Interagency Comparison of lodometric Methods for Ozone Determination

Abstract

In 1973 it was learned that measurements of oxidants by the Los Angeles Air Pollution Control District (LAAPCD) were about 30 percent lower than measurements by the California Air Resources Board (ARB) and that the discrepancy was due to differences in the calibration methods of the two agencies. To resolve this problem, the ARB appointed an Oxidant Calibration Committee for the purpose of evaluating the accuracy of the different agency calibration procedures. The committee selected ultraviolet absorption photometry as the reference method for ozone measurement. Interagency comparisons of the various iodometric methods were conducted relative to the ultraviolet standard. The tests included versions of the iodometric methods as employed by ARB, LAAPCD, and the Environmental Protection Agency (EPA). An alternative candidate reference method for ozone measurement, gas phase titration, was also included in the test series. Under the conditions of these tests, which were considered to be representative of procedures employed by the California agencies, the ARB method read high by 25 to 30 percent, and the LAAPCD method read low by about 4 percent. The EPA method, which is similar to the ARB method, also read high. The gas phase titration results were about 9 percent higher than the reference ultraviolet standard. Based on the results of these tests and other considerations, the committee has recommended that future ozone calibration procedures in the State of California be referenced to an ultraviolet standard.

Ambient air measurements of hydrogen peroxide in the California South Coast Air Basin

“…In contrast, on July 25 and 26,1977, ozone concentrations reached approximately 0.3 ppm in Riverside, but H2O2 concentrations observed with the chemiluminescent method were between 25 and 30 ppb; whereas on July 28, O3 peaked at approximately 0.2 ppm, but H2O2 concentrations were less than 20 ppb as measured by all three methods. These differences in concentrations of H2O2, relative to O3 or oxidant, between the 1970 and 1977 studies are probably actually greater than indicated by the raw data cited, since in the earlier study oxidant rather than ozone was measured, and in the time between the two studies the calibration procedure in the Federal reference method for oxidant has been shown to result in oxidant measurements approximately 10-20% too high (16,17). Whether or not the apparent decline in ambient H2O2 concentrations between 1970 and 1977 is real is difficult, if not impossible, to establish.…”

“…Atmospheric H2O2 can be sampled by trapping the H2O2 in a midget impinger and analyzing the solution directly. In the present study sampling intervals were [15][16][17][18][19][20] min, and this gave a detection limit of approximately 0.4 ppb for gas phase H2O2.…”

PAN and oxidant measurement in ambient atmospheres

“…The EPA-CAMP station in St. Louis used neutral buffered KI for oxidant determinations, whereas the Los Angeles APCD employs neutral unbuffered KI. Recent studies have shown as much as 40% differences between these two KI solutions (25)(26)(27). These differences are important if one chooses to compare Ox/ PAN ratios between cities; however, these types of comparison were not made in this paper.…”

Effects of Peroxyacetyl Nitrate Alone and in Combination with Ozone in Healthy Young Women

“…to 0.55 ppm and 0.90 ppm) to account for the difference between the ultraviolet photometry O3 standard of the present study compared to the potassium iodide O3 standard in use when the prediction equations were developed. 16 Although the use of prediction equations on subjects other than those on whom the equations were developed introduces uncertainties into the resulting predictions, we used the equations to obtain an estimate of the size of any additional decrement in pulmonary that might be expected if the difference in the response to 0.27 ppm PAN + 0.48 ppm O3 compared to 0.48 ppm O3 was similar to the difference in response predicted for exposure to 0.75 ppm O3 compared to exposure to 0.48 ppm 63. …”