IRsweep Application Note CO2
ABSTRACT This Application Note discusses the use of the IRcell for surveillance, detection and identification of environmental pollutants and its primary sources.
IRsweep AG Auguste Piccard Hof 1, IQE, HPT 4.1, 8093 Zurich, Switzerland Email: [email protected] Tel: +41 (0)44 586 79 79 www.irsweep.com
IRCELL FOR ENVIRONMENTAL PROTECTION
App. Note 06/16 All rights reserved© 2016
[email protected] +41(0)44 586 79 79
APPLICATION NOTE ENVIRONMENTAL ANALYSIS
Real Time Online process monitoring for pollutants: Environmental Analysis
VOLUME - 160601
App. Note 06/16 All rights reserved© 2016
[email protected] +41(0)44 586 79 79
PROBLEM It is a widely known fact that several environmental problems such as acid rain, the greenhouse effect, and ozone layer destruction are due to various air pollutants generated from automobiles, industry and homes. The above factors contribute to being a major source of urban atmospheric pollution. Pollutants such as nitrogen oxides, carbon monoxide, hydrocarbons and particulates are present in high levels. Hence, in today’s age it is of primary importance to detect these pollutants.
BACKGROUND ENVIRONMENTAL ANALYSIS To date, these gases have been analyzed mostly by using analytical instruments based on IR absorption, UV absorption and chemiluminescence. 1 Some of the pollutants e.g. NO2 have to be quantified at concentrations as low as a few parts per billion calling for highly sensitive methods. Infrared absorption spectroscopy is suitable for such applications, because ro-vibrational absorptions in the infrared are strong. However, the interaction length between the analyte and the probe light still needs to be maximized in order to boost sensitivity. Such increase in path length is typically achieved by the use of multipass cells of Herriot or White type. These cells are readily available, but have a rather large internal volume, which slows down the response time due long gas exchange times. Furthermore, these cells are sensitive to misalignment through temperature change.
star pattern with an optical path length of up to 4 m in a volume of below 40 ml (see Figure 1), resulting in short gas-exchange times. Product Description: With the IRcell, we introduce a multi pass gas cell consisting of only a single, circular mirror. The cell body is at the same time the mirror reflecting the optical beam. The advantage of such a configuration is its robustness towards mechanical stress such as vibrations or temperature changes. With our initial design, we offer an optical path of 4 m. An assembles IRcell-4M is shown in Figure 2. Sub-permille optical noise: Long path transmission measurements with minimum optical noise of 0.05 % RMS can be achieved. Compact design: A quasi 2-dimensional beampattern enables low sample volume for fast gas exchange times.
Figure 1: Opened IRcell with visible optical beam
SOLUTION The IRcell, a monolithic circular multipass gas cell intended for optical trace-gas sensing, achieves compactness and small gas volume by folding the sensing laser beam into a compact star pattern. In order to cope with the demand in the environmental sensing domain, IRsweep (Zürich, Switzerland) has introduced a compact multipass cell, called the IRcell. It consists only of a small, circular mirror that folds the sensing laser beam into a dense 1
REFERENCE CO 2 MEASUREMENTS USING THE IRCELL Carbon dioxide is a greenhouse effect gas, but at the same time it is associated with respiration of bio organisms and the photosynthesis of plants. 1 Thus, measuring CO2 is of particular importance not only to check the levels in the environment but also for measuring or controlling bio-activity.
Noboru Zamazoe and Norio Miura,(1995). Development of Gas Sensors for Environmental Protection. IEEE,18(2).
App. Note 06/16 All rights reserved© 2016
[email protected] +41(0)44 586 79 79
isotopologues are located. The laser beam is shaped with a reflective objective (×15) and a gold-coated offaxis parabolic mirror (OAP), as shown in Figure 3. A second OAP mounted on a 2D translation stage focuses the beam close to the center of a circular multipass cell, which is very similar to the current commercial IRcell-4M. The output beam is detected with a thermoelectrically cooled MCT detector. A path length of 2.2 m was used for the 1 % mixing ratios and an increased length of 4 m was used in the same cell by changing the star pattern in the cell for lower concentrations.
