Development and characterization of a high precision QCLAS for selective NO2 measurement

2020 ◽  
Author(s):  
Nicolas Sobanski ◽  
Beat Schwarzenbach ◽  
Béla Tuzson ◽  
Lukas Emmenegger ◽  
Dave R. Worton ◽  
...  
Keyword(s):  
Nitrogen Dioxide ◽  
High Precision ◽  
Anthropogenic Activities ◽  
Ambient Pressure ◽  
Measurement Techniques ◽  
Ambient Air ◽  
Low Noise ◽  
Pollution Monitoring ◽  
Urban Air ◽  
Custom Made

<p>   Nitrogen dioxide (NO<sub>2</sub>) is an atmospheric pollutant whose emissions are mostly linked to anthropogenic activities. It is, with nitric oxide (NO), the most abundant member of the nitrogen oxides family in tropospheric urban air (mixing ratios up to hundreds of ppbv), with a lifetime ranging from hours to days. NO<sub>2</sub> is well known for its role as a boundary layer ozone and organic nitrates precursor and for affecting the oxidation capacity of the atmosphere. It has thus been subject to emissions mitigation policies and ambient air amount fraction monitoring for a few decades. The latter fully relies on the Chemiluminescence Detection technique (CLD), which is an indirect method measuring NO<sub>2</sub> after conversion to NO.<br>   Recent advances in spectroscopy led to the development of direct and more selective ways to measure NO<sub>2</sub>. The currently running European Metrology for Nitrogen Dioxide (MetNO2) project, involving more than 15 European academic and industrial partners, promises to fill the gap in reliable and complete datasets for laboratory and field testing of those measurement techniques.<br>Here we present the results of a performance investigation of a high precision Quantum Cascade Laser Absorption Spectrometer (QCLAS) for the selective measurement of NO<sub>2</sub> performed in the frame of the MetNO2 project. This instrument is based on a mid-IR QCL emitting at 6 μm and a custom-made, low noise astigmatic Herriott type multipass cell with an effective optical path length of 100 m to measure NO<sub>2</sub> concentration in the low pptv range. We focus on determining precision, long-term stability and potential biases related to sampling conditions such as ambient pressure, temperature and humidity. The QCLAS device is then compared to other direct spectroscopic (CAPS, CRDS, IBBCEAS) and indirect (CLD) techniques. We also report on the results of a three weeks side-by-side field comparison at an urban air monitoring station of the Swiss National Air Pollution Monitoring Network (NABEL), involving the newly developed QCLAS, and commercial CAPS and CLD instruments.<br>   We show that the QCLAS is well suited for monitoring of NO<sub>2</sub> concentration in ambient air and its performances in term of precision and stability surpass those of the CLD device and compete well with other direct measurement techniques.</p>

scholarly journals Comparison of continuous in-situ CO<sub>2</sub> observations at Jungfraujoch using two different measurement techniques

2014 ◽  
Vol 7 (7) ◽  
pp. 7053-7084
Author(s):  
M. F. Schibig ◽  
M. Steinbacher ◽  
B. Buchmann ◽  
I. T. van der Laan-Luijkx ◽  
S. van der Laan ◽  
...  
Keyword(s):  
Materials Science ◽  
Measurement Techniques ◽  
Ambient Air ◽  
Pollution Monitoring ◽  
Smooth Transition ◽  
Research Station ◽  
Short Term ◽  
Technical Problems ◽  
Two Systems ◽  
Data Coverage

Abstract. Since 2004, atmospheric carbon dioxide (CO2) is measured at the High Altitude Research Station Jungfraujoch by the division of Climate and Environmental Physics at the University of Bern (KUP) using a nondispersive infrared gas analyzer (NDIR) in combination with a paramagnetic O2 analyzer. In January 2010, CO2 measurements based on cavity ring down spectroscopy (CRDS) as part of the Swiss National Air Pollution Monitoring Network have been added by the Swiss Federal Laboratories for Materials Science and Technology (Empa). To ensure a smooth transition – a prerequisite when merging two datasets e.g. for trend determinations – the two measurement systems run in parallel for several years. Such a long-term intercomparison also allows identifying potential offsets between the two datasets and getting information about the compatibility of the two systems on different time scales. A good agreement of the seasonality as well as for the short-term variations was observed and to a lesser extent for trend calculations mainly due to the short common period. However, the comparison revealed some issues related to the stability of the calibration gases of the KUP system and their assigned CO2 mole fraction. It was possible to adapt an improved calibration strategy based on standard gas determinations, which lead to better agreement between the two data sets. By excluding periods with technical problems and bad calibration gas cylinders, the average hourly difference (CRDS − NDIR) of the two systems is −0.03 ppm ± 0.25 ppm. Although the difference of the two datasets is in line with the compatibility goal of ±0.1 ppm of the World Meteorological Organization (WMO), the standard deviation is still too high. A significant part of this uncertainty originates from the necessity to switch the KUP system frequently (every 12 min) for 6 min from ambient air to a working gas in order to correct short-term variations of the O2 measurement system. Allowing additionally for signal stabilization after switching the sample, an effective data coverage of only 1/6 for the KUP system is achieved while the Empa system has a nearly complete data coverage. Additionally, different internal volumes and flow rates between the two systems may affect observed differences.

