scholarly journals Trace explosives detection by cavity ring-down spectroscopy (CRDS)

2021 ◽  
Author(s):  
Bobbi Stromer ◽  
Anthony Bednar ◽  
Milo Janjic ◽  
Scott Becker ◽  
Tamara Kylloe ◽  
...  
Keyword(s):  
Thermal Decomposition ◽  
Limit Of Detection ◽  
Peroxy Radical ◽  
Peak Height ◽  
Expected Value ◽  
Explosives Detection ◽  
Triacetone Triperoxide ◽  
Radical Chain ◽  
Cavity Ring Down Spectroscopy ◽  
Cavity Ring Down

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.

scholarly journals Cavity ring-down spectroscopy sensor for detection of hydrogen chloride

2013 ◽  
Vol 6 (4) ◽  
pp. 7217-7250
Author(s):  
C. L. Hagen ◽  
B. C. Lee ◽  
I. S. Franka ◽  
J. L. Rath ◽  
T. C. VandenBoer ◽  
...  
Keyword(s):  
Hydrogen Chloride ◽  
Near Infrared ◽  
Limit Of Detection ◽  
Optical Cavity ◽  
High Specificity ◽  
Ionization Mass ◽  
Cavity Ring Down Spectroscopy ◽  
Mist Chamber ◽  
Hcl Concentration ◽  
Cavity Ring Down

Abstract. A laser-based cavity ring-down spectroscopy (CRDS) sensor for measurement of hydrogen chloride (HCl) has been developed and characterized. The instrument uses light from a distributed-feedback diode laser at 1742 nm coupled to a high finesse optical cavity to make sensitive and quantifiable concentration measurements of HCl based on optical absorption. The instrument has a (1σ) limit of detection of < 20 pptv in 1 min and has high specificity to HCl. The measurement response time to changes in input HCl concentration is < 15 s. Validation studies with a previously calibrated permeation tube setup show an accuracy of better than 10%. The CRDS sensor was preliminarily tested in the field with two other HCl instruments (mist chamber and chemical ionization mass spectrometry), all of which were in broad agreement. The mist chamber and CRDS sensors both showed a 400 pptv plume within 50 pptv agreement. The sensor also allows simultaneous sensitive measurements of water and methane, and minimal hardware modification would allow detection of other near-infrared absorbers.

scholarly journals An intercomparison of HO<sub>2</sub> measurements by Fluorescence Assay by Gas Expansion and Cavity Ring–Down Spectroscopy within HIRAC (Highly Instrumented Reactor for Atmospheric Chemistry)

2017 ◽  
Author(s):  
Lavinia Onel ◽  
Alexander Brennan ◽  
Michele Gianella ◽  
Grace Ronnie ◽  
Ana Lawry Aguila ◽  
...  
Keyword(s):  
Water Vapour ◽  
Atmospheric Chemistry ◽  
Total Pressure ◽  
Limit Of Detection ◽  
Fluorescence Assay ◽  
Fluorescence Signal ◽  
Cavity Ring Down Spectroscopy ◽  
Gas Expansion ◽  
Good Agreement ◽  
Cavity Ring Down

