Water vapor inhibits hydrogen sulfide detection in pulsed fluorescence sulfur monitors

. The Thermo Scientiﬁc 450 Hydrogen Sulﬁde– Sulfur Dioxide Analyzer measures both hydrogen sulﬁde (H 2 S) and sulfur dioxide (SO 2 ). Sulfur dioxide is measured by pulsed ﬂuorescence, while H 2 S is converted to SO 2 with a molybdenum catalyst prior to detection. The 450 is widely used to measure ambient concentrations, e.g., for emissions monitoring and pollution control. An air stream with a constant H 2 S concentration was generated and the output of the analyzer recorded as a function of relative humidity (RH). The analyzer underreported H 2 S as soon as the relative humidity was increased. The fraction of undetected H 2 S increased from 8.3 at 5.3 % RH (294 K) to over 34 % at RH > 80 %. Hydrogen sulﬁde mole fractions of 573, 1142, and 5145 ppb were tested. The ﬁndings indicate that previ-ous results obtained with instruments using similar catalysts


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Printer-friendly version Discussion paper them and the relevant supporting data.
Author Response: The authors would like to thank the reviewer for the positive evaluation.
There are many alternative drying techniques available; however this study has only tested the Nafion dryer.The authors found that there was no interference between the Nafion tube and the measured H2S or SO2 concentrations and can therefore verify the Nafion dryer as a viable technique.Since no other techniques were tested in the present study, the authors cannot currently verify any alternative drying techniques.

_____ Anonymous Referee #2
Received and published: 11 April 2016 General comments: This paper reported an interesting and important issue of H2S measurement using the pulsed fluorescence technology.The findings of the paper reveal a possible under-estimation of true H2S concentrations in some previous research using this type of H2S analyzers.However, the paper should be improved and a careful check to correct some errors in it is necessary.
Author Response: The authors thank the reviewer for their comments and address further questions below.Title: The word "inhibit" appears in the paper more as "interfere".It is not consistent as what is described in the research.
Author Response: Several suggestions for the title were discussed including "interfere" as an alternative to "inhibit".However, the authors agreed that the word "inhibit" better fits the observations, since the H2S response of the instruments is inhibited by water vapor.
Line 2 and throughout the manuscript: Normally, a sentence should not be started with

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Printer-friendly version Discussion paper an abbreviation or a chemical formula.
Author Response: Changes have been made throughout the paper to avoid starting sentences with abbreviations and chemical formula.
Line 4 and throughout the manuscript: The "e.g." should usually followed by a "," as in "e.g.,".
Author Response: The comma has been added after each e.g..mixturebefore continuing.Part of the diluted H2S stream was lead through a Perma Pure "Nafion dryer" by the 450, while the rest was "bled" into a "fume hood", avoiding overpressure on the sampling line.The "Nafion dryer" was used to humidify the "dry test gas", by allowing water to permeate the Nafion membrane from a "humid purge gas".
Author Response: The verbs in the text and some of the labels in the Figure have been altered to better fit each other.This should make it easier to follow the description given in the text when referring to the Figure.
Line 23: A more representative publication for the National Air Emissions Monitoring Study is: Heber, A.J., B.W. Bogan, J.-Q.Ni, T.-T.Lim, E.L. Cortus, J.C. RamirezDorronsoro, C.A. Diehl, S.M. Hanni, C. Xiao, K.D. Casey, C.A. Gooch, L.D. Jacobson, J.A. Koziel, F.M. Mitloehner, P.M. Ndegwa, W.P. Robarge, L. Wang, and R. Zhang.2008.The National Air Emissions Monitoring Study: overview of barn sources.In: The Eighth International Livestock Environment Symposium (ILES VIII).Iguassu Falls, Brazil, September 1-5: St. Joseph, Mich.: ASABE.Author Response: The more representative publication is now used instead of the earlier reference.Line 25: "proposed by" should be "approved by".Author Response: This has been corrected Line 65: Explain about "technical air".". ..a 100 ppm H2S bottle"; in Table 1, it is 101 ppm.Author Response: A description of technical air has been added to introduce the term technical air.Furthermore "a 100 ppm H2S bottle " has been corrected to "a 101 ppm H2S bottle" as stated in the Table -The flask was purchased as a 100 ppm H2S flask with the actual content determined to be 101 ppm by the manufacturer.Lines 66 to 70: Make the names and verbs in the text the same as used in the Figure.It is difficult to follow your description as it is now when referring the figure. . .