scholarly journals High-precision atmospheric oxygen measurement comparisons between a newly built CRDS analyzer and existing measurement techniques

2019 ◽  
Vol 12 (12) ◽  
pp. 6803-6826
Author(s):  
Tesfaye A. Berhanu ◽  
John Hoffnagle ◽  
Chris Rella ◽  
David Kimhak ◽  
Peter Nyfeler ◽  
...  
Keyword(s):  
High Precision ◽  
Atmospheric Oxygen ◽  
Measurement Techniques ◽  
Ambient Air ◽  
Field Studies ◽  
Research Station ◽  
Mixing Ratio ◽  
Gas Combustion ◽  
Tightly Coupled ◽  
Oxidation Ratio

Abstract. Carbon dioxide and oxygen are tightly coupled in land biosphere CO2–O2 exchange processes, whereas they are not coupled in oceanic exchange. For this reason, atmospheric oxygen measurements can be used to constrain the global carbon cycle, especially oceanic uptake. However, accurately quantifying small (∼1–100 ppm) variations in O2 is analytically challenging due to the very large atmospheric background which constitutes about 20.9 % (∼209 500 ppm) of atmospheric air. Here we present a detailed description of a newly developed high-precision oxygen mixing ratio and isotopic composition analyzer (Picarro G2207) that is based on cavity ring-down spectroscopy (CRDS) as well as to its operating principles; we also demonstrate comprehensive laboratory and field studies using the abovementioned instrument. From the laboratory tests, we calculated a short-term precision (standard error of 1 min O2 mixing ratio measurements) of < 1 ppm for this analyzer based on measurements of eight standard gases analyzed for 2 h, respectively. In contrast to the currently existing techniques, the instrument has an excellent long-term stability; therefore, calibration every 12 h is sufficient to get an overall uncertainty of < 5 ppm. Measurements of ambient air were also conducted at the Jungfraujoch high-altitude research station and the Beromünster tall tower in Switzerland. At both sites, we observed opposing and diurnally varying CO2 and O2 profiles due to different processes such as combustion, photosynthesis, and respiration. Based on the combined measurements at Beromünster tower, we determined height-dependent O2:CO2 oxidation ratios varying between −0.98 and −1.60; these ratios increased with the height of the tower inlet, possibly due to different source contributions such as natural gas combustion, which has a high oxidation ratio, and biological processes, which have oxidation ratios that are relatively lower.

scholarly journals Comparison of continuous in situ CO<sub>2</sub> observations at Jungfraujoch using two different measurement techniques

2015 ◽  
Vol 8 (1) ◽  
pp. 57-68 ◽  
Author(s):  
M. F. Schibig ◽  
M. Steinbacher ◽  
B. Buchmann ◽  
I. T. van der Laan-Luijkx ◽  
S. van der Laan ◽  
...  
Keyword(s):  
Measurement Techniques ◽  
Ambient Air ◽  
Pollution Monitoring ◽  
Smooth Transition ◽  
Research Station ◽  
Data Sets ◽  
Short Term ◽  
Technical Problems ◽  
Two Systems ◽  
Data Coverage

