scholarly journals High-accuracy continuous airborne measurements of greenhouse gases (CO<sub>2</sub> and CH<sub>4</sub>) using the cavity ring-down spectroscopy (CRDS) technique

2010 ◽  
Vol 3 (2) ◽  
pp. 375-386 ◽  
Author(s):  
H. Chen ◽  
J. Winderlich ◽  
C. Gerbig ◽  
A. Hoefer ◽  
C. W. Rella ◽  
...  
Keyword(s):  
Water Vapor ◽  
Greenhouse Gases ◽  
Ambient Air ◽  
High Accuracy ◽  
Mean Difference ◽  
Pressure Broadening ◽  
Cavity Ring Down Spectroscopy ◽  
Airborne Measurements ◽  
The Mean ◽  
Cavity Ring Down

Abstract. High-accuracy continuous measurements of greenhouse gases (CO2 and CH4) during the BARCA (Balanço Atmosférico Regional de Carbono na Amazônia) phase B campaign in Brazil in May 2009 were accomplished using a newly available analyzer based on the cavity ring-down spectroscopy (CRDS) technique. This analyzer was flown without a drying system or any in-flight calibration gases. Water vapor corrections associated with dilution and pressure-broadening effects for CO2 and CH4 were derived from laboratory experiments employing measurements of water vapor by the CRDS analyzer. Before the campaign, the stability of the analyzer was assessed by laboratory tests under simulated flight conditions. During the campaign, a comparison of CO2 measurements between the CRDS analyzer and a nondispersive infrared (NDIR) analyzer on board the same aircraft showed a mean difference of 0.22±0.09 ppm for all flights over the Amazon rain forest. At the end of the campaign, CO2 concentrations of the synthetic calibration gases used by the NDIR analyzer were determined by the CRDS analyzer. After correcting for the isotope and the pressure-broadening effects that resulted from changes of the composition of synthetic vs. ambient air, and applying those concentrations as calibrated values of the calibration gases to reprocess the CO2 measurements made by the NDIR, the mean difference between the CRDS and the NDIR during BARCA was reduced to 0.05±0.09 ppm, with the mean standard deviation of 0.23±0.05 ppm. The results clearly show that the CRDS is sufficiently stable to be used in flight without drying the air or calibrating in flight and the water corrections are fully adequate for high-accuracy continuous airborne measurements of CO2 and CH4.

scholarly journals High-accuracy continuous airborne measurements of greenhouse gases (CO<sub>2</sub> and CH<sub>4</sub>) during BARCA

2009 ◽  
Vol 2 (6) ◽  
pp. 3127-3152
Author(s):  
H. Chen ◽  
J. Winderlich ◽  
C. Gerbig ◽  
A. Hoefer ◽  
C. W. Rella ◽  
...  
Keyword(s):  
Water Vapor ◽  
Greenhouse Gases ◽  
Ambient Air ◽  
High Accuracy ◽  
Mean Difference ◽  
Pressure Broadening ◽  
Airborne Measurements ◽  
Amazon Rain Forest ◽  
The Mean ◽  
The Stability

Abstract. High-accuracy continuous measurements of greenhouse gases (CO2 and CH4) during the BARCA (Balanço Atmosférico Regional de Carbono na Amazônia) phase B campaign in Brazil in May 2009 were accomplished using a newly available analyzer based on the cavity ring-down spectroscopy (CRDS) technique. This analyzer was flown without a drying system or any in-flight calibration gases. Water vapor corrections associated with dilution and pressure-broadening effects for CO2 and CH4 were derived from laboratory experiments employing measurements of water vapor by the CRDS analyzer. Before the campaign, the stability of the analyzer was assessed by laboratory tests under simulated flight conditions. During the campaign, a comparison of CO2 measurements between the CRDS analyzer and a nondispersive infrared (NDIR) analyzer on board the same aircraft showed a mean difference of 0.22±0.09 ppm for all flights over the Amazon rain forest. At the end of the campaign, CO2 concentrations of the synthetic calibration gases used by the NDIR analyzer were determined by the CRDS analyzer. After correcting for the isotope and the pressure-broadening effects that resulted from changes of the composition of synthetic vs. ambient air, and applying those concentrations as calibrated values of the calibration gases to reprocess the CO2 measurements made by the NDIR, the mean difference between the CRDS and the NDIR during BARCA was reduced to 0.05±0.09 ppm, with the mean standard deviation of 0.23±0.05 ppm. The results clearly show that the CRDS is sufficiently stable to be used in flight without drying the air or calibrating in flight and the water corrections are fully adequate for high-accuracy continuous airborne measurements of CO2 and CH4.

