers should be calibrated in-situ without disturbing the normal sampling inlet system to the degree possible. Analyzer-specific SOPs should be developed based on the manufacturer's recommended calibration procedures. However, the following steps outline the multipoint calibration procedure for the gas analyzers. If appropriate, a NIST-traceable multicomponent gas mixture (i.e., CO, NO in N2) may be used to calibrate multiple gas analyzers.
The responses of the analyzer should be analyzed by linear regression to assess the results of the calibration. Acceptance criteria for the linear regressions are left to the discretion of the monitoring agency, but the following are suggested: slope, 1 ± 0.10; intercept, zero ± 1 x analyzer lower detectable limit (LDL) or ±1% of the tested range (whichever is greater); and correlation coefficient (r), > 0.995, where the ± values represent 95% confidence intervals. Regardless of what criteria are selected, the analyzer still must also pass audit tests, which require an absolute difference between the analyzer reading and the standard gas concentration of no more than 15 percent.
Calibration of the PM2.5 samplers includes a multi-point calibration of the sampling flow rate, as well as calibrations of the internal temperature and pressure sensors. Procedures for calibration of the PM2.5 samplers should be included in SOPs for each instrument and should be developed based on the manufacturer's recommended calibration procedures, and in compliance with the requirements of the PM2.5 Federal Reference Method.8 Additional guidance can be on calibration of PM2.5 samplers can be found in the USEPA's Quality Assurance Guidance Document 2.12: Monitoring PM2.5 in Ambient Air Using Designated Reference or Class I Equivalent Methods.11
Calibration of the aerosol monitors must be done prior to the analyzer being put into service and at least every 6 months thereafter. Additional calibrations should be conducted if any of the following conditions are met:
Calibration of the aerosol monitors (i.e., Aethalometer and BAM or TEOM) is based on the calibration of sampler. For each monitoring study conducted under this Protocol, SOPs for each of the aerosol monitors used be developed based on the manufacturer's recommended calibration procedures. In general, a NIST-certified flow transfer standard should be used accurately measure the instrumental flow rate at one or more flow settings. If differences in the measured flow rate and the displayed flow rate exist, the SOP or appropriate operator's manual should be consulted for procedures on flow rate adjustments.
Calibration of the aerosol monitors must be done prior to the analyzer being put into service and at least every 6 months thereafter. Additional calibrations should be conducted if any major maintenance activities are performed on the aerosol monitors/samplers, or if audits of the flow rate indicate differences of greater than 2% from the nominal flow rate or greater than 4% from the audit flow rate measurement.
Meteorological sensors used for the studies conducted under this Protocol should be factory calibrated prior to being put into service and every 6 months thereafter. Sensors can be calibrated in situ using a NIST-traceable transfer standard, or can be returned to the manufacturer for recalibration. If sensors are returned to the factory for calibration, the timing of the calibration should be coordinated to avoid the loss of meteorological data during integrated sampling periods. Table 6-1 presents the criteria for the meteorological sensor calibration.
Accurate analysis of the samples collected in the studies conducted under this Protocol requires the appropriate calibration of the instrumentation used for the analyses. Procedures for the calibration of these instruments are provided in the respective monitoring methods (e.g., HPLC for TO-11A, GC/MS for TO-15, analytical balance for PM2.5 FRM). These methods provide prescriptive descriptions of the requirements for instrument calibration as well as the calibration checks and other method-specific quality control requirements. Laboratories conducting these analyses for studies conducted under this Protocol should be familiar with the requirements of the respective methods and should have SOPs in place for performance of the required calibrations and calibration checks.
Traffic monitoring equipment/data provided by the State Department of Transportation or similar entity should be accompanied by the appropriate calibration records of the traffic monitoring equipment. These records along with any supporting QA/QC documentation should be reviewed by the contractor conducting the monitoring studies to insure that the use of the existing traffic monitoring equipment meets the data quality needs of the study.
If new traffic monitoring equipment must be installed for any of the studies conducted under this Protocol, the contractor conducting the monitoring study must insure that the traffic monitoring equipment is properly calibrated according to existing standards or the manufacturer's recommendations.
A variety of QC checks should be conducted in the field to ensure that the continuous monitors and the integrated sampling equipment are operating properly. In addition to QC activities conducted in the field, TO-11A, TO-15, and the PM2.5 FRM all have associated laboratory QC activities that are required. Procedures and acceptance criteria for the QC checks required for the laboratory analyses are described in the respective methods and include continuing calibration checks and analysis of blank samples. Laboratories conducting these analyses for studies conducted under this Protocol should be familiar with the requirements of the respective methods and should have SOPs in place for performance of the required QC checks. This section focuses on the QC checks to be conducted in the field.
