The peroxy radical chemical amplification (PERCA) method is combined with cavity ringdown spectroscopy(CRDS) to detect peroxy radicals (HO2 and RO2). In PERCA, HO2 and RO2 are first converted to NO2 via reactions with NO, and the OH and RO coproducts are recycled back to HO2 in subsequent reactions with CO and O2; the chain reactions of HO2 are repeated and amplify the level of NO2. The amplified NO2 is then monitored by CRDS, a sensitive absorption technique. The PERCA-CRDS method is calibrated using a HO2 radical source (0.5-3 ppbv), which is generated by thermal decomposition of H2O2 vapor (permeated from 2% H2O2 solution through a porous Teflon tubing) up to 600 degrees C. Using a 2-m long 6.35-mm o.d. Teflon tubing as the flow reactor and 2.5 ppmv NO and 2.5-10% vol/vol CO, the PERCA amplification factor or chain length, Delta[NO2]/([HO2]+[RO2]), is determined to be 150 +/- 50 (90% confidence limit) in this study. The peroxy radical detection sensitivity by PERCA-CRDS is estimated to be approximately 10 pptv/60 s (3sigma). Ambient measurements of the peroxy radicals are carried out at Riverside, California in 2007 to demonstrate the PERCA-CRDS technique.
Ambientdetection of NO2 by cavity ring-down spectroscopy is examined in the wavelength region near 405.23 nm, and possible interferences by particulates, water vapor, and carbon dioxide are characterized. Particulates can be efficiently removed by the use of a 0.45 microm fluoropolymer filter. Water vapor has a response of 2.8 ppb (NO2 equivalent) for 1.0% water vapor (80% relative humidity at 10 degrees C) in air at 405.23 nm in a broad continuous absorption feature. Carbon dioxide has a response of 0.8 ppb (NO2 equivalent) for 1.0% CO2 attributable to Rayleigh scattering and would not contribute significant interference in ambient measurements due to the lower ambient CO2 levels. Water vapor interference and in general broad background in the absorption spectrum can be accounted for by removing NO2 selectively in the ambient air stream with an annular denuder coated with sodium hydroxide and methoxyphenol (guiacol). Subtraction of the resulting background signal provides NO2 measurements with a limit of detection of 150 ppt/10 s (SIN = 3). Reliable NO2 measurements could be obtained by this method without the need for frequent calibration with calibration gas. Ambient NO2 measurements are carried out to demonstrate this method.
NO(2) analyzers are much more valuable if they can also measure NO since the two (NO+NO(2)=NO(x)) are often found together. NO can be quantitatively converted to NO(2) by reaction with ozone and subsequent thermal decomposition of the N(2)O(5) that may form from further oxidation. The conversion of NO, along with decomposition of N(2)O(5) and removal of the remaining unreacted ozone with a heated chamber, allows for quantitative determination of NO(x) using a NO(2) analyzer and the determination of decomposed acyl peroxynitrates. Ambient tests are performed to demonstrate these methods.
Abstract. Laboratory measurements of water vapor absorption using cavity ring-down spectroscopy revealed a broad absorption at 405 nm with a quadratic dependence on water monomer concentration, a similar absorption with a linear component at 532 nm, and only linear absorption at 570 nm in the vicinity of water monomer peaks. D2O absorption is weaker and linear at 405 nm. Van't Hoff plots constructed at 405.26 nm suggest that for dimerization, Keq=0.056±0.02 atm−1, ΔH°301 K=−16.6±2 kJ mol−1 and ΔS°301 K=−80±10 J mol−1 K−1. This transition peaks at 409.5 nm, could be attributed to the 8th overtone of water dimer and the 532 nm absorption to the 6th overtone. It is possible that some lower overtones previously searched for are less enhanced. These absorptions could increase water vapor feed back calculations leading to higher global temperature projections with currently projected greenhouse gas levels or greater cooling from greenhouse gas reductions.
We built three successive versions of a thermal decomposition cavity ring-down spectrometer and tested their response to explosives. These explosive compound analyzers successfully detected nitroglycerine, 2,4,6-trinitrotoluene (TNT), pentaerythryl tetranitrate, hexahydro-1,3,5-trinitro-s-triazine and triacetone triperoxide (TATP). We determined the pathlength and limits of detection for each, with the best limit of detection being 13 parts per trillion (ppt) of TNT. For most of the explosive tests, the peak height was higher than the expected value, meaning that peroxy radical chain propagation was occurring with each of the explosives and not just the peroxide TATP.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.