Abstract. Since 2004, atmospheric carbon dioxide (CO2) is being measured at the High Altitude Research Station Jungfraujoch by the division of Climate and Environmental Physics at the University of Bern (KUP) using a nondispersive infrared gas analyzer (NDIR) in combination with a paramagnetic O2 analyzer. In January 2010, CO2 measurements based on cavity ring-down spectroscopy (CRDS) as part of the Swiss National Air Pollution Monitoring Network were added by the Swiss Federal Laboratories for Materials Science and Technology (Empa). To ensure a smooth transition – a prerequisite when merging two data sets, e.g., for trend determinations – the two measurement systems run in parallel for several years. Such a long-term intercomparison also allows the identification of potential offsets between the two data sets and the collection of information about the compatibility of the two systems on different time scales. A good agreement of the seasonality, short-term variations and, to a lesser extent mainly due to the short common period, trend calculations is observed. However, the comparison reveals some issues related to the stability of the calibration gases of the KUP system and their assigned CO2 mole fraction. It is possible to adapt an improved calibration strategy based on standard gas determinations, which leads to better agreement between the two data sets. By excluding periods with technical problems and bad calibration gas cylinders, the average hourly difference (CRDS – NDIR) of the two systems is −0.03 ppm ± 0.25 ppm. Although the difference of the two data sets is in line with the compatibility goal of ±0.1 ppm of the World Meteorological Organization (WMO), the standard deviation is still too high. A significant part of this uncertainty originates from the necessity to switch the KUP system frequently (every 12 min) for 6 min from ambient air to a working gas in order to correct short-term variations of the O2 measurement system. Allowing additional time for signal stabilization after switching the sample, an effective data coverage of only one-sixth for the KUP system is achieved while the Empa system has a nearly complete data coverage. Additionally, different internal volumes and flow rates may affect observed differences.

scholarly journals Folded tubular photometer for atmospheric measurements of NO<sub>2</sub> and NO

2018 ◽  
Vol 11 (5) ◽  
pp. 2821-2835 ◽  
Author(s):  
John W. Birks ◽  
Peter C. Andersen ◽  
Craig J. Williford ◽  
Andrew A. Turnipseed ◽  
Stanley E. Strunk ◽  
...  
Keyword(s):  
Nitrogen Dioxide ◽  
Black Carbon ◽  
Direct Measurement ◽  
Dynamic Range ◽  
Measurement Techniques ◽  
Ambient Air ◽  
Atmospheric Measurements ◽  
Direct Measurements ◽  
Path Lengths ◽  
Cell Volumes

Abstract. We describe and characterize a modular folded tubular photometer for making direct measurements of the concentrations of nitrogen dioxide (NO2) and specify how this method could be extended to measure other pollutants such as sulfur dioxide (SO2), ozone (O3), and black carbon particulate matter. Direct absorbance measurements using this photometer can be made across the spectral range from the ultraviolet (UV) to the near infrared. The absorbance cell makes use of modular components (tubular detection cells and mirror cubes) that allow construction of path lengths of up to 2 m or more while maintaining low cell volumes. The long path lengths and low cell volumes enable sensitive detection of ambient air pollutants down to low part-per-billion levels for gas species and aerosol extinctions down to 1 Mm−1, corresponding to ∼ 0.1 µg m−3 for black carbon particulates. Pressure equalization throughout the stages of the absorbance measurement is shown to be critical to accurate measurements of analyte concentrations. The present paper describes the application of this photometer to direct measurements of nitrogen dioxide (NO2) and the incorporation of design features that also enable measurement of nitric oxide (NO) in the same instrument. Excellent agreement for ambient measurements along an urban roadside was found for both NO2 and NO measured by the folded tubular photometer compared to existing standard techniques. Compared to commonly used methods for measurements of NOx species, the advantages of this approach include (1) an absolute quantification for NO2 based on the Beer–Lambert law, thereby greatly reducing the frequency at which calibrations are required; (2) the direct measurement of NO2 concentration without prior conversion to NO as is required for the commonly used chemiluminescence method; (3) the use of modular components that allow construction of absorbance detection cells of varying lengths for extending the dynamic range of concentrations that can be measured; (4) a more economical instrument than other currently available direct measurement techniques for NO2; and (5) the potential for simultaneous detection of additional species such as SO2, O3, and black carbon in the same instrument. In contrast to other commercially available direct NO2 measurements, such as cavity-attenuated phase-shift spectroscopy (CAPS), the folded tubular photometer also measures NO simultaneously in the same apparatus by quantitatively converting NO to NO2 with ozone, which is then detected by direct absorbance.

scholarly journals Folded Tubular Photometer for atmospheric measurements of NO<sub>2</sub> and NO

2018 ◽  
Author(s):  
John W. Birks ◽  
Peter C. Andersen ◽  
Craig J. Williford ◽  
Andrew A. Turnipseed ◽  
Stanley E. Strunk ◽  
...  
Keyword(s):  
Nitrogen Dioxide ◽  
Black Carbon ◽  
Direct Measurement ◽  
Air Pollutants ◽  
Measurement Techniques ◽  
Ambient Air ◽  
Atmospheric Measurements ◽  
Direct Measurements ◽  
Path Lengths ◽  
Cell Volumes

