The paper “A new site: ground-based FTIR XCO2, XCH4 and XCO measurements at Xianghe, China” by Yang et al. presents one year period of FTIR XCO2, XCH4 and XCO measurements at Xianghe located in North China. The diurnal cycles and seasonal cycles of these gases have been discussed simply by selecting a few days of measurements and the one year period of measurements, respectively. In addition, the FTIR measurements have been compared with the Orbiting Carbon Observatory-2 (OCO-2) and Tropospheric Monitoring Instrument (TROPOMI) satellite observations. Considering that there are few FTIR stations in Asian continent, the XCO2, XCH4 and XCO FTIR measurements at Xianghe will extend useful information for satellite or chemical model validation in the specifics of North China. Language and analysis organized in this version are better than the previous version. However, to be a scientific paper, much work are still needed. Furthermore, this paper only presents measurements in Xianghe and the time period is too short, the discussion, conclusion and contribution to the community are not general representative. Especially, site/methodology and XCH4 time series at Xianghe have been already published elsewhere. Personally, I don’t recommend for publication in Earth System Science Data (ESSD).
Specific comments are listed as:
1. This paper presented detailed descriptions with respect to instrument maintenance, data quality control, retrieval methodology, status of OCO-2 & TROPOMI and comparison methodology. Most of them are pretty standard, and a brief introduction with a reference is sufficient. Especially, the authors described exactly day/time for when they take measurements, perform instrument line shape analysis, replace the solar tracker mirror, and when the nearby meteorology tower block the measurements, etc. These descriptions are more like a maintenance protocol or technical report rather a scientific paper. These descriptions contributed very little to the point of this paper and I suppose that the readers would show little interesting in them.
2. The aims and scope of ESSD state that any interpretation of data is outside the scope of regular articles. Articles on methods describe nontrivial statistical and other methods employed (e.g. to filter, normalize, or convert raw data to primary published data) as well as nontrivial instrumentation or operational methods. Any comparison to other methods is beyond the scope of regular articles. The interpretation of XCO2, XCH4 and XCO FTIR measurements at Xianghe and comparison with OCO-2/TROPOMI seems beyond the scope of this journal.
3. I noticed that a paper entitled “Deriving temporal and vertical distributions of methane in Xianghe using ground-based Fourier transform infrared and gas-analyzer measurements’’ in Advances in Atmospheric Sciences (http://www.iapjournals.ac.cn/aas/en/article/latest) already concluded most site description, methodology, analysis, and conclusion of this paper. Some authors of these two papers are identical. Thus, the data and analysis are not original any more. The authors are always encourage to self-check the quality before submission in case of waste of time.
4. By keeping the technique to achieve the goal of high precision retrieval, extend the time series and the analysis for the regional measurements, and condense the common sense such as retrieval methodology, status of OCO-2 & TROPOMI and comparison methodology, it is possible to accept by a journal focusing on atmospheric technique such as Atmospheric Measurement Techniques. However, the authors should clarify the difference to what they already published in Advances in Atmospheric Sciences.
5. As far as I know, the OCO-2 & TROPOMI were already validated with many years of measurements at many sites. So validate OCO-2 & TROPOMI with one year period of measurements at Xianghe in this paper is a strong argument and I would like to change it to comparison with OCO-2 & TROPOMI observations.
6. In comparison with OCO-2 observations in this study, the satellite measurements are selected within a relax coincident criterion of 5° latitude × 10° longitude around Xianghe, and an overall good agreement was achieved. I would say the local air quality at Xianghe is better than the expected condition.
7. P6line7, FTS should be FTIR or FTIR instrument.