the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 15 Jun 2023
Obtaining the true NMHC data for ambient air in urban: comparison of NMHC data between indirect and direct methods
Song Gao
Yong Yang
Xiao Tong
Linyuan Zhang
Yusen Duan
Guigang Tang
Qiang Wang
Changqing Lin
Qingyan Fu
Lipeng Liu
Lingning Meng
Abstract. Since non-methane hydrocarbons (NMHCs) include numerous species of volatile organic compounds (VOCs), they are the only indicators that can characterize the total amount of VOCs in ambient air. More than 90 % of NMHC instruments in the market use the indirect method for NMHC determination, utilizing a gas chromatograph to determine the concentrations of total hydrocarbons (THCs) and methane in air. However, we found indirect NMHC measurements incorrectly characterized the low NMHC concentrations in the urban air. These measurements were hindered by the uncertain changes in the errors associated with low THC concentrations, humidity, and macroscopic substances (oxygen) in the atmosphere. In this study, we conducted intercomparisons between 10 instruments in the market using different operation principles; among these, two used the direct method and eight used the indirect method. For the indirect method, experiments showed that when the NMHC concentration was 50 ppbC, the errors in the measurement results were 32 % (CH4) and 98 % (THC) when compared to theoretical values. The oxygen content in the sample gas directly affected the response of the THC. The effect of increased oxygen content on the analysis of oxygen-containing substances was more significant than that of the increase in hydrocarbon substances. The response of dry zero was blank, and the response value increased non-linearly with relative humidity (RH). RH had a great impact on low NMHC concentrations of nearly 50 %. For the direct method, although various flow designs were applied for different instruments, the results indicated that they generally showed lower interference and higher accuracy for the ambient NMHC measurements. With the online direct methods, we obtained more reliable data and characteristics for low-concentration NMHCs in downtown Shanghai. The median of hourly data was 163.1 ppbC, and the highest ratio of the maximum and minimum concentrations of NMHCs reached 9.56 in a single day.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1299 KB) - Metadata XML
- BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Song Gao et al.
Interactive discussion
Status: closed
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CC1: 'Comment on egusphere-2023-293', shuang fu, 31 Jul 2023
some questions on this study：(1) What are the main errors in indirect measurement of NMHCs?
(2) How is the measurement result improved after the method adjustment of the NMHC instrument?
Citation: https://doi.org/10.5194/egusphere-2023-293-CC1 -
AC1: 'Reply on CC1', Song Gao, 16 Aug 2023
(1) What are the main errors in indirect measurement of NMHCs?
Response:
We appreciate your questions. We found indirect NMHC measurements incorrectly characterized the low NMHC concentrations in the urban air. These measurements were hindered by the uncertain changes in the errors associated with low THC concentrations, humidity, and macroscopic substances (oxygen) in the atmosphere.
(2) How is the measurement result improved after the method adjustment of the NMHC instrument?
Response:
We appreciate your questions.The error from accurate values is reduced.The average daily NMHC concentration was 162.6 ppbC, and daily NMHC values ranged from 83.8 to 309.9 ppbC. The hourly NMHCs over 300 ppbC only occurred 56 times in a total of 1035 results; meanwhile, lowest and highest NMHC values reached 42.8 and 562.3 ppbC, respectively. The majority of values ranged from 60 to 300 ppbC when the AQI was excellent. Through lab tests and field observations, we found that the results of all the indicators of instruments using the direct method were better than those using the subtraction method and the instruments using the direct method could obtain scientific data.Â
Citation: https://doi.org/10.5194/egusphere-2023-293-AC1
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AC1: 'Reply on CC1', Song Gao, 16 Aug 2023
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RC1: 'Comment on egusphere-2023-293', Anonymous Referee #1, 14 Aug 2023
I thoroughly reviewed this manuscript. A lot of online monitoring NMHC instruments were tested, and the main problems in the experimental results were carefully analyzed by mainly focusing on the low concentration error, oxygen interference, humidity impact, and response factor. Low concentration error and humidity affected the accuracy of the results, and the response factor could sometimes not meet the theoretical value. This study optimized and conducted an experimental program for the online monitoring of the NMHC instrument using the direct method. Moreover, changing the enrichment and specially designed columns further improved the test effect.
I have listed some specific comments (see below) for this paper, and it is recommended to make minor modifications before publication.
1.Please further clarify the definition of NMHC.
2.Please make sure your ‘conclusion’ section underscore the scientific value added of your paper, and/or the applicability of your findings/results, as indicated previously.
3.The language of the paper needs careful editing and professional proofreading. Further, the entire manuscript should be written in the third person plural or singular perspective. Please avoid the use of "we" or "our".Citation: https://doi.org/10.5194/egusphere-2023-293-RC1 -
AC2: 'Reply on RC1', Song Gao, 16 Aug 2023
1.Please further clarify the definition of NMHC.
Response:
We appreciate your question.the definition of NMHC is Non-Methane Total Hydrocarbons.
2.Please make sure your ‘conclusion’ section underscore the scientific value added of your paper, and/or the applicability of your findings/results, as indicated previously.
Response:
We appreciate your question.The conclusion and applicability of findings/results in our manuscript meet the requirements.
