AI Article Synopsis
- The thermal dissociation cavity attenuated phase shift spectroscopy (TD-CAPS) instrument has been enhanced to accurately measure atmospheric total peroxy nitrates (PNs) and organic nitrates (ONs) in high NOx conditions.
- The original TD-CAPS system overestimated concentrations of PNs and ONs due to the conversion of NO to NO2 in heated quartz tubes, caused by peroxy radicals.
- The new system addresses this issue by adding excess ozone to convert NO to NO2 after the quartz tubes, which improved measurement accuracy with less than 20% uncertainty and a detection limit of 0.018 ppbv.
Article Abstract
We improved the thermal dissociation cavity attenuated phase shift spectroscopy (TD-CAPS) instrument to measure atmospheric total peroxy nitrates (PNs) and organic nitrates (ONs) continuously under the condition of high NOx. In TD-CAPS, PNs and ONs are dissociated in heated quartz tubes to form NO2, and the NO2 concentration is measured by cavity attenuated phase shift spectroscopy (CAPS). The original TD-CAPS system overestimates PN and ON concentrations in the presence of high NO concentrations. Our laboratory experiments and numerical simulations showed that the main cause of the overestimation was NO oxidation to NO2 by peroxy radicals generated in the heated quartz tubes. In the improved system, NO was converted to NO2 by adding excess O3 after the quartz tubes so that CAPS detected NOx (NO and NO2) instead of NO2. The uncertainty of the improved system was less than 20% with ∼15 parts per billion by volume (ppbv) NO and ∼80 ppbv NO2. The estimated detection limit (3σ) was 0.018 ppbv with an integration time of 2 min in the presence of 64 ppbv NO2. The improved system was tested for measurement of PNs and ONs in an urban area, and the results indicated that interference from NO was successfully suppressed.
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| http://dx.doi.org/10.1063/5.0172219 | DOI Listing |
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