Figure 2: Fully assembled IRcell
The uniqueness of the IRcell is based on two outstanding properties: its single piece construction and the quasi two-dimensional, star-shaped beam pattern. Thanks to the two-dimensional beam pattern, the internal volume of the cell can be kept very low. Therefore, IRsweep can reach an optical path of several meters with a sample volume that is ten-fold smaller than in most competing gas cells, resulting in short gas exchange times. The singlepiece construction makes the IRcell especially robust and invariant to temperature changes.
Figure 3: Layout of the optical setup (40×40 cm) for CO2 isotopologue measurements. (1) Toroidal MPC, (2) QCL, (3) IR detector, (4) reflective objective, (5) OAPs, (6) spherical mirror, and (7) drop-in Ge etalon. Figure reprinted from 2) with permission from the optical society.
EXPERIMENTAL CONDITIONS Isotope ratio measurements of CO2 were performed by Tuzson et al.2 at Empa, Switzerland, determining mixing ratios ranging from 1% to 400 parts per million. A continuous-wave quantum cascade laser (cw-QCL, Alpes Lasers) was used to scan a spectral region of 0.6 cm−1 around 2310 cm−1, where individual lines of the four most abundant CO2
RESULT AND DISCUSSION Figure 4 shows the absorption spectrum observed by the authors of 2): the grey line shows the transmission of the bare cell. The strong fringes are suppressed by adding a patented absorption mask as
2
) Tuzson, B., Mangold, M., Looser, H., Manninen, A., & Emmenegger, L. (2013). Compact multipass optical cell for laser spectroscopy. OSA Publishing, 38(3), 257-259.
App. Note 06/16 All rights reserved© 2016
[email protected] +41(0)44 586 79 79
it is standardly included with the IRcell-4M. The result is shown as the black line.
Figure 4: (black curve) shows the 1 Hz absorption spectrum of CO2 at a mixing ratio of 0.5%, recorded at 27 hPa gas pressure and 216 cm optical path length. Figure reprinted from 2) with permission from the optical society.
Figure 5 shows the Allan variance of the measured CO2 isotope ratio, achieving a value of 0.03 ‰ after 200 seconds averaging which is on par with other state-of-the-art systems.
Figure 5: Allan variance plot of the recorded time series for the oxygen-isotope ratio (O18/O16) of 1% CO2 in synthetic air. Figure reprinted from 2) with permission from the optical society.
App. Note 06/16 All rights reserved© 2016
[email protected] +41(0)44 586 79 79
IRsweep AG Auguste Piccard Hof 1, IQE, HPT 4.1, 8093 Zurich, Switzerland Email: [email protected] Tel: +41 (0)44 586 79 79 www.irsweep.com
IRCELL FOR ENVIRONMENTAL PROTECTION
App. Note 06/16 All rights reserved© 2016
[email protected] +41(0)44 586 79 79
APPLICATION NOTE ENVIRONMENTAL ANALYSIS
Real Time Online process monitoring for pollutants: Environmental Analysis
VOLUME - 160601
App. Note 06/16 All rights reserved© 2016
[email protected] +41(0)44 586 79 79
PROBLEM It is a widely known fact that several environmental problems such as acid rain, the greenhouse effect, and ozone layer destruction are due to various air pollutants generated from automobiles, industry and homes. The above factors contribute to being a major source of urban atmospheric pollution. Pollutants such as nitrogen oxides, carbon monoxide, hydrocarbons and particulates are present in high levels. Hence, in today’s age it is of primary importance to detect these pollutants.
BACKGROUND ENVIRONMENTAL ANALYSIS To date, these gases have been analyzed mostly by using analytical instruments based on IR absorption, UV absorption and chemiluminescence. 1 Some of the pollutants e.g. NO2 have to be quantified at concentrations as low as a few parts per billion calling for highly sensitive methods. Infrared absorption spectroscopy is suitable for such applications, because ro-vibrational absorptions in the infrared are strong. However, the interaction length between the analyte and the probe light still needs to be maximized in order to boost sensitivity. Such increase in path length is typically achieved by the use of multipass cells of Herriot or White type. These cells are readily available, but have a rather large internal volume, which slows down the response time due long gas exchange times. Furthermore, these cells are sensitive to misalignment through temperature change.
star pattern with an optical path length of up to 4 m in a volume of below 40 ml (see Figure 1), resulting in short gas-exchange times. Product Description: With the IRcell, we introduce a multi pass gas cell consisting of only a single, circular mirror. The cell body is at the same time the mirror reflecting the optical beam. The advantage of such a configuration is its robustness towards mechanical stress such as vibrations or temperature changes. With our initial design, we offer an optical path of 4 m. An assembles IRcell-4M is shown in Figure 2. Sub-permille optical noise: Long path transmission measurements with minimum optical noise of 0.05 % RMS can be achieved. Compact design: A quasi 2-dimensional beampattern enables low sample volume for fast gas exchange times.
