A Quality Assurance Project Plan (QAPP) defines a project-specific quality system for planning, implementing, assessing, and reporting of environmental data collection. All Prevention of Significant Deterioration (PSD) meteorological or ambient air quality monitoring projects are required to have an approved QAPP if the data will be used to assess air quality analyses or to support New Source Review (NSR) permits. It is the responsibility of the U.S. Environmental Protection Agency (EPA) to establish the quality assurance requirements that must be followed by monitoring organizations to ensure the data collected are of sufficient quality to meet the project's objectives. Revised air quality monitoring requirements were finalized by EPA on March 28, 2016, with an effective date of April 27, 2016, as defined in Revisions to Ambient Monitoring Quality Assurance and Other Requirements (81 FR 17247).1
Since the publication of 81 FR 17247, EPA has released a series of clarifying memoranda and technical guidance to help monitoring organizations better interpret the new quality assurance requirements and quality control testing criteria for ambient monitoring programs. EPA recommends monitoring organizations review their QAPPs and standard operating procedures on a regular basis to incorporate the latest regulatory requirements for their individual monitoring network.
Reintroduction of 40 CFR Part 58 Appendix B
In revisions to EPA's ambient monitoring requirements made in 2006,2 monitoring requirements for PSD projects were combined with requirements for State and Local Air Monitoring Stations (SLAMS) networks in 40 CFR Part 58 Appendix A; Appendix B, which was previously specifically for PSD monitoring, was left reserved. The consolidation of requirements in Appendix A caused confusion among monitoring organizations regarding which requirements were meant for SLAMS and which were meant for PSD monitoring. To eliminate this confusion, EPA has reinstated Appendix B to address quality assurance activities specifically related to PSD monitoring. Many of the quality assurance requirements defined in Appendix B mimic the SLAMS requirements in Appendix A; however, there are a few differences in quality assurance activities, such as the frequency and criteria levels of performance audits and quality control testing.
Appendix B also establishes the roles of the reviewing authority over PSD monitoring programs. The reviewing authority is responsible for ensuring that the quality assurance requirements defined in the QAPP are being met by the monitoring organization. For PSD monitoring organizations, the reviewing authority is typically the state or PSD permitting agency, but there are some instances in which EPA would be the reviewing authority and work directly with the PSD monitoring organization.
One-Point Quality Control Checks for Gaseous Analyzers
In its decision on the case (U.S. Sugar v EPA, which consolidated approximately 30 challenges by industry and environmental petitioners), the court generally sided with the environmental community in vacating key elements of the rule, remanding others, and rejecting industry challenges to the energy audit requirement and handling of startups, shutdowns, and malfunctions in setting standards.
As part of the March 28, 2016 final rule (81 FR 17247), the prescribed range for one-point quality control (QC) checks of sulfur dioxide (SO2), nitrogen dioxide (NO2), and ozone (O3) was revised to concentrations between 0.005 and 0.080 parts per million (ppm), down from 0.010 to 0.100 ppm; for carbon monoxide (CO) analyzers, the range is now concentrations between 0.5 ppm and 5 ppm, down from 1.0 to 10 ppm. One-point QC checks for criteria pollutant gaseous analyzers are considered to be critical for maintaining the integrity of the measurement data. QC checks must be performed once every two weeks, with acceptance criteria of 10 percent for SO2 and CO, 15 percent for NO2, and 7 percent for O3.
EPA affirmed that the selection of the target concentration used in the QC checks should be related to the monitoring objectives and should be defined in the QAPP. For example, for monitors with an objective of measuring trace level (or background) concentrations, the concentration level for QC checks should be set to the mean or median concentrations measured at the site, while monitors used for decisions regarding compliance with National Ambient Air Quality Standards (NAAQS) or NAAQS comparability can use a practical concentration within the prescribed range, still taking into account the mean or median concentration of the monitored data. For new stations lacking previously monitored data to determine a mean or median concentration, operators should consult with the reviewing authority to establish a practical level for the QC target.
