CORRESPONDENCE
SIR: Lonneman has concluded that the moisture anomaly in the analysis of peroxyacetyl nitrate reported by Holdren and Rasmussen ( I ) was unique to their system. In response to the claim that our observations were unique, we reference several other investigators’ comments upon this effect. Nieboer and Van Ham (2) have recently reported that “the elution gas stream was previously humidified by passing it over Na2S203‘5H20 (analytical grade Merck), because it appeared that the height of the PAN peak depends on the relative humidity of ambient air if dry elution gas was used”. This article appeared in the literature a t the same time as our original article and thus could not be included in our list of references. Stephens and Price (3) stated that “the diluent should be air of normal humidity so that the chromatogram will be a realistic one”. Although there was no further explanation given, it appeared that this author too had experienced some moisture difficulty when analyzing for PAN. Penkett and Sandalls, in correspondence ( 4 ) with our laboratory, indicate their data show an increased response to PAN analyses by pretreating the column substrate with acetone. The authors suggested that the acetone treatment temporarily reduced the active sites present on the column and that PAN analyses were substrate sensitive. We feel that there is a definite problem in analyzing for PAN under varying humidity conditions. Why or how it happens is uncertain. We definitely believe it is not unique to our laboratory, and investigators reporting PAN measurements should be aware of this fact. Literature Cited (1) Holdren, M. W., Rasmussen, R. A., Environ. Sei. Technol., 10,
185 (1976). (2) Nieboer, H., Van Ham, J., Atmos. Enuiron., 10,115 (1975). (3) Stephens, E. R., Price, M. A.,J. Chem. Educ., 50,351 (1973). (4) Penkett, S. A., Sandzlls, F. J., private communication.
Michael W. Holdren Reinhold A. Rasmussen Atmospheric Resources Section College of Engineering Washington State University Pullman, Wash. 99163
196
Environmental Science & Technology
SIR: When my original manuscript was submitted to ES&T, the Holdren and Rasmussen ( I ) article was the only report I was aware of that suggested a water effect on the response of PAN in a gas chromatograph-electron capture system. Therefore, the use of the term “unique” seemed to be appropriate. The article by Nieboer and Van Ham (2),which reported a water vapor effect on the peak height of the PAN peak, did not come to my attention until sometime later and was not referenced in my manuscript. In their report ( 2 ) , however, the authors did not go into the details of this interference. Also, it is not clear from their description the magnitude of this effect. One could conclude from their report that variation in the water vapor content may have affected the geometry of the eluding PAN peak but did not necessarily affect the peak area response of PAN. Stephens and coworkers have published several articles pertaining to the measurement of PAN in ambient atmospheres without the suggestion of a water interference. The statement made by Stephens and Price in the 1973publication ( 3 )that “the diluent should be air of normal humidity so that the chromatogram will be a realistic one” can be interpreted in many ways. Since this comment was not expanded upon, one could conclude that the authors intended this as an instructive statement and were not referring to any water anomaly problems. The purpose of my manuscript was to present PAN and water data a t similar concentrations and relative humidities as those reported by Holdren and Rasmussen and to show that these were free of water anomaly effect. I also included a brief outline of past experiences and difficulties in the construction of a suitable GC system for PAN. These difficulties are apparently shared by other experimenters who have attempted this analysis. The purpose of my manuscript was not to discredit the work of Holdren and Rasmussen, but to point out that their results are not necessarily observed in all GC systems for PAN analysis. Literature Cited (1) Holdren, M. W., Rasmussen, R. A., Enuiron. Sei. Technol., 10, 185 (1976). (2) Nieboer, H., Van Ham, J., Atrnos. Enuiron. 10, 115 (1976). (3) Stephens, E. R., Price, M. A., J. Chern. Educ., 50,351 (1973).
William A. Lonneman U S . Environmental Protection Agency National Environmental Research Center Research Triangle Park, N.C. 2771 1
