A novel, cost-effective analytical method for measuring high-resolution vertical profiles of stratospheric trace gases using a GC-ECD
Abstract. The radiative balance of the upper atmosphere is dependent on the magnitude and distribution of greenhouse gases and aerosols in that region of the atmosphere. Climate models predict that with increasing surface temperature, the primary mechanism for transporting tropospheric air into the stratosphere (known as the Brewer-Dobson Circulation) will strengthen, leading to changes in the distribution of atmospheric water vapor, other greenhouse gases, and aerosols in this region. Stratospheric relationships between greenhouse gases and other long-lived trace gases with various photochemical properties (such as N2O, SF6, and chlorofluorocarbons) provide a strong constraint for tracking changes in the stratospheric circulation. Therefore, a cost-effective approach is needed to monitor these trace gases in the stratosphere. In the past decade, the balloon-borne AirCore sampler developed at NOAA/GML has been routinely used to monitor the mole fractions of CO2, CH4, and CO from ground to approximately 25 km above mean sea level. Our recent development work adapted a gas chromatograph coupled with an electron capture detector (GC-ECD) to measure a suite of trace gases (N2O, SF6, CFC-11, CFC-12, H-1211, and CFC-113) in the stratospheric portion of AirCores. This instrument, called the StratoCore-GC-ECD, allows us to retrieve vertical profiles of these molecules at high resolution (5–7 hPa per measurement). We then launched four AirCore flights and analyzed the stratospheric air samples for these trace gases. The results showed consistent and expected tracer-tracer relationships and good agreement with recent aircraft campaign measurements. Our work demonstrates that the StratoCore-GC-ECD system provides a low-cost and robust approach to measuring key stratospheric trace gases in AirCore samples and for evaluating changes in the stratospheric circulation.
Jianghanyang Li et al.
Status: open (until 30 Mar 2023)
- RC1: 'Comment on egusphere-2023-131', Anonymous Referee #1, 03 Mar 2023 reply
Jianghanyang Li et al.
Vertical profiles of stratospheric CFC-11, CFC-12, CFC-113, H-1211, N2O, SF6 mole fractions acquired from four AirCore flights in Eastern Colorado using StratoCore-GC-ECD https://doi.org/10.15138/VA4C-CY20
Jianghanyang Li et al.
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This paper is within the scope of AMT and should be published. There are some confusing sections, discussed further below, but overall the paper does a nice job of explaining a new technique that will improve our understanding of stratospheric circulation and add important measurements for long-term climate relevant gases. They prove that this technique works well and appears easy to add on to already existing infrastructure, and is cost-effective. There is nice agreement with aircraft measurements and any discrepancies are reasonably explained. I look forward to seeing more StratoCore-GC-ECD data in the future. Given that only one section of this paper needs restructuring, it should be accepted with minor revisions.
The main section of the paper that needs improvement is section 2.3 and relevant figures. Section 2.3 was the most confusing of the entire paper and also critical to the verification of this new system. It was hard to follow the steps of the different experiments. In part this was a challenge because of the different language used (test, experiment, etc) along with the two tests (but maybe more?) to study three scientific objectives. This section is important and a restructure would be helpful for the reader to follow the logic. For example, line 160 mentions ‘both experiments’ and then line 192 mentions ‘another set of tests’. Was that related to the first two tests mentioned at the start of the section? If so, set doesn’t make sense since was only two tests. Overall, this section is content heavy and the reader needs a clearer path to follow the important discussion.
Related to Section 2.3, it is really hard to understand what figures 4 and 5 are trying to show. How does figure 4 show us that there is no contamination? What does the CO2 and N2O tell us in 5a? This figure and/or the relevant text to it needs to be reconsidered so the reader doesn’t need to spend the majority of their time trying to understand it.
Section 3 and Figure 6: Is there a reason why the parachute is red? What is the ‘lightweight material’? Is the fact the balloon is off-white important?
Line 268: “data not shown in figure” – Could the comparison between model and observed be done in a supplement if no space in the paper? It is referenced in the conclusion that there is good agreement between model and observations but there is nothing that directly shows that for the reader. The RMSE is given but more information would be nice.
Lines 275-289: Vertical references are given as hPa but the plots are shown as km which is challenging to compare the figure to the text. Perhaps add a second y axis to Figure 9 with hPa?
Line 20: We then launched
Line 44: chlorofluorocarbonsmolecules
Line 114: add degree symbol to 38C
Line 255: “after the descent” – during the descent? After the initial descent? The phrasing as written implies once it is on the ground
Line 299: in Kansas
Line 301: Are you saying the StratoCore data can get higher than the ER-2 or that it covers more of the stratosphere than the ER-2?
Figure 9: Is it possible to outline the symbols to make them easier to see? Or make them larger like in Figure 10.