Abstract. The HO2 radical was monitored simultaneously using two independent techniques in the Leeds HIRAC atmospheric simulation chamber at room temperature and total pressures of 150 mbar and 1000 mbar of synthetic air. In the first method, HO2 was measured indirectly following sampling through a pinhole expansion to 3 mbar when sampling from 1000 mbar and 1 mbar when sampling from 150 mbar, with subsequent addition of NO to convert it to OH which was detected via laser-induced fluorescence spectroscopy using the FAGE (fluorescence assay by gas expansion) technique. The FAGE method is used widely to measure HO2 concentrations in the field, and was calibrated using the 185 nm photolysis of water vapour in synthetic air with a limit of detection at 1000 mbar of 1.6 × 106 molecule cm−3 for an averaging time of 30 s. In the second method, HO2 was measured directly and absolutely without the need for a calibration using Cavity Ring Down Spectroscopy (CRDS) with the optical path across the entire ~ 1.4 m width of the chamber, with excitation of the first O-H overtone at 1506.43 nm using a diode laser, and with a sensitivity determined from an Allan deviation plot of 3.0 × 108 and 1.5 x 109 molecule cm−3 at 150 mbar and 1000 mbar, respectively, for an averaging period of 30 s. HO2 was generated in HIRAC by the photolysis of Cl2 using black lamps in the presence of methanol in synthetic air and was monitored by FAGE and CRDS for ~ 5–10 minute periods with the lamps on and also during the HO2 decay after the lamps were switched off. At 1000 mbar total pressure the correlation plot of [HO2]FAGE versus [HO2]CRDS gave a gradient of 0.836 ± 0.004 for HO2 concentrations in the range ~ 4–100 × 109 molecule  cm−3 while at 150 mbar total pressure the corresponding gradient was 0.903 ± 0.002 for HO2 concentrations in the range ~ 6–750 × 108 molecule cm−3. For the period after the lamps were switched off, the second-order decay of the HO2 FAGE signal via its self-reaction was used to calculate the FAGE calibration constant for both 150 and 1000 mbar total pressure. This enabled a calibration of the FAGE method at 150 mbar, an independent measurement of the FAGE calibration at 1000 mbar, and an independent determination of the HO2 cross section at 1506.43 nm, σHO2, at both pressures. For CRDS, the HO2 concentration obtained using σHO2 determined using previous reported spectral data for HO2 and the kinetic decay of HO2 method agreed to within 20 and 12 % at 150 and 1000 mbar, respectively. For the FAGE method a very good agreement (difference within 8 %) has been obtained at 1000 mbar between the water vapour calibration method and the kinetic decay of the HO2 fluorescence signal method. This is the first intercomparison for HO2 between FAGE and CRDS methods, and the good agreement between HO2 concentrations measured using the indirect FAGE method and the direct CRDS method provides a validation for the FAGE method, which is used widely for field measurements of HO2 in the atmosphere.

Thermal decomposition rate of N2O5measured by cavity ring-down spectroscopy

2008 ◽  
Vol 40 (10) ◽  
pp. 679-684 ◽  
Author(s):  
Tomoyuki Ide ◽  
Tomoki Nakayama ◽  
Kenshi Takahashi ◽  
Yutaka Matsumi
Keyword(s):  
Thermal Decomposition ◽  
Decomposition Rate ◽  
Cavity Ring Down Spectroscopy ◽  
Cavity Ring Down

scholarly journals Quantification of peroxynitric acid and peroxyacyl nitrates using an ethane-based thermal dissociation peroxy radical chemical amplification cavity ring-down spectrometer

2018 ◽  
Vol 11 (7) ◽  
pp. 4109-4127
Author(s):  
Youssef M. Taha ◽  
Matthew T. Saowapon ◽  
Faisal V. Assad ◽  
Connie Z. Ye ◽  
Xining Chen ◽  
...  
Keyword(s):  
Limit Of Detection ◽  
Thermal Dissociation ◽  
Peroxy Radical ◽  
Ambient Air ◽  
Oh Radicals ◽  
Ionization Mass ◽  
Chemical Amplification ◽  
Peroxynitric Acid ◽  
Peroxyacyl Nitrates ◽  
Cavity Ring Down