scholarly journals Effect of air composition (N<sub>2</sub>, O<sub>2</sub>, Ar, and H<sub>2</sub>O) on CO<sub>2</sub> and CH<sub>4</sub> measurement by wavelength-scanned cavity ring-down spectroscopy: calibration and measurement strategy

2012 ◽  
Vol 5 (11) ◽  
pp. 2689-2701 ◽  
Author(s):  
H. Nara ◽  
H. Tanimoto ◽  
Y. Tohjima ◽  
H. Mukai ◽  
Y. Nojiri ◽  
...  
Keyword(s):  
Water Vapor ◽  
Ambient Air ◽  
Experimental Results ◽  
Correction Function ◽  
Pressure Broadening ◽  
Cavity Ring Down Spectroscopy ◽  
Significant Difference ◽  
Synthetic Standard ◽  
Background Gas ◽  
Cavity Ring Down

Abstract. We examined potential interferences from water vapor and atmospheric background gases (N2, O2, and Ar), and biases by isotopologues of target species, on accurate measurement of atmospheric CO2 and CH4 by means of wavelength-scanned cavity ring-down spectroscopy (WS-CRDS). Changes of the background gas mole fractions in the sample air substantially impacted the CO2 and CH4 measurements: variation of CO2 and CH4 due to relative increase of each background gas increased as Ar < O2 < N2, suggesting similar relation for the pressure-broadening effects (PBEs) among the background gas. The pressure-broadening coefficients due to variations in O2 and Ar for CO2 and CH4 are empirically determined from these experimental results. Calculated PBEs using the pressure-broadening coefficients are linearly correlated with the differences between the mole fractions of O2 and Ar and their ambient abundances. Although the PBEs calculation showed that impact of natural variation of O2 is negligible on the CO2 and CH4 measurements, significant bias was inferred for the measurement of synthetic standard gases. For gas standards balanced with purified air, the PBEs were estimated to be marginal (up to 0.05 ppm for CO2 and 0.01 ppb for CH4) although the PBEs were substantial (up to 0.87 ppm for CO2 and 1.4 ppb for CH4) for standards balanced with synthetic air. For isotopic biases on CO2 measurements, we compared experimental results and theoretical calculations, which showed excellent agreement within their uncertainty. We derived instrument-specific water correction functions empirically for three WS-CRDS instruments (Picarro EnviroSense 3000i, G-1301, and G-2301), and evaluated the transferability of the water correction function from G-1301 among these instruments. Although the transferability was not proven, no significant difference was found in the water vapor correction function for the investigated WS-CRDS instruments as well as the instruments reported in the past studies within the typical analytical precision at sufficiently low water concentrations (<0.7% for CO2 and <0.6% for CH4). For accurate measurements of CO2 and CH4 in ambient air, we concluded that WS-CRDS measurements should be performed under complete dehumidification of air samples, or moderate dehumidification followed by application of a water vapor correction function, along with calibration by natural air-based standard gases or purified air-balanced synthetic standard gases with the isotopic correction.

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 Impact of Residual Water Vapor on the Simultaneous Measurements of Trace CH4 and N2O in Air with Cavity Ring-Down Spectroscopy

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 221
Author(s):  
Qianhe Wei ◽  
Bincheng Li ◽  
Jing Wang ◽  
Binxing Zhao ◽  
Ping Yang
Keyword(s):  
Water Vapor ◽  
Spectral Range ◽  
Ambient Air ◽  
Residual Water ◽  
Measured Spectrum ◽  
Cavity Ring Down Spectroscopy ◽  
Simultaneous Measurements ◽  
Ch4 And N2o ◽  
The Impact ◽  
Cavity Ring Down

