Ground-based Measurements of Atmospheric Trace Gases in Beijing during the Olympic Games
|Reviewer 1 Heshun Wang Center for Satellite Applications and Research (STAR), NOAA||Reviewer 2 Luke Surl LPC2E & LATMOS, CNRS|
Approved with revisions
Approved with revisions
|Version 2||Reviewer invited||Reviewer invited|
Published: 5 December 2018
AbstractA portable Fourier Transform Spectrometer (B3M-IR) is built and used to measure atmospheric trace gases in the city of Beijing during Olympic Games in 2008. A short description of the instrument is first provided in this paper. A detailed spectral analysis is then presented. The total columns of ozone (O3), carbon monoxide (CO), methane (CH4) and nitrous oxide (N2O) are retrieved from the ground-based solar absorption spectra recorded by the B3M-IR during the Olympic Games. Lacking validation data, only the retrieved total column of O3 is compared with that retrieved by MAX-DOAS, which is deployed at the same station. The mean difference between the two methods of measurement is 6.5%, demonstrating the performance and reliability of B3M-IR.
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Cheng, J. Ground-based Measurements of Atmospheric Trace Gases in Beijing during the Olympic Games. Sci 2019, 1, 6.
Cheng J. Ground-based Measurements of Atmospheric Trace Gases in Beijing during the Olympic Games. Sci. 2019; 1(1):6.Chicago/Turabian Style
Cheng, Jie. 2019. "Ground-based Measurements of Atmospheric Trace Gases in Beijing during the Olympic Games." Sci 1, no. 1: 6.
Center for Satellite Applications and Research (STAR), NOAA
It’s an interesting topic to investigate the trace gases using a new ground based FTIR, the validation is preliminary, but the trend is impressive during such a well-known event. Some minor suggestions:
1. The author should provide more details about the key part of the research even for a letter.
(1) The FTIR observations, does it just perform the measurements at 13:30PM under clear-sky condition? More details should be added.
(2) How do you combine the four datasets of priori VMR profiles?
(3) More description about the fundamental theoretical basis about the SFIT2 algorithm. What’s the input and output of SFIT2? You just use the selected micro-window
(4) More details about the evaluation reference data, namely MAX-DOAS
2. Just curious about the FTIR equipment, the InSb detector for thermal channels while MCT used for middle infrared bands?
Response to Reviewer 1Sent on 21 Mar 2019 by Jie Cheng
LPC2E & LATMOS, CNRS
The author describes a new FTS instrument which is used to measure total atmospheric columns of ozone, carbon monoxide, methane and nitrous oxide. Testing of the instrument is performed, and the instrument appears to have potential to provide good quality data. The instrument is deployed in Beijing during the 2008 Summer Olympic Games in that city, taking daily measurements, and the temporal trends in these trace gas columns are presented.
In general, this is a well-constructed simple paper which outlines and evaluates a new instrument which may be of interest to readers of Sci. The field deployment is relatively simple and limited in scope and is best considered as a test of the instrument rather than a major contribution to the understanding of Beijing’s air quality. My only substantial concern are statements using the observations to assess the outcome of a local policy intervention which I do not believe is justified.
Overall I am happy to recommend approval of this publication. I have a few specific and relatively minor comments and revisions which I outline below:
· The sentence “To data, many satellites have the capability of freely providing the products of the trace gases [2–5]” is badly phrased. I suggest “There exist several satellite products of atmospheric columns of various trace gases [e.g. 2–5]”
· Grammar: change “…the ground-based Fourier Transfer Spectrometer (FTS)…” to “…ground-based Fourier Transfer Spectrometers (FTS)…”.
· “cannot satisfy the requirements of monitoring purpose” change to “cannot satisfy the monitoring requirements”.
· The geographical coordinates should be given to two or three decimal places.
· I suggest adding “in situ” in the description of the “traditional chemistry sampling instruments”.
Atmospheric Trace Gas Measurements section
· The reader should be told what B3M-IR stands for.
· I suggest either or both of a) highlighting the position microwindows from table 1 on Figure 2 or including the SNR for the specified microwindows in a column on Table 1.
· Grammar: change “is start” to “was started” and “end” to “ended”.
· The units of phase error on figure 1b are not specified (degrees, radians?). The y-axis limits for the phase error should be chosen to better display the range of the data.
· “Above this, the mid-latitude Summer atmosphere is used.” – please specify the source of this atmospheric profile.
· Table 1 would benefit from horizontal lines separating the gases.
· Also in table 1 it is unclear if the first and third microwindow for CH4 have no interfering gases or if H2O, O3 and HCl apply for these also. This should be made clear.
· “If the RMS residual value is very small…” – please include a rough numerical value for what “very small” means in this context.
· RMS values should be expressed as numbers rather than % (unless this is the style preference of the journal)
· In Figures 3, 5, and 7 “calculated” is misspelled.
· “…we could not acquire the ozonesonde data.” Change to “we could not acquire ozonesonde data.”
· Please include time zone for the times given. 24-hour format would be preferable.
· 12:00 AM would be interpreted by many readers to mean midnight. To avoid doubt it may be better to write “noon”.
· The date format for figures 12-15 should be changed, MM/DD/YY is not a good format for an international journal. YYYY-MM-DD is preferable (the author may wish to omit the year as all data is from 2008).
· Figures 12-15 show that there is no data for some days. These gaps should be explained in the text.
· The temporal trend in the trace gas concentrations should be quantified – simple trendlines and R2values should be sufficient. Without numerical assessment it is difficult to evaluate the validity of the analysis the author makes.
· I disagree with the author’s assessment that “The total column amount of CO at the end of July, 2008 is the highest, and then it began to decrease gradually.” Figure 13 appears to show a sharp drop after the first few measurements an then a mostly stable profile after this. The data may be too sparse to make strong conclusions about trend, and are certainly too sparse and the trends too weak to make an evaluation of a specific policy. References to the Beijing traffic control policy should be removed.
· Article titles are all in lower case after the first letter, which is incorrect in some gases (e.g. “gome” and “no2”)