Abstract. Peroxy and peroxyacyl nitrates (PNs and PANs) are important trace gas constituents of the troposphere which are challenging to quantify by differential thermal dissociation with NO2 detection in polluted (i.e., high-NOx) environments. In this paper, a thermal dissociation peroxy radical chemical amplification cavity ring-down spectrometer (TD-PERCA-CRDS) for sensitive and selective quantification of total peroxynitrates (ΣPN  =  ΣRO2NO2) and of total peroxyacyl nitrates (ΣPAN  =  ΣRC(O)O2NO2) is described. The instrument features multiple detection channels to monitor the NO2 background and the ROx ( =  HO2 + RO2 + ΣRO2) radicals generated by TD of ΣPN and/or ΣPAN. Chemical amplification is achieved through the addition of 0.6 ppm NO and 1.6 % C2H6 to the inlet. The instrument's performance was evaluated using peroxynitric acid (PNA) and peroxyacetic or peroxypropionic nitric anhydride (PAN or PPN) as representative examples of ΣPN and ΣPAN, respectively, whose abundances were verified by iodide chemical ionization mass spectrometry (CIMS). The amplification factor or chain length increases with temperature up to 69 ± 5 and decreases with analyte concentration and relative humidity (RH). At inlet temperatures above 120 and 250 °C, respectively, PNA and ΣPAN fully dissociated, though their TD profiles partially overlap. Furthermore, interference from ozone (O3) was observed at temperatures above 150 °C, rationalized by its partial dissociation to O atoms which react with C2H6 to form C2H5 and OH radicals. Quantification of PNA and ΣPAN in laboratory-generated mixtures containing O3 was achieved by simultaneously monitoring the TD-PERCA responses in multiple parallel CRDS channels set to different temperatures in the 60 to 130 °C range. The (1 s, 2σ) limit of detection (LOD) of TD-PERCA-CRDS is 6.8 pptv for PNA and 2.6 pptv for ΣPAN and significantly lower than TD-CRDS without chemical amplification. The feasibility of TD-PERCA-CRDS for ambient air measurements is discussed.

scholarly journals Cavity ring-down spectroscopy sensor for detection of hydrogen chloride

2014 ◽  
Vol 7 (2) ◽  
pp. 345-357 ◽  
Author(s):  
C. L. Hagen ◽  
B. C. Lee ◽  
I. S. Franka ◽  
J. L. Rath ◽  
T. C. VandenBoer ◽  
...  
Keyword(s):  
Hydrogen Chloride ◽  
Near Infrared ◽  
Limit Of Detection ◽  
Optical Cavity ◽  
High Specificity ◽  
Ionization Mass ◽  
Cavity Ring Down Spectroscopy ◽  
Mist Chamber ◽  
Hcl Concentration ◽  
Cavity Ring Down

Abstract. A laser-based cavity ring-down spectroscopy (CRDS) sensor for measurement of hydrogen chloride (HCl) has been developed and characterized. The instrument uses light from a distributed-feedback diode laser at 1742 nm coupled to a high finesse optical cavity to make sensitive and quantifiable concentration measurements of HCl based on optical absorption. The instrument has a (1σ) limit of detection of <20 pptv in 1 min and has high specificity to HCl. The measurement response time to changes in input HCl concentration is <15 s. Validation studies with a previously calibrated permeation tube setup show an accuracy of better than 10%. The CRDS sensor was preliminarily tested in the field with two other HCl instruments (mist chamber and chemical ionization mass spectrometry), all of which were in broad agreement. The mist chamber and CRDS sensors both showed a 400 pptv plume within 50 pptv agreement. The sensor also allows simultaneous sensitive measurements of water and methane, and minimal hardware modification would allow detection of other near-infrared absorbers.

scholarly journals An intercomparison of HO<sub>2</sub> measurements by fluorescence assay by gas expansion and cavity ring-down spectroscopy within HIRAC (Highly Instrumented Reactor for Atmospheric Chemistry)

2017 ◽  
Vol 10 (12) ◽  
pp. 4877-4894 ◽  
Author(s):  
Lavinia Onel ◽  
Alexander Brennan ◽  
Michele Gianella ◽  
Grace Ronnie ◽  
Ana Lawry Aguila ◽  
...  
Keyword(s):  
Water Vapour ◽  
Atmospheric Chemistry ◽  
Total Pressure ◽  
Limit Of Detection ◽  
Fluorescence Assay ◽  
Fluorescence Signal ◽  
Cavity Ring Down Spectroscopy ◽  
Gas Expansion ◽  
Good Agreement ◽  
Cavity Ring Down