Methane (CH4) and nitrous oxide (N2O) are among the most important atmospheric greenhouse gases. A gas sensor based on a tunable 7.6 μm continuous-wave external-cavity mode-hop-free (EC-MHF) quantum cascade laser (from 1290 to 1350 cm−1) cavity ring-down spectroscopy (CRDS) technique was developed for the simultaneous detection of CH4 and N2O in ambient air with water vapor (H2O) mostly removed via molecular sieve drying to minimize the impact of H2O on the simultaneous measurements. Still, due to the broad and strong absorption spectrum of H2O in the entire mid-infrared (mid-IR) spectral range, residual H2O in the dried ambient air due to incomplete drying and leakage, if not properly accounted for, could cause a significant influence on the measurement accuracy of the simultaneous CH4 and N2O detection. In this paper, the impact of residual H2O on the simultaneous CH4 and N2O measurements were analyzed by comparing the CH4 and N2O concentrations determined from the measured spectrum in the spectral range from 1311 to 1312.1 cm−1 via simultaneous CH4 and N2O measurements and that determined from the measured spectrum in the spectral range from 1311 to 1313 cm−1 via simultaneous CH4, N2O, and H2O measurements. The measured dependence of CH4 and N2O concentration errors on the simultaneously determined H2O concentration indicated that the residual H2O caused an under-estimation of CH4 concentration and over-estimation of N2O concentration. The H2O induced CH4 and N2O concentration errors were approximately linearly proportional to the residual H2O concentration. For the measurement of air flowing at 3 L per min, the residual H2O concentration was stabilized to approximately 14 ppmv, and the corresponding H2O induced errors were −1.3 ppbv for CH4 and 3.7 ppbv for N2O, respectively.

scholarly journals Evaluation of factors affecting accurate measurements of atmospheric CO<sub>2</sub> and CH<sub>4</sub> by wavelength-scanned cavity ring-down spectroscopy

2012 ◽  
Vol 5 (4) ◽  
pp. 5009-5041 ◽  
Author(s):  
H. Nara ◽  
H. Tanimoto ◽  
Y. Tohjima ◽  
H. Mukai ◽  
Y. Nojiri ◽  
...  
Keyword(s):  
Water Vapor ◽  
Theoretical Calculations ◽  
Ambient Air ◽  
Experimental Results ◽  
Correction Function ◽  
Cavity Ring Down Spectroscopy ◽  
Factors Affecting ◽  
Significant Difference ◽  
Synthetic Standard ◽  
Cavity Ring Down

Abstract. We examined potential interferences from water vapor and atmospheric background gases (N2, O2, and Ar), and biases by isotopologues of target species, on accurate measurement of atmospheric CO2 and CH4 by means of wavelength-scanned cavity ring-down spectroscopy (WS-CRDS). Variations in the composition of the background gas substantially impacted the CO2 and CH4 measurements: the measured amounts of CO2 and CH4 decreased with increasing N2 mole fraction, but increased with increasing O2 and Ar, suggesting that the pressure-broadening effects (PBEs) increased as Ar < O2 < N2. Using these experimental results, we inferred PBEs for the measurement of synthetic standard gases. The PBEs were negligible (up to 0.05 ppm for CO2 and 0.01 ppb for CH4) for gas standards balanced with purified air, although the PBEs were substantial (up to 0.87 ppm for CO2 and 1.4 ppb for CH4) for standards balanced with synthetic air. For isotopic biases on CO2 measurements, we compared experimental results and theoretical calculations, which showed excellent agreement within their uncertainty. We derived empirical correction functions for water vapor for three WS-CRDS instruments (Picarro EnviroSense 3000i, G-1301, and G-2301). Although the transferability of the functions was not clear, no significant difference was found in the water vapor correction values among these instruments within the typical analytical precision at sufficiently low water concentrations (< 0.3%V for CO2 and < 0.4%V for CH4). For accurate measurements of CO2 and CH4 in ambient air, we concluded that WS-CRDS measurements should be performed under complete dehumidification of air samples, or moderate dehumidification followed by application of a water vapor correction function, along with calibration by natural air-based standard gases or purified air-balanced synthetic standard gases with isotopic correction.

scholarly journals Validation of spectroscopic gas analyzer accuracy using gravimetric standard gas mixtures: Impact of background gas composition on CO<sub>2</sub> quantitation by cavity ring-down spectroscopy