Level 1 zero and span checks are conducted to assess if the gas analyzers are operating properly and to assess if any drift in instrument response has occurred. These checks should be conducted nightly if the calibration system/gas analyzers used can be programmed to automatically perform these checks. The Level 1 checks are conducted by challenging the analyzer first with zero air and then with a test atmosphere containing a working standard of the target gas at a concentration of between 70 percent and 90 percent of the full measurement range in which the analyzer is operating. For these checks, the challenge gas should be sampled through the entire sampling inlet system, to mimic the actual sampling of ambient air. The results of the Level 1 zero/span checks should be plotted on control charts to graphically illustrate the trends in the response of the analyzer to the challenge gases. If the measured concentrations fall outside of the control limits, the accuracy of the MFC calibration system should be checked with a NIST-traceable flow standard. If the MFC flow accuracy is confirmed, the data recorded since the previously successful Level 1 check should be flagged and the analyzer should be recalibrated using the multipoint calibration procedures described in Section 6.1.1. It is highly recommended that nightly Level 1 checks are conducted; however, if for some reason nightly Level 1 checks cannot be conducted, the precision checks described below can serve as the Level 1 checks.
At least once every 2 weeks a precision check should be conducted by challenging each gas analyzer with a known concentration of a standard gas mixture to assess the ability of the analyzers to measure a gas under reproducible conditions. The precision checks should be conducted by challenging the gas analyzer with a standard gas of known concentration. The gas must be supplied through all filters, scrubbers, and other conditioners and should be supplied through as much of the sample inlet system as possible. After completion of the precision check, the actual concentration of the working standard and the measured concentration indicated by the analyzer should be reported along with the percent difference between these values. Precision should be calculated at the end of each calendar quarter.
Leak checks of the continuous aerosol monitors and PM2.5 samples should be conducted periodically (e.g., every fifth sampling period) according to the manufacturer's recommended procedures and should meet the respective acceptance criteria. Generally, the leak checks are conducted by disconnecting the sampling line from the instrument inlet and blocking the flow of air into the inlet. The sampling pump is allowed to operate until an appropriate level of vacuum is achieved, after which the pump is turned off and the pressure in the instrument is monitored.
To pass the external leakage test, the difference between the two pressure measurements should not be greater than the number of mm Hg specified for the sampler by the manufacturer, based on the actual interior volume of the sampler, that indicates a leak of less than 80 ml/min. If a leak check fails, the appropriate operator's manual should be consulted for troubleshooting recommendations.
Field blanks provide data for evaluating contamination introduced into the samples from field activities other than sampling. Field blank should be collected and analyzed for the TO-11A and PM2.5 methods used in the monitoring studies conducted under this Protocol. Field blanks should be handled like normal samples, with the exception of not actually sampling the air. Blank DNPH samples should be collected by installing the DNPH tubes into the sampler and removing the tubes without drawing any air through the tube. PM2.5 field blanks should be collected by installing a blank filter into the PM2.5 sampler and removing it without drawing air through the filter. Blank At least 10% of all samples collected should be field blanks. The field blanks should be selected such that they represent 10% of all sample material lots purchased for the project.
Acceptance criteria for the field blanks should be established in the QAPP for each study prior to initiation of the study. Recommended acceptance criteria for the DNPH tube field blanks are:
Recommended acceptance criteria for the PM2.5 field blanks are < 30 µg change between weighings.
To ensure the data quality of the monitoring data collected during each study, a series of QA audits should be conducted. At a minimum, these audits should include performance evaluation (PE) audits, technical systems audits (TSA), and audits of data quality (ADQ).
PE samples are used to ensure the performance of the monitoring systems used to collect the pollutant and meteorological data. For the studies conducted under this Protocol, these audits involve challenging the gas monitors with a standard of known concentration, auditing the flow rates of the aerosol monitors, collocating duplicate sensors with the meteorological sensors, challenging the analytical instrumentation with standards of known concentration, and auditing the calibration of the analytical balance with standard weights. All of the PE audits should be done with standards that are independent of those used for the calibration or routine checks of the systems being audited.
For the gas analyzers, PE samples involve challenging the analyzers with standards of known concentration that are independent of those standards used to calibrate the analyzers. Generally this challenge is conducted as a blind audit, such that the site operator is not aware of the gas standard concentrations delivered to the analyzers. Clearly, the appropriate concentration values to be used for PE samples will be different for the different gases (CO, and NOx). In addition, the appropriate PE concentrations may vary with the analyzer operating range, which is selected based on the characteristics of the monitoring site. Consequently, the recommended concentration ranges for PE samples are given in Table 6-2 relative to the full scale range of the analyzer, rather than in concentration units. At least one PE sample of known concentration is to be delivered to the analyzer from each of the applicable ranges shown in Table 6-2. The indicated ranges are consistent with the requirements of 40 CFR 58, Appendix A, Section 3.2.1.
| Audit Point | Percent of Full Scale Rangea |
|---|---|
| 1 | 3 to 8 |
| 2 | 15 to 20 |
| 3 | 35 to 45 |
| 4 | 80 to 90 |
a Applies to operating range of CO or NOx analyzer.