Abstract. The HO2 radical was monitored simultaneously using two independent techniques in the Leeds HIRAC (Highly Instrumented Reactor for Atmospheric Chemistry) atmospheric simulation chamber at room temperature and total pressures of 150 and 1000 mbar of synthetic air. In the first method, HO2 was measured indirectly following sampling through a pinhole expansion to 3 mbar when sampling from 1000 mbar and to 1 mbar when sampling from 150 mbar. Subsequent addition of NO converted it to OH, which was detected via laser-induced fluorescence spectroscopy using the FAGE (fluorescence assay by gas expansion) technique. The FAGE method is used widely to measure HO2 concentrations in the field and was calibrated using the 185 nm photolysis of water vapour in synthetic air with a limit of detection at 1000 mbar of 1.6 × 106 molecule cm−3 for an averaging time of 30 s. In the second method, HO2 was measured directly and absolutely without the need for calibration using cavity ring-down spectroscopy (CRDS), with the optical path across the entire ∼ 1.4 m width of the chamber, with excitation of the first O-H overtone at 1506.43 nm using a diode laser and with a sensitivity determined from Allan deviation plots of 3.0 × 108 and 1.5 × 109 molecule cm−3 at 150 and 1000 mbar respectively, for an averaging period of 30 s. HO2 was generated in HIRAC by the photolysis of Cl2 using black lamps in the presence of methanol in synthetic air and was monitored by FAGE and CRDS for ∼ 5–10 min periods with the lamps on and also during the HO2 decay after the lamps were switched off. At 1000 mbar total pressure the correlation plot of [HO2]FAGE versus [HO2]CRDS gave an average gradient of 0.84 ± 0.08 for HO2 concentrations in the range ∼ 4–100 × 109 molecule cm−3, while at 150 mbar total pressure the corresponding gradient was 0.90 ± 0.12 on average for HO2 concentrations in the range ∼ 6–750  ×  108 molecule cm−3.For the period after the lamps were switched off, the second-order decay of the HO2 FAGE signal via its self-reaction was used to calculate the FAGE calibration constant for both 150 and 1000 mbar total pressure. This enabled a calibration of the FAGE method at 150 mbar, an independent measurement of the FAGE calibration at 1000 mbar and an independent determination of the HO2 cross section at 1506.43 nm, σHO2, at both pressures. For CRDS, the HO2 concentration obtained using σHO2, determined using previous reported spectral data for HO2, and the kinetic decay of HO2 method agreed to within 20 and 12 % at 150 and 1000 mbar respectively. For the FAGE method a very good agreement (difference within 8 %) has been obtained at 1000 mbar between the water vapour calibration method and the kinetic decay of the HO2 fluorescence signal method. This is the first intercomparison of HO2 between the FAGE and CRDS methods, and the good agreement between HO2 concentrations measured using the indirect FAGE method and the direct CRDS method provides validation for the FAGE method, which is used widely for field measurements of HO2 in the atmosphere.

scholarly journals Airborne measurement of peroxy radicals using chemical amplification coupled with cavity ring-down spectroscopy: the PeRCEAS instrument

2020 ◽  
Vol 13 (5) ◽  
pp. 2577-2600 ◽  
Author(s):  
Midhun George ◽  
Maria Dolores Andrés Hernández ◽  
Vladyslav Nenakhov ◽  
Yangzhuoran Liu ◽  
John Philip Burrows
Keyword(s):  
Oxidation Mechanism ◽  
Peroxy Radical ◽  
Ambient Air ◽  
Peroxy Radicals ◽  
Free Troposphere ◽  
Cavity Ring Down Spectroscopy ◽  
Airborne Measurements ◽  
Dual Channel ◽  
Unpaired Spin ◽  
Cavity Ring Down