2017 ◽  
Author(s):  
Jeong Sik Lim ◽  
Miyeon Park ◽  
Jinbok Lee ◽  
Jeongsoon Lee
Keyword(s):  
Ambient Air ◽  
Gas Mixtures ◽  
Gas Composition ◽  
Optical Intensity ◽  
Negative Deviation ◽  
Gas Analyzer ◽  
Pressure Broadening ◽  
Background Gas ◽  
Standard Gas Mixtures ◽  
Cavity Ring Down

Abstract. Effect of background gas composition on the measurement of CO2 levels was investigated by wavelength-scanned cavity ring-down spectrometry (WS-CRDS) employing a spectral line centered at the R(1) of the (3 0° 1)III ← (0 0 0) band. For this purpose, eight cylinders with various gas compositions were gravimetrically and manometrically prepared within 2σ = 0.1 %, and these gas mixtures were introduced into the WS-CRDS analyzer calibrated against standards of ambient air composition. Depending on the gas composition, deviations between CRDS-determined and gravimetrically (or manometrically) assigned CO2 concentrations ranged from −9.77 to 5.36 μmol/mol, e.g., excess N2 exhibited a negative deviation, whereas excess Ar showed a positive one. The total pressure broadening coefficients (TBPCs) obtained from the composition of N2, O2 and Ar thoroughly corrected the deviations up to −0.5–0.6 μmol/mol, while these values were −0.43–1.43 μmol/mol considering PBCs induced by only N2. The use of TBPCs enhanced deviations to be corrected to ~ 0.15 %. Furthermore, the above correction linearly shifted CRDS responses for a wide extent of TPBCs ranging from 0.065 to 0.081 cm−1 atm−1. Thus, accurate measurements using optical intensity-based techniques such as WS-CRDS require TBPC-based instrument calibration.

Trace detection of C2H2 in ambient air using continuous wave cavity ring-down spectroscopy combined with sample pre-concentration

2007 ◽  
Vol 90 (1) ◽  
pp. 1-9 ◽  
Author(s):  
M. Pradhan ◽  
R.E. Lindley ◽  
R. Grilli ◽  
I.R. White ◽  
D. Martin ◽  
...  
Keyword(s):  
Continuous Wave ◽  
Ambient Air ◽  
Trace Detection ◽  
Cavity Ring Down Spectroscopy ◽  
Cavity Ring Down

scholarly journals A cavity ring-down spectroscopy sensor for measurements of gaseous elemental mercury – Part 1: Development for high time resolution measurements in ambient air

2012 ◽  
Vol 5 (6) ◽  
pp. 8995-9020
Author(s):  
A. Pierce ◽  
D. Obrist ◽  
H. Moosmüller ◽  
X. Faïn ◽  
C. Moore
Keyword(s):  
Time Resolution ◽  
Frequency Conversion ◽  
Elemental Mercury ◽  
Ambient Air ◽  
High Time ◽  
High Time Resolution ◽  
Concentration Data ◽  
Cavity Ring Down Spectroscopy ◽  
Gaseous Elemental Mercury ◽  
Cavity Ring Down

Abstract. The ability to make high time resolution measurements of gaseous elemental mercury (GEM) concentrations in air is imperative for the understanding of mercury cycling. Here we describe further development and field implementation of a laboratory prototype pulsed cavity ring-down spectroscopy (CRDS) system for high time resolution, continuous and automated measurement of GEM concentrations in ambient air. In particular, we present use of an external, isotopically enriched Hg cell for automated wavelength locking and wavelength stabilization to maintain laser wavelength on the peak of GEM absorption line in ambient air. We further describe implementation of differential absorption measurements using a piezoelectric tuning element that allows for continuous accounting of system baseline extinction losses needed to calculate GEM absorption coefficients. Data acquisition systems and software programs were modified to acquire high-speed ring-down data at 50 Hz repetition rate as well as process and analyze data in real time. The system was installed in a mobile trailer, and inlet systems and temperature controls were designed to minimize effects of changes in ambient air temperature and ozone (O3) concentration. Data that identify technical challenges and interferences that occurred during measurements, including temperature fluctuations, interferences by ambient O3 and drifts in frequency conversion efficiencies are discussed. Successful development of a CRDS system capable of measuring ambient air GEM concentrations with high time resolution is based on minimizing these interferences.

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