PE sample challenges should be conducted at least quarterly on each analyzer and can be conducted (a) by a person outside of the agency or an independent QA group within the agency, or (b) by having an independent audit device, such as used in the National Performance Audit Program (NPAP), sent to the monitoring station. In the former case, an independent audit system or standard is brought to the monitoring station and used to produce working standards of the target gases that are supplied to the analyzers by the auditor. In the latter case, the audit device provided to the monitoring agency produces working standards of the calibration gases that are supplied to the analyzers. The operators and auditor do not know the concentrations of the standards that are produced by the audit equipment. Responses of the analyzers are recorded and provided to the agency that supplied the audit device. That agency compares the responses of the analyzers to the calculated concentrations from the audit device and provides an audit report to the monitoring agency. In both cases, the PE sample audit should be conducted by supplying the analyzer with the PE sample gas in its normal sampling mode such that the audit gas passes through all sample inlet components used during normal ambient sampling.
Both the actual concentration of the PE sample gases and the concentration measured by the analyzer being audited should be reported, along with the percent differences between these concentrations for each audit point. The calculated percent differences are used to confirm the analyzer precision and bias estimates obtained from routine checks.
The PE audit should also include an independent check of the gas flow controllers in the calibration system, using a NIST-traceable flow standard.
For the continuous aerosol monitors and the PM2.5 samplers, a PE audit of the sample flow rate should be conducted at least quarterly. For the aerosol monitors, the PE audit should be conducted by measuring the sample flow at the inlet of the monitor using a calibrated flow measurement device with an appropriate measurement range. The audit should be conducted at ambient temperature for readings to be valid. An STP flow device can be used if the temperature is within 5° C of 25° C; in this case skip the next step. Record the flow rate measured by the audit flow meter and the flow rate shown on the aerosol monitor display. If the audit flow meter is a volumetric standard, the measured flow rate may need to be converted to STP for comparison to the aerosol monitor. The flow rate of the aerosol monitors should agree with the audit flow rate within 4%, and within 5% of the nominal flow rate of the monitor. If the flow difference is greater than these tolerances, the operator's manual should be consulted for appropriate corrective action.
PE audits of the analytical instrumentation used for the analysis of the TO-11A and TO-15 samples should involve the analysis of blind audit samples prepared from NIST-traceable standards independent of those used for the calibration and routine QC activities for the respective instrumentation. The audit samples should have concentrations of the target analytes that are within the normal calibration range of the instrumentation and are comparable to the measured concentrations in the ambient air. These audits should be conducted at least quarterly and the acceptance criteria for these PE audits should equal those for routine calibration checks.
PE audits of the analytical balance used for the gravimetric measurements of the PM2.5 filters should be conducted at least quarterly using NIST-traceable weights that are independent of those used for the calibration and routine QC checks of the balance. For these PE audits, the balance display should agree with the designated value of the audit weight to within ±0.020 mg.
PE audits of the meteorological sensors should be conducted at least quarterly by collocating independent sensors with those installed at the monitoring stations. Acceptance criteria for these PE audits should equal those for accuracy requirements provided in Table 4-2.
Traffic monitoring equipment/data provided by State DOTs or similar entities should include records of QA/QC activities including any pertinent PE audit results. These QA/QC records along with any supporting documentation should be reviewed by the contractor conducting the monitoring studies to insure that the use of the existing traffic monitoring equipment meets the data quality needs of the study.
If new traffic monitoring equipment must be installed for any of the studies conducted under this Protocol, the contractor conducting the monitoring study must insure implement appropriate QA/QC procedures according to existing standards or the manufacturer's recommendations and conduct PE audits as warranted.
A TSA is an on-site review and inspection of the operation of an air monitoring station to assess its compliance with established QA/QC procedures and any applicable regulations. TSAs assess whether all procedures for the monitoring program are being followed and documented. A TSA should be conducted immediately before or shortly after the start of monitoring and should be repeated at least every quarter. TSAs should be performed by an independent auditor who is knowledgeable of the monitoring program but independent of routine operations.
Long term operation of continuous monitoring equipment and integrated gas sampling equipment requires a preventive maintenance program to avoid instrument down-time and data loss. Despite active preventive maintenance, occasional problems may arise with the monitors. A preventive maintenance program should be included in each of the monitoring studies conducted under this Protocol based on the recommended procedures for the equipment installed at the monitoring stations.