In an effort to encourage QC checks to be conducted at lower levels, EPA's Office of Air Quality Planning and Standards (OAQPS) published a technical memorandum3 on May 5, 2016, establishing a dual acceptance criteria for QC checks. The dual acceptance criteria provides monitoring organizations with the opportunity to use a percent difference criteria (as defined above) or an absolute difference criteria. EPA set the absolute difference criteria for SO2, NO2, and O3 at 0.015 ppm. Although the level of the criterion is the same for each of these pollutants, the benefit resulting from the additional leeway provided by the absolute difference method varies due to the different percentage-based criteria. The benefit of using the absolute difference is realized for target concentrations less than 0.014 ppm for SO2, 0.010 ppm for NO2, and 0.022 ppm for O3.
Annual Performance Evaluation Audits
EPA has also revised the performance evaluation (PE) audit levels in both 40 CFR Part 58 Appendix A and Appendix B for gaseous analyzers. While performance evaluations are required to be conducted annually for SLAMS monitors, performance evaluations for PSD monitors are required on a quarterly or 90-day frequency. In 81 FR 17247, EPA is requiring that performance be evaluated by challenging monitors with the audit gas standard from at least three of the ten audit levels defined in section 220.127.116.11 in both 40 CFR Part 58 Appendix A and Appendix B. The audit points are selected for an individual site or a network of sites based on the level of the instrument’s method detection limit (MDL), the 99th percentile of all concentration data collected, and either the maximum monitored concentration or the level of each pollutant's respective NAAQS.
On May 3, 2016, EPA OAQPS published a technical memo4 describing the method for choosing audit levels. The first audit level must be based on a concentration two to three times the MDL of the monitor. EPA provides two definitions for the MDL in the memo: either (1) the federal MDL of the analyzer's method, as reported to EPA's Air Quality System database; or (2) an alternative MDL if the monitoring organization has performed independent MDL determinations. Once the MDL is determined, the user must select the audit level (found in 40 CFR 58 Appendix A Section 18.104.22.168) that best represents two to three times the value of the MDL. Attachment A of the technical memo provides monitor method codes and acceptable audit levels for each type of analyzer. The remaining two audit levels required in the PE audits should be selected based on the 99th percentile of monitored concentration data collected and either the maximum concentration monitored at the site (or within a network of sites) or the NAAQS level of the pollutant, which can translate to more than one audit level (for example, NO2 has a primary one-hour and annual standard). However, due to a variety of detection methods for measuring NO2, EPA does allow auditors to use their best judgement when applying audit techniques on different types of monitors. For example, NO2 guidance documents and experience should be considered when conducting PE audits using gas-phase titration (GPT) techniques for generating NO2 concentrations.
Owners/operators at PSD sources running ambient air monitoring programs should verify that the latest monitoring requirements have been adopted in their QAPP to ensure data being collected are of sufficient quality. Meteorological Solutions Inc., a Trinity Consultants company, has implemented the changes described in the Revisions to Ambient Monitoring Quality Assurance and Other Requirements (81 FR 17247) at monitoring sites across the country. In addition to installation and operation of monitoring networks, MSI offers QAPP development, on-site training, and independent auditing services for industrial clients operating their own ambient monitoring network.
1 40 CFR Part 58, Final Rule. Revisions to Ambient Monitoring Quality Assurance and Other Requirements. See 81 Federal Register 17247 (April 28, 2016).
2 40 CFR Parts 53 and 58, Final Rule. Revisions to Ambient Air Monitoring Regulations. See 71 Federal Register 61236 (October 17, 2006).
3 U.S. EPA OAQPS, Technical Note - Guidance on Statistics for Use of 1-Point QC Checks at Lower Concentrations as described in 40 CFR Part 58 Appendix A Section 3.1.1 (May 5, 2016)
4 U.S. EPA OAQPS, Technical Note - Guidance on Identifying Annual PE Audit Levels Using Method Detection Limits and the 99th Percentile (May 5, 2016)