Abstract. We describe and characterize a modular Folded Tubular Photometer for making direct measurements of the concentrations of air pollutants such as nitrogen dioxide (NO2), sulfur dioxide (SO2), ozone (O3), and black carbon particulate matter. Direct absorbance measurements using this photometer can be made across the spectral range from the ultraviolet (UV) to the near-infrared. The absorbance cell makes use of modular components (tubular detection cells and mirror cubes) that allow construction of path lengths of up to 2 meters or more while maintaining low cell volumes. The long path lengths and low cell volumes enable sensitive detection of ambient air pollutants down to low part-per-billion levels for gas species and aerosol extinctions down to 1 Mm−1, corresponding to ~ 0.1 μg m−3 for black carbon particulates. Pressure equalization throughout the stages of the absorbance measurement is shown to be critical to accurate measurements of analyte concentrations. The present paper describes the application of this photometer to direct measurements of nitrogen dioxide (NO2) and the incorporation of design features that also enable measurement of nitric oxide (NO) in the same instrument. Excellent agreement for ambient measurements along an urban roadside was found for both NO2 and NO measured by the Folded Tubular Photometer compared to existing standard techniques. Compared to commonly used methods for measurements of NOx species, the advantages of this approach include 1) an absolute quantification for NO2 based on the Beer-Lambert Law, thereby greatly reducing the frequency at which calibrations are required; 2) the direct measurement of NO2 concentration without prior conversion to NO as is required for the commonly used chemiluminescence method; 3) the use of modular components that allow construction of absorbance detection cells of varying lengths for extending the dynamic range of concentrations that can be measured; 4) a more economical instrument than other currently available direct measurement techniques for NO2; and 5) the potential for simultaneous detection of additional species such as SO2, O3, and black carbon in the same instrument. In contrast to other commercially available direct NO2 measurements, such as cavity-attenuated phase shift spectroscopy (CAPS), the Folded Tubular Photometer provides a means for measuring NO simultaneously in the same apparatus by quantitatively converting NO to NO2 with ozone, which is then detected by direct absorbance.

scholarly journals Advances in High-Precision NO2 Measurement by Quantum Cascade Laser Absorption Spectroscopy

2021 ◽  
Vol 11 (3) ◽  
pp. 1222
Author(s):  
Nicolas Sobanski ◽  
Béla Tuzson ◽  
Philipp Scheidegger ◽  
Herbert Looser ◽  
André Kupferschmid ◽  
...  
Keyword(s):  
High Precision ◽  
Quantum Cascade Laser ◽  
Air Pollutant ◽  
Pollution Monitoring ◽  
Visible Range ◽  
Chemiluminescence Detection ◽  
Promising Alternative ◽  
Detection Techniques ◽  
Quantum Cascade ◽  
Custom Made

Nitrogen dioxide (NO2) is a major tropospheric air pollutant. Its concentration in the atmosphere is most frequently monitored indirectly by chemiluminescence detection or using direct light absorption in the visible range. Both techniques are subject to known biases from other trace gases (including water vapor), making accurate measurements at low concentration very challenging. Selective measurements of NO2 in the mid-infrared have been proposed as a promising alternative, but field deployments and comparisons with established techniques remain sparse. Here, we describe the development and validation of a quantum cascade laser-based spectrometer (QCLAS). It relies on a custom-made astigmatic multipass absorption cell and a recently developed low heat dissipation laser driving and a FPGA based data acquisition approach. We demonstrate a sub-pptv precision (1 σ) for NO2 after 150 s integration time. The instrument performance in terms of long-term stability, linearity and field operation capability was assessed in the laboratory and during a two-week inter-comparison campaign at a suburban air pollution monitoring station. Four NO2 instruments corresponding to three different detection techniques (chemiluminescence detection (CLD), cavity-attenuated phase shift (CAPS) spectroscopy and QCLAS) were deployed after calibrating them with three different referencing methods: gas-phase titration of NO, dynamic high-concentration cylinder dilution and permeation. These measurements show that QCLAS is an attractive alternative for high-precision NO2 monitoring. Used in dual-laser configuration, its capabilities can be extended to NO, thus allowing for unambiguous quantification of nitrogen oxides (NOx), which are of key importance in air quality assessments.

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