3.The language of the paper needs careful editing and professional proofreading. Further, the entire manuscript should be written in the third person plural or singular perspective. Please avoid the use of "we" or "our".
Response:
We appreciate your question.In our manuscript, we have paid attention to this point.
Citation: https://doi.org/10.5194/egusphere-2023-293-AC2
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AC2: 'Reply on RC1', Song Gao, 16 Aug 2023
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RC2: 'Comment on egusphere-2023-293', Anonymous Referee #2, 15 Aug 2023
I agree the  the manuscript should be accepted as is.
Citation: https://doi.org/10.5194/egusphere-2023-293-RC2 -
AC3: 'Reply on RC2', Song Gao, 16 Aug 2023
I agree the  the manuscript should be accepted as is.
Response:
We thank you for your recognition of our manuscript.
Citation: https://doi.org/10.5194/egusphere-2023-293-AC3
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AC3: 'Reply on RC2', Song Gao, 16 Aug 2023
Interactive discussion
Status: closed
-
CC1: 'Comment on egusphere-2023-293', shuang fu, 31 Jul 2023
some questions on this study：(1) What are the main errors in indirect measurement of NMHCs?
(2) How is the measurement result improved after the method adjustment of the NMHC instrument?
Citation: https://doi.org/10.5194/egusphere-2023-293-CC1 -
AC1: 'Reply on CC1', Song Gao, 16 Aug 2023
(1) What are the main errors in indirect measurement of NMHCs?
Response:
We appreciate your questions. We found indirect NMHC measurements incorrectly characterized the low NMHC concentrations in the urban air. These measurements were hindered by the uncertain changes in the errors associated with low THC concentrations, humidity, and macroscopic substances (oxygen) in the atmosphere.
(2) How is the measurement result improved after the method adjustment of the NMHC instrument?
Response:
We appreciate your questions.The error from accurate values is reduced.The average daily NMHC concentration was 162.6 ppbC, and daily NMHC values ranged from 83.8 to 309.9 ppbC. The hourly NMHCs over 300 ppbC only occurred 56 times in a total of 1035 results; meanwhile, lowest and highest NMHC values reached 42.8 and 562.3 ppbC, respectively. The majority of values ranged from 60 to 300 ppbC when the AQI was excellent. Through lab tests and field observations, we found that the results of all the indicators of instruments using the direct method were better than those using the subtraction method and the instruments using the direct method could obtain scientific data.Â
Citation: https://doi.org/10.5194/egusphere-2023-293-AC1
-
AC1: 'Reply on CC1', Song Gao, 16 Aug 2023
-
RC1: 'Comment on egusphere-2023-293', Anonymous Referee #1, 14 Aug 2023
I thoroughly reviewed this manuscript. A lot of online monitoring NMHC instruments were tested, and the main problems in the experimental results were carefully analyzed by mainly focusing on the low concentration error, oxygen interference, humidity impact, and response factor. Low concentration error and humidity affected the accuracy of the results, and the response factor could sometimes not meet the theoretical value. This study optimized and conducted an experimental program for the online monitoring of the NMHC instrument using the direct method. Moreover, changing the enrichment and specially designed columns further improved the test effect.
I have listed some specific comments (see below) for this paper, and it is recommended to make minor modifications before publication.
1.Please further clarify the definition of NMHC.
2.Please make sure your ‘conclusion’ section underscore the scientific value added of your paper, and/or the applicability of your findings/results, as indicated previously.
3.The language of the paper needs careful editing and professional proofreading. Further, the entire manuscript should be written in the third person plural or singular perspective. Please avoid the use of "we" or "our".Citation: https://doi.org/10.5194/egusphere-2023-293-RC1 -
AC2: 'Reply on RC1', Song Gao, 16 Aug 2023
1.Please further clarify the definition of NMHC.
Response:
We appreciate your question.the definition of NMHC is Non-Methane Total Hydrocarbons.
2.Please make sure your ‘conclusion’ section underscore the scientific value added of your paper, and/or the applicability of your findings/results, as indicated previously.
Response:
We appreciate your question.The conclusion and applicability of findings/results in our manuscript meet the requirements.
3.The language of the paper needs careful editing and professional proofreading. Further, the entire manuscript should be written in the third person plural or singular perspective. Please avoid the use of "we" or "our".
Response:
We appreciate your question.In our manuscript, we have paid attention to this point.
Citation: https://doi.org/10.5194/egusphere-2023-293-AC2
-
AC2: 'Reply on RC1', Song Gao, 16 Aug 2023
-
RC2: 'Comment on egusphere-2023-293', Anonymous Referee #2, 15 Aug 2023
I agree the  the manuscript should be accepted as is.
Citation: https://doi.org/10.5194/egusphere-2023-293-RC2 -
AC3: 'Reply on RC2', Song Gao, 16 Aug 2023
I agree the  the manuscript should be accepted as is.
Response:
We thank you for your recognition of our manuscript.
Citation: https://doi.org/10.5194/egusphere-2023-293-AC3
-
AC3: 'Reply on RC2', Song Gao, 16 Aug 2023
Peer review completion
Journal article(s) based on this preprint
Song Gao et al.
Song Gao et al.
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1299 KB) - Metadata XML