To measure NO in the stratosphere, we need to remove O3 before detection in a dark cell. Some materials such as Na2S2O3 can remove O3 rapidly but it largely affects NO2 and part of NO2 is converted to NO. I'm wondering if there are some methods or techniques that can remove O3 fastly but do not affect NOx. Thank you!
Hi Nick, Thanks for the kind reply. In fact, I should mention that we already have this technique, Optical-feedback cavity-enhanced absorption spectroscopy (OF-CEAS), to quantify NO. However, because the sampling tube and the detection cell are in dark conditions and the residence time in our instrument is 10-20 s, NO will be rapidly oxidized by the high level of O3 of ~8 ppmv in the ozone layer. Hence, we need to remove ozone once the air reaches the sample tube. We tried KI and Na2S2O3, and found that both could fastly remove ozone with very high efficiency and do not absorb NO. But KI+O3 reaction needs water. In the troposphere, KI works well because tropospheric water vapor concentration is high enough but in the stratosphere, H2O level is too low to maintain the KI+O3 reaction. For Na2S2O3 (typically in the form of Na2S2O3*5H2O), we found it can also remove lots of NO2 and 10% was converted to NO.
So, we hope to find some methods to rapidly remove O3 but not affect NOx. We already collected some ideas such as using Ag, Cu, and MnO (coated) tubes. Since we don't know if they will work, we hope to collect more potential materials that may work and then test all of them in our lab.
I found a critical review on the materials that can remove O3. I put its link here in case someone needs.
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Hi Colleen, thanks for the suggestion. We didn't find good absorbents by far since most of them may also remove NOx, for instance, activated carbon. It's will be great if you have some suggestions on absorbents that can specifically remove O3.
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