The Cost of Inaccurate CEM Calibration Gases

Utility companies and other users of Continuous Emissions Monitoring (CEM) calibration gases often mistakenly consider them a commodity, making price the primary purchase consideration. Consequently, many are willing to settle for calibration gases that are less accurate than premium calibration gases, as long as they are also less expensive.

But many companies are beginning to see that buying less expensive and potentially inaccurate CEM calibration gases may, ironically, lead to losing hundreds of thousands or millions of dollars! This is because the use of inaccurate calibration gases often leads to the overstatement of emissions that could otherwise be claimed as valuable emission credits which are trading at values ranging from $700 to $2,500 per ton.

For instance, if a company uses a calibration gas mixture that has been inaccurately manufactured and certified with a 100 ppm tag value, but in reality contains only 96 ppm, that company would unwittingly calibrate its CEM incorrectly, and overstate its emission levels. Noting the image below, this inaccurate calibration gas would eventually lead to tons of lost emission credits that could have been sold, banked for future use, or traded for significant dollars. Now, they are lost forever.

Accurate CEM calibration gases not only allow companies to comply with EPA standards, but ultimately save significant amounts of money in emission credits that might otherwise be lost.

Failing to Measure Up

EPA regulations, as stated in the Clean Air Act of 1990, require that protocol gases used to calibrate CEMs for Nitric Oxide or Sulfur Dioxide (SO2) emissions be within ±2% of the accuracy value as stated by the manufacturer on the mixture's certificate of analysis, or 'tag' to comply with the EPA mandated 7 - Day Drift test. However, in a recent EPA blind audit, in which three cylinders of calibration gases were bought from fourteen different specialty gas manufacturers, it was found that 43% of the vendors (6 of 14) failed to comply with the ±2% accuracy requirement. The inaccuracies, in fact, ranged from 2% to as high as 8%.

If the CEM error rate due to calibration is, between 2% and 8%, then America's acid rain utilities could be overstating emissions by 82,050 to 328,203 tons of SO2 each year.  With the SO2 current market value at $700 per ton, this results in $57,435,000 to $229,742,100 lost potential emission credits this year - with the utility companies that use unacceptably inaccurate calibration gases, such as those produced by the 43% of vendors who failed the blind audit, bearing much of that loss.

The Cost of Inaccuracy
In order to fully understand the significance of these numbers, imagine a utility company with a total SO2 Allowance Trading System (ATS) credit of 400,000 tons for one year, but which also used calibration gases that were actually 2% higher than the tag value.  That company would likely be overstating emissions by 8,000 tons (400,000 tons x 2%), which, at a value of $700/ton, means it would be losing over $5 million in allowance credits which could have been banked or sold that year.  Companies using calibration gases bought from vendors who failed the blind audit, and whose gases therefore exceed the 2% accuracy requirement, stand to lose even more.

Such a gross loss of potential trading credits clearly overshadows the higher initial cost of accurate CEM calibration gases.  This year's blind audit reveals the scope of the problem of inaccurate gases, and utility companies would do well to take notice.  The companies could not see the difference because they calibrated their CEMs based on the tag values of these calibration gases.   This problem is one which is only detectable after an annual or semi annual Relative Accuracy Test Audit (RATA)  as mandated by EPA.

Bob Davis is the Environmental Marketing Manager with Scott Specialty Gases, the world's largest producer of EPA Protocol gases and a leading global manufacturer of specialty gases for all types of applocations. More information on the company and Scott's products can be found at .

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