Instruments

Surface Ozone measurements are made by Thermo Scientific Model 49 C and I or TwoBTechnologies Model 205 ozone monitors. These instruments are dual cell UV photometers which function on the absorption of UV light by ozone at 254nm and relating the UV absorption to the ozone concentration following the Beer-Lambert law. Sample air is pulled through a particle filter and into the instrument cells. Sample air enters one detection cell and “zero air” (charcoal scrubber removes all ozone in the sample) enters through the other cell. The ozone concentration is calculated from the UV light intensities detected from the two cells comparing the difference in the two cells. The instrument alternates the two cells to ensure that there is not a bias in one of the detection cells. The data is continuously collected at one minute intervals and averaged to one hour values for research and reporting to open data centers. The instruments are routinely calibrated to the NIST-traceable standard held at the NOAA David Skaggs Research Center in Boulder, Colorado.