Abstract. Hydroperoxyl (HO2) and organic peroxy (RO2) radicals have an unpaired spin and are highly reactive free radicals. Measurements of the sum of HO2 and RO2 provide unique information about the chemical processing in an air mass. This paper describes the experimental features and capabilities of the Peroxy Radical Chemical Enhancement and Absorption Spectrometer (PeRCEAS). This is an instrument designed to make measurements on aircraft from the boundary layer to the lower stratosphere. PeRCEAS combines the amplified conversion of peroxy radicals to nitrogen dioxide (NO2) with the sensitive detection of NO2 using cavity ring-down spectroscopy (CRDS) at 408 nm. PeRCEAS is a dual-channel instrument, with two identical reactor–detector lines working out of phase with one another at a constant and defined pressure lower than ambient at the aircraft altitude. The suitability of PeRCEAS for airborne measurements in the free troposphere was evaluated by extensive characterisation and calibration under atmospherically representative conditions in the laboratory. The use of alternating modes of the two instrumental channels successfully captures short-term variations in the sum of peroxy radicals, defined as RO2∗ (RO2∗=HO2+∑RO2+OH+∑RO, with R being an organic chain) in ambient air. For a 60 s measurement, the RO2∗ detection limit is < 2 pptv for a minimum (2σ) NO2 detectable mixing ratio < 60 pptv, under laboratory conditions in the range of atmospheric pressures and temperatures expected in the free troposphere. PeRCEAS has been successfully deployed within the OMO (Oxidation Mechanism Observations) and EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional and Global scales) missions in different airborne campaigns aboard the High Altitude LOng range research aircraft (HALO) for the study of the composition of the free troposphere.

scholarly journals Quantification of peroxynitric acid and peroxyacyl nitrates using an ethane-based thermal dissociation peroxy radical chemical amplification cavity ring-down spectrometer

2018 ◽  
Author(s):  
Youssef M. Taha ◽  
Matthew T. Saowapon ◽  
Faisal V. Assad ◽  
Connie Z. Ye ◽  
Xining Chen ◽  
...  
Keyword(s):  
Limit Of Detection ◽  
Thermal Dissociation ◽  
Peroxy Radical ◽  
Ambient Air ◽  
Oh Radicals ◽  
Ionization Mass ◽  
Chemical Amplification ◽  
Peroxynitric Acid ◽  
Peroxyacyl Nitrates ◽  
Cavity Ring Down

Abstract. Peroxy and peroxyacyl nitrates (PNs and PANs) are important trace gas constituents of the troposphere which are challenging to quantify by differential thermal dissociation with NO2 detection in polluted (i.e., high-NOx) environments. In this paper, a thermal dissociation peroxy radical chemical amplification cavity ring-down spectrometer (TD-PERCA-CRDS) for sensitive and selective quantification of total peroxynitrates (ΣPN = ΣRO2NO2) and of total peroxyacyl nitrates (ΣPAN = ΣRC(O)O2NO2) is described. The instrument features multiple detection channels to monitor the NO2 background and the ROx (= HO2 + RO2 + ΣRO2) radicals generated by TD of ΣPN and/or ΣPAN. Chemical amplification is achieved through addition of 0.6 ppm NO and 1.6 % C2H6 to the inlet. The instrument's performance was evaluated using peroxynitric acid (PNA) and peroxyacetic or peroxypropionic nitric anhydride (PAN or PPN) as representative examples of ΣPN and ΣPAN, respectively, whose abundances were verified by iodide chemical ionization mass spectrometry (CIMS). The amplification factor or chain length increases with temperature up to 69 ± 5 and decreases with analyte concentration and relative humidity (RH). At inlet temperatures above 120 °C and 250 °C, respectively, PNA and ΣPAN fully dissociated, though their TD profiles partially overlap. Furthermore, interference from ozone (O3) was observed at temperatures above 150 °C, rationalized by its partial dissociation to O atoms which react with C2H6 to form C2H5 and OH radicals. Quantification of PNA and ΣPAN in laboratory-generated mixtures containing O3 was achieved by simultaneously monitoring the TD-PERCA responses in multiple parallel CRDS channels set to different temperatures in the 60 °C to 130 °C range. The (1 s, 1σ) limit of detection (LOD) of TD-PERCA-CRDS is 3.4 pptv for PNA and 1.3 pptv for ΣPAN and significantly lower than TD-CRDS without chemical amplification. The feasibility of TD-PERCA-CRDS for ambient air measurements is discussed.

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