Ozone Results
Creighton University
Part 6.
EPA method, "Determination of Ozone by Ultraviolet Analysis"

Results of 3/4 December 2002

The following results were obtained by Scot Eskestrand on 3 and 4 December 2002.  We used the newest EPA method, "Determination of Ozone by Ultraviolet Analysis"  This method can be downloaded as a pdf file.  In Section 9.1.1 of the method, the extinction coefficient for gas phase ozone is given as 308.8 atm-1 cm-1 at 273 K and 1 atm.  Scot and I set up the apparatus as shown here using an Agilent 8453 UV-spectophotometer.

The flow of gas mixture (2/3 of which is H2 and 1/3 is O2 with trace amounts of O3) was delivered to an upside down silica cuvette in the sample chamber as shown here.  The delivery tube was threaded to the top of the cuvette.

After running the "Blank" with air in the cell, the ozone generator was turned on.  We fanned fresh air into the sample chamber so that the concentration of ozone outside of the cell, but in the beam's light-path, would be ozone-free.  We recorded a variety of spectra (24 in all!) over a 10 minute period with a maximum absorbance of 0.37.

Using the EPA's extinction coefficient, we can solve for concentration of ozone:

A = a . b . c

0.37 = (308.8 atm-1 cm-1)(1 cm) . c

c = 0.0012 atm

Given the atmospheric pressure was 0.98 atm, the percent ozone in the mixture was:

percent ozone = 100% X 0.0012 atm / 0.98 atm
= 0.12 %