EPA Surface Ozone Readings are Inflated by Mercury Vapor – The EPA has known about positive biases caused by mercury vapor since 1999

Guest essay by Forrest M. Mims III

Accurate ozone measurements are required by the Clean Air Act, for public health, many jobs and billions of dollars are at stake. Yet since 1999 the EPA has failed to acknowledge erroneous ozone measurements biased upward by mercury vapor and other interferences.

Measurement error may apply to a supposed ozone spike in San Antonio on October 3, 2016, for on that day much of Texas was blanketed by smog and mercury vapor from coal-burning power plants. San Antonio may now be subject to EPA sanctions for a violation it may not have committed.

While the EPA has long known that ozone measurements are significantly biased upward by mercury vapor, the agency has required States to use ultraviolet ozone monitors subject to mercury interference. These ozone monitors blow air between an ultraviolet (UV) lamp and a UV detector. Ozone strongly absorbs UV, so reductions in UV arriving at the detector are proportional to the ozone in the air. But mercury vapor and other contaminants in air also absorb UV, thus, artificially inflating the amount of “ozone” that is measured. The bias can range from a few parts per billion to many more.

While writing a book on environmental science last spring, I came across a 1999 EPA report that described the mercury interference problem in detail: “Laboratory Study to Explore Potential Interferences to Air Quality Monitors.” https://www3.epa.gov/ttnamti1/archive/files/ambient/criteria/reldocs/finalreport.pdf

In the conclusion:

Low levels of mercury vapor show a marked impact on all three UV photometers at both low and high humidity. The two UV photometers with the heated scrubbers were affected the most. While heated metal scrubbers helped to reduce instrument bias for some VOCs, they seemed to increase bias due to mercury vapors

This report describes how UV ozone analyzers are vulnerable to serious interference, especially from mercury vapor and also from sulfur dioxide, VOCs and water vapor. While the EPA approved this report, the agency did not require the States to use chemiluminescent ozone monitors that are unaffected by mercury and other interferences.

Last summer the National Oceanic and Atmospheric Administration (NOAA) hired me to calibrate the world standard ozone layer instrument (Dobson 83) at Hawaii’s Mauna Loa Observatory (MLO). (Dobson 83 measures the total ozone layer, not just ozone near the ground.)

While living for two months at that alpine site 11,200 feet above the Pacific, I often checked the readings made by a mercury vapor monitor and two UV ozone monitors like those used across the US. The scientist in charge told me that mercury interference with ozone measurements is well known.

Erroneous ozone measurements could mean that at least some of the cities in the eastern half of the US in violation of the Clean Air Act may actually be complying.

Moreover, automobile emissions testing, electric vehicles and some other ozone reduction strategies will not eliminate erroneous ozone readings caused by mercury. So, I asked the Office of Inspector General (OIG) for the EPA to investigate the mercury bias in ozone measurements. The OIG declined without explanation, so I sent a second request. That request was also declined.

There’s more to this story, for atmospheric mercury, which the EPA does not monitor, is far more dangerous to human health than ozone. As reported by the San Antonio Express-News (January 27, 2011):

“Children exposed to low-dose levels of mercury in-utero can have impaired brain functions, including verbal, attention, motor control, and language deficits, and lower IQs.”

Mercury also contaminates fish in lakes and oceans. The Express-News and many other publications have reported that coal burning power plants in Texas emit more mercury than any other State. Among the main mercury emitters in Texas is CPS Energy’s Calaveras Power Station, which is located on the southeast side of San Antonio from where the wind predominantly blows.

It’s time for the EPA to cease punishing States for putative ozone “violations” caused by mercury vapor and to require a transition to ozone monitors unaffected by interferences. It’s also time for the EPA to recognize that mercury is a far more serious threat to the health of our children than ozone. Finally, it’s time for the EPA Inspector General to follow its charter and fully investigate reports about potentially serious errors in EPA ozone measurements.

Forrest M. Mims III received a Rolex Award for his ozone research, was named one of the “50 Best Brains in Science” by Discover Magazine. More at http://www.forrestmims.org/

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