From Sacramento to Stockholm, Accurate Ozone Measurements Depend on NIST

Everyone wants to measure ozone, or so it seems.  Scientists are continually monitoring the ozone hole in the upper atmosphere.  Weather reports often caution city dwellers about high ozone levels on hot summer days.

With so many people around the world measuring ozone, how do we know which measurements are accurate?  When scientists in Europe and the United States conduct separate studies of the ozone hole, does it make sense to compare their results?

Yes, say researchers at the National Institute of Standards and Technology who with the Environmental Protection Agency have created an ozone monitoring network that covers the United States, Canada and Europe.  The network includes 15  standard reference photometers, instruments for calibrating ozone measuring devices.

The network recently has expanded to include the Federal Office of Metrology in Bern, Switzerland, and will expand further to include the Swiss Federal Laboratories for Materials Testing and Research in Dubendorf, Switzerland, in September.

"We completed the first two standard reference photometers in 1983, and as the need for accurate ozone measurements has grown, so has our program," says James Norris, the NIST electronics technician who built most of the instruments in the
network.  "We've worked with the EPA to design an instrument that is as accurate as technologically possible."

The standard reference photometers measure the concentration of ozone in an air sample with an uncertainty believed to be no more than 1 percent.  The instruments are used to calibrate ozone measuring devices in the countries and states in which they are located.  This allows environmental agencies worldwide to make accurate comparisons of ozone measurements.

Atmospheric scientists have been measuring ozone losses in the upper atmosphere since the early 1970s.  Ozone losses allow more ultraviolet light to penetrate the atmosphere with potential harm to human health, agriculture and marine life.

On the other hand, ground-level ozone is an irritant to the lungs and eyes.  It can weaken rubber, fade colors and damage plant life.  As ground-level ozone reacts in the lower atmosphere, it contributes to smog in both rural and urban areas.

In light of these health and environmental concerns, the EPA and NIST (then known as the National Bureau of Standards) designed and built the first two standard reference photometers. One now serves as the EPA ozone standard in Raleigh, N.C., and the other is the NIST ozone standard.

In the joint NIST-EPA program, standard reference photometers were placed in Raleigh, N.C., Edison, N.J., Sacramento, Calif., Houston, Chicago, Denver, Boston, Atlanta and Kansas City, Mo.

The network of standard reference photometers also includes one at the Institute of Applied Environmental Research at the University of Stockholm, Sweden, which is used to calibrate instruments in more than 20 other countries in Europe's Tropospheric Ozone Research Program, and one at the Ontario Ministry of Environment in Toronto.  The Federal Office of Metrology in Bern, Switzerland, received the latest instrument in June.  

A standard reference photometer is small enough to fit on a desktop and measures ozone generated by an ultraviolet lamp inside the unit or from an external source.  In addition to building standard reference photometers, NIST calibrates ozone measuring devices for industry and other government agencies.

NIST is the only federal technology agency with the primary mission of helping U.S. industry to strengthen its competitiveness.  Through research, services, grants and outreach programs, NIST assists industry in developing, adapting and commercializing technologies that lead to greater productivity, higher quality, and new and improved products and services.  NIST is an agency of the U.S. Commerce Department's Technology Administration.