By William C. Schillaci
Inaccurate Emissions Readings
Major sources of air emissions, including electric utilities, petroleum refineries, and municipal waste incinerators, may be miscalculating their releases of pollutants because of misrepresented gas cylinders used to test continuous emissions monitoring systems (CEMS).
As a result, sources in EPA’s Acid Rain Program and NOx Budget Trading Program may be certifying compliance with their emissions limits even though actual emissions may be exceeding those limits. Conversely, sources that are overestimating their limits may not be taking advantage of opportunities to sell allowances they are accumulating or may be purchasing allowances they do not need.
The cylinders—called protocol gas cylinders—contain gaseous mixtures of carbon dioxide (CO2), nitric oxide (NO), and sulfur dioxide (SO2) and are also used to monitor emissions under the national ambient air quality standards (NAAQS). In 2003, an EPA contractor estimated that utilities purchased from 37,500 to 75,000 protocol gas cylinders annually and emissions testing companies purchased 16,500 to 55,000 cylinders per year.
In a year-long investigation, EPA’s Office of the Inspector General (OIG) anonymously purchased 87 protocol cylinders within the tri-blend gas mixtures that the vendors had certified fell with the + 2 percent range required by EPA’s regulations. OIG then had the National Institute of Standards and Technology (NIST) analyze each cylinder for the three gases. OIG reported the result:
“We found that 89 percent (233 components or gases) met the Acid Rain Program’s accuracy criterion and 11 percent (28 components) did not. Of the 28 components that did not meet the criterion, 17 were within 3.0 percent of the NIST-determined true concentration; 7 were within 3.0 to 5.0 percent; and 4 exceeded the true concentration by more than 5.0 percent.”
Inaccurate calibration gases can negatively affect EPA programs that rely on accurate emissions or ambient air quality measurements. For example, if a calibration gas used by a utility was certified to contain 100 parts per million (ppm) SO2, but only contained 96 ppm, the system operator would unknowingly calibrate the CEMS to read 96 ppm as 100 ppm. This would result in the CEMS overestimating emissions. Conversely, if the true concentration of the calibration gas were more than the certified concentration, the system operator would unknowingly calibrate the CEMS to underestimate emissions.
While the range of inaccuracies in OIG’s investigation were relatively low, the cumulative result of miscalculations can be significant for both environmental reasons and the economics of major sources. For example, in 2007, 99 percent of NOx emissions measured under the NOx Budget Program were measured by CEMS. For that year approximately 700,000 NOx allowances were traded in private transactions. The price of NOx allowances varied from about $500 to $1,000 per ton during 2007, with the year-end closing price at $825 per ton. The total value of NOx allowances traded in 2007 exceeded $350 million.
OIG’s report is causing EPA to take a close look at the applicable programs and regulations. The Agency is currently embarking on several initiatives to improve oversight of protocol gas cylinders.
EPA regulations for major sources of air emissions require that CEMS periodically undergo calibration and accuracy tests. Calibration tests check the accuracy of CEMS by running a gas mixture of a known concentration through the systems and comparing the systems’ readings with the known concentration. The systems are adjusted accordingly to eliminate measurement inaccuracies. The certified concentrations of gaseous mixtures used to calibrate and test monitoring systems should accurately reflect the true gaseous concentration. Vendors must use an EPA protocol to ensure that the calibration gases in the protocol cylinders meet certain NIST standards.
OIG was largely motivated to investigate protocol gas cylinders by inconsistency on the part of other EPA offices in checking accuracies.
A program of annual tests run by EPA’s Office of Research and Development (ORD) was discontinued after 1997.
Testing was resumed by EPA’s Office of Atmospheric Programs (OAP) in 2003, and 11 percent of gases in 49 cylinders did not pass the test.
OAP conducted another test in 2006, but did not release the results because of concerns about the representativeness of some of the sample gases.
Also in 2003, EPA started work on a Protocol Gas Verification Program. But the program stalled because of concerns raised by a vendor, and so far, no funding has been allocated for this work. OIG’s recent testing is the largest one-time assessment of the protocol gas industry.
OIG identified 11 companies that use 18 manufacturing locations nationwide to produce protocol gases. OIG’s contractor purchased at least one set of cylinders produced from each of the 18 manufacturing locations.
Cylinders are classified as having low, medium, or high concentrations of NO, CO2, and SO2. Ambient air monitoring systems operators generally use EPA protocol gases of lower concentrations to calibrate their monitors and perform other quality assurance tests.
OIG’s report divides the purchased cylinders into those that cost over or under $380 each. All deviations from the certified concentrations occurred with the lower-cost cylinders. Twelve of the gas components’ “true” concentrations were higher than the certified concentration, and 16 were lower than the certified concentration. All gaseous components not meeting the accuracy criterion came from 7 of the 18 facilities.
Also, the gaseous components with the most exceptions were low concentration NO and SO2. All 152 gaseous components associated with cylinders costing more than $380 each met the accuracy criterion.
OIG believes the importance of calibration gases could increase as EPA considers expanding emissions trading programs. A possible rewrite of the Clean Air Interstate Rule (CAIR) could require power plants to participate in an interstate cap-and-trade program.
Also, Congress continues to consider a cap-and-trade program to control GHG emissions. Implementing a GHG emissions cap-an-trade program could greatly expand the use and importance of protocol gases if such a program included monitoring and calibration requirements similar to the Acid Rain Program.
In addition to CO2, the primary GHGs are methane, nitrous oxide, and synthetically produced fluorinated gases.
In response to OIG’s report, EPA said it would take the following actions:
- The Office of Air and Radiation (OAR) will propose a rule for public comment in 2009 to establish a largely self-supported, annual audit program for protocol gases used for the Acid Rain Program. Meanwhile, OAR says it has initiated another OAR-funded test of EPA protocol gases.
- OAR plans to implement a separate verification program to address the lower concentration protocol gases used to calibrate continuous ambient air monitors. OAR also plans to verify EPA protocol gases supplied to state, local, and tribal agencies for calibration of continuous, ambient gaseous pollutant monitors. OAR wants to launch this program by March 2010.
- ORD plans to update and publish a revised protocol to reduce the percentage of EPA protocol gases that do not attain the Acid Rain Program’s accuracy criteria. ORD wants to issue the revised protocol by October 1, 2010.
The response from industry should be to review the quality of cylinders obtained from vendors. The disadvantages of certifications that overstate concentrations are obvious.
On the other hand, having knowledge that a cylinder will underestimate emissions and continuing to use that cylinder even if it is certified is treading in a grey area of compliance.
OIG’s report on EPA’s protocol gases is available here.