Figure 1: Opened IRcell with visible optical beam
SOLUTION The IRcell, a monolithic circular multipass gas cell intended for optical trace-gas sensing, achieves compactness and small gas volume by folding the sensing laser beam into a compact star pattern. In order to cope with the demand in the environmental sensing domain, IRsweep (Zürich, Switzerland) has introduced a compact multipass cell, called the IRcell. It consists only of a small, circular mirror that folds the sensing laser beam into a dense 1
REFERENCE CO 2 MEASUREMENTS USING THE IRCELL Carbon dioxide is a greenhouse effect gas, but at the same time it is associated with respiration of bio organisms and the photosynthesis of plants. 1 Thus, measuring CO2 is of particular importance not only to check the levels in the environment but also for measuring or controlling bio-activity.
Noboru Zamazoe and Norio Miura,(1995). Development of Gas Sensors for Environmental Protection. IEEE,18(2).
App. Note 06/16 All rights reserved© 2016
[email protected] +41(0)44 586 79 79
isotopologues are located. The laser beam is shaped with a reflective objective (×15) and a gold-coated offaxis parabolic mirror (OAP), as shown in Figure 3. A second OAP mounted on a 2D translation stage focuses the beam close to the center of a circular multipass cell, which is very similar to the current commercial IRcell-4M. The output beam is detected with a thermoelectrically cooled MCT detector. A path length of 2.2 m was used for the 1 % mixing ratios and an increased length of 4 m was used in the same cell by changing the star pattern in the cell for lower concentrations.
Figure 2: Fully assembled IRcell
The uniqueness of the IRcell is based on two outstanding properties: its single piece construction and the quasi two-dimensional, star-shaped beam pattern. Thanks to the two-dimensional beam pattern, the internal volume of the cell can be kept very low. Therefore, IRsweep can reach an optical path of several meters with a sample volume that is ten-fold smaller than in most competing gas cells, resulting in short gas exchange times. The singlepiece construction makes the IRcell especially robust and invariant to temperature changes.
Figure 3: Layout of the optical setup (40×40 cm) for CO2 isotopologue measurements. (1) Toroidal MPC, (2) QCL, (3) IR detector, (4) reflective objective, (5) OAPs, (6) spherical mirror, and (7) drop-in Ge etalon. Figure reprinted from 2) with permission from the optical society.
EXPERIMENTAL CONDITIONS Isotope ratio measurements of CO2 were performed by Tuzson et al.2 at Empa, Switzerland, determining mixing ratios ranging from 1% to 400 parts per million. A continuous-wave quantum cascade laser (cw-QCL, Alpes Lasers) was used to scan a spectral region of 0.6 cm−1 around 2310 cm−1, where individual lines of the four most abundant CO2
RESULT AND DISCUSSION Figure 4 shows the absorption spectrum observed by the authors of 2): the grey line shows the transmission of the bare cell. The strong fringes are suppressed by adding a patented absorption mask as
2
) Tuzson, B., Mangold, M., Looser, H., Manninen, A., & Emmenegger, L. (2013). Compact multipass optical cell for laser spectroscopy. OSA Publishing, 38(3), 257-259.
App. Note 06/16 All rights reserved© 2016
[email protected] +41(0)44 586 79 79
it is standardly included with the IRcell-4M. The result is shown as the black line.
Figure 4: (black curve) shows the 1 Hz absorption spectrum of CO2 at a mixing ratio of 0.5%, recorded at 27 hPa gas pressure and 216 cm optical path length. Figure reprinted from 2) with permission from the optical society.
Figure 5 shows the Allan variance of the measured CO2 isotope ratio, achieving a value of 0.03 ‰ after 200 seconds averaging which is on par with other state-of-the-art systems.
Figure 5: Allan variance plot of the recorded time series for the oxygen-isotope ratio (O18/O16) of 1% CO2 in synthetic air. Figure reprinted from 2) with permission from the optical society.
App. Note 06/16 All rights reserved© 2016
[email protected] +41(0)44 586 79 79
