tion by the coulometric method would be an unrealistic 0.018 PPm. On April 27,1977, a year before publication in ES&T, the paper by Fein and Bailey was presented a t a public hearing held by the California Air Resources Board in Los Angeles to reconsider the California air quality standard for sulfur dioxide. I submitted the four comments above to the public hearing record in June 1977. Apparently my comments did not get to the authors. The first and second comments can be verified by calling the air pollution control districts that provided the data. Validation of the fourth comment is a matter of simple arithmetic. The negative bias of the data due to thermal instability problems of the pararosaniline reagent was announced in December 1975 by John B. Clements of the EPA ( 1 ) .An estimate of the extent of the bias was presented in a draft by the Standing Air Monitoring Workgroup of the EPA ( 2 ) .According to the report, data obtained a t air monitoring sites by the pararosaniline method could be low by as much as a factor of two. If samples were allowed to sit several days a t elevated temperatures for several days, the data could be low by more than a factor of two. It is clear that, except when obtained under controlled temperature conditions, SO2 data by the pararosaniline mlethod are unreliable and should not be used to assess bias or precision of other air monitoring methods. Literature Cited (1) Clements, J. El., Chief Quality Assurance Branch, EMSL, U.S. EPA, memorandum on “Problems with the Federal Reference Method” for SO2 to Regional EPA Administrators dated Dec 29, 1975. (2) Environmental Protection Agency, Standing Air Monitoring Workgroup, Draft Report “Strategies for Improved SO1 Monitoring, August 1976”.
John R. Kinosian Technical Services Division Air Resources Board 1102 Q Street Sacramento, Calif. 95812
SIR: In regard to Dr. John R. Kinosian’s letter of August 22, it is unfortunate that he only now calls our attention to the misidentification of three of the four data sets used in our note. However, as shown below, reanalysis of the data using appropriate data set groupings confirms the magnitude of the random and bias errors of the conductimetric (California reference) method and shows that the coulometric (California equivalent) method has the same errors. Thus, the coulometric as well as the conductimetric methods are unsuitable for setting and determining compliance with low SOL standards. Our response to the specific points raised by Kinosian follows: The data in the NADB can usefully serve as a source of air quality inforrnation only if it is correct. Inquiries have revealed that the California Air Resources Board has not taken any action to correct the method misidentifications in their NADB submissions, even though they have been aware of the problem for more than a year. Accepting that the continuous SO2 data from Anaheim, San Bernardino, and San Diego were obtained by the California equivalent coulometric method, a reanalysis using appropriate data set groupings yields the results shown in Table I. The random errors for both continuous methods are essentially the same a t the f0.020 ppm ( f 3 6 ) previously found for the four-site composite. Similarly, the random errors for the pararosaniline method in both site groupings remain essentially a t the previously found f0.006 ppm. Also, estimated
Table 1. Reanalysis Summary bias, ppm
site groups
random error, ppm pararoscontlnuous aniline variavarlamethod billty biilty
Los Angeles
cond. Anaheim, coul. San Bernardino, and San Diego
max obsd
f0.020 f0.007
0.040
f0.019
0.029
f0.006
ppm by conlinuous method
0.027 0.033
(mean)
relative bias for the two groups is close to the previous 0.030 ppm mean of the four-site composite. Obviously, neither the conductimetric nor the coulometric methods can acceptably be used to set or determine compliance with a 0.04- or 0.05-ppm standard. This agrees with Stevens et al. ( 1 ) and confirms our previous conclusions on the conductimetric method. We were aware of the positive data handling bias in the Los Angeles data resulting from reporting all measurements below 0.01 ppm as 0.01 ppm. We included these system-biased data because such data are being used to justify further control of sulfur oxide emissions ( 2 ) . Kinosian implies that the bias between the methods is largely attributable to the pararosaniline method, which can yield erroneously low values when precautions are not observed in warm weather use. If this is the source of the bias, the smallest relative biases would be expected in the coldest months when the thermal effects are at a minimum. This did not occur and, in fact, the data for the winter months show a slightly greater than proportional share of the highest biases. Further, the variability data in Table I11 of our note show smaller variability for the pararosaniline method measurements than for the continuous methods; this would not be expected if pararosaniline errors were seasonally related and dominated the relative bias. Kinosian implies that the extrapolation of relative bias to 0.04 ppm by the coulometric method a t San Bernardino is in error. This extrapolation is valid because it is heavily weighted by data which are above the coulometric method detection limit and extend up to 0.032-ppm 24-h average concentration. As Kinosian and our note point out, the similar extrapolation to 0.04 ppm by the pararosaniline method is not meaningful. In total, Kinosian’s comments emphasize the main point of our note-S02 measurements by the California reference and equivalent methods have systematic and random errors that are large compared to the California air quality standards. Because air monitoring data are the basis for setting standards, determining compliance, establishing control strategies, and granting of permits, use of these methods will introduce errors into the regulatory process and will adversely affect the economic, energy, and environmental well-being of millions of people. With such important socioeconomic impacts a t stake, it is imperative that control agencies use only the most accurate and precise monitoring methods and always act to reduce the magnitude and the effects of the data errors.
00 13-936X/79/0913-0483$01 .OO/O @ 1979 American Chemical Society
Literature Cited (1) Stevens. R. K., Hodgeson, J . A,, Rallard, I,. F., Decker, C. E., in “Determination of Air Quality“, Mamantov, G.. and Shults, LV. D., Eds., pp 83-108, Plenum, New York. 1972. ( 2 ) Damesworth, W., et al., “Sulfur Dioxide/Sulfate Control Study“, South Coast Air Quality Management District, April 1978.
Richard S. Fein Bruce S. Bailey Texaco Research Center Beacon, N.Y. 12508
Volume 13, Number 4, April 1979 483
