Non-dispersive Infrared Research Articles

VCSEL-Based Atmospheric Trace Gas Sensor Using First Harmonic Detection

This paper presents a measurement system based on the first harmonic in tunable diode laser absorption spectroscopy using a vertical-cavity surface-emitting laser to measure the atmospheric CO2 and H2O concentrations. The developed system separates the residual amplitude modulation signal from the harmonics and then eliminates it. A digital signal processing is developed to autonomously infer the wavelength and light intensities of the laser. The gas concentrations are determined without extra calibration. The long-term measurements are taken to validate the precision and accuracy of the system. Based on the Allan variance analysis, the broad wavelength scanning enhances the measurement precision, and the first-harmonic detection can achieve about two times as high precision as the traditional second-harmonic detection. The field measurements implemented in early spring of 2018 in Munich were compared with the commercial nondispersive infrared (NDIR) sensor. The outcomes have revealed that our system has high accuracy for the gas concentration measurements and high consistency with the NDIR sensor. The diurnal variations of CO2 concentration have demonstrated that CO2 concentration in urban areas is affected by the biosphere and meteorological conditions and the daily anthropogenic activities. Furthermore, the air trajectory analysis based on the HYSPLIT model has found that the CO2 emission sources primarily come from the southeast of Munich. The developed system described in this paper has a great potential for in situ trace gas concentration measurements, the analysis on the polluted gas distributions, and the verification of the pollutant transport model in urban areas.

Breakthrough in CO2 Measurement With a Chamberless NDIR Optical Gas Sensor

CO2 measurement using the nondispersive infrared (NDIR) gas sensing method is conventionally performed using a gas chamber as the main part of the sensor. In this paper, we report on a novel approach using a light source with an embedded parabolic reflector to measure CO2 concentrations above 400 ppm without the need for a chamber. Four alternative structures for CO2 detection were fabricated that combine gold-coated reflective surfaces and a parabolic reflector with a light source and detector. These simple and cost-effective structures were exposed to CO2 at 400–2200 ppm. The results show linear, accurate, and repeatable calibration curves at different CO2 concentrations. The proposed chamberless structure simplifies the industrial use of the NDIR technique. Complete analysis of variance was carried out to evaluate and compare the operational advantages of the proposed sensory structures. The experiments demonstrated the effect of the gold-coated walls in structured light source compartments with and without a parabolic reflector. Mixtures containing N2O, CH4, and CO2 were examined to determine the effect of interfering gases having absorption peaks similar to CO2 on the robustness of the proposed sensor. It was concluded that, although the use of a parabolic reflector concentrates rays on the detector area and increases its temperature, enhanced natural convection in the proposed sensor structure lowered the rate of temperature increase and the resulting thermal drift.

Characterization of a commercial lower-cost medium-precision non-dispersive infrared sensor for atmospheric CO<sub>2</sub> monitoring in urban areas

Abstract. CO2 emission estimates from urban areas can be obtained with a network of in situ instruments measuring atmospheric CO2 combined with high-resolution (inverse) transport modelling. Because the distribution of CO2 emissions is highly heterogeneous in space and variable in time in urban areas, gradients of atmospheric CO2 (here, dry air mole fractions) need to be measured by numerous instruments placed at multiple locations around and possibly within these urban areas. This calls for the development of lower-cost medium-precision sensors to allow a deployment at required densities. Medium precision is here set to be a random error (uncertainty) on hourly measurements of ±1 ppm or less, a precision requirement based on previous studies of network design in urban areas. Here we present tests of newly developed non-dispersive infrared (NDIR) sensors manufactured by Senseair AB performed in the laboratory and at actual field stations, the latter for CO2 dry air mole fractions in the Paris area. The lower-cost medium-precision sensors are shown to be sensitive to atmospheric pressure and temperature conditions. The sensors respond linearly to CO2 when measuring calibration tanks, but the regression slope between measured and assigned CO2 differs between individual sensors and changes with time. In addition to pressure and temperature variations, humidity impacts the measurement of CO2, with all of these factors resulting in systematic errors. In the field, an empirical calibration strategy is proposed based on parallel measurements with the lower-cost medium-precision sensors and a high-precision instrument cavity ring-down instrument for 6 months. The empirical calibration method consists of using a multivariable regression approach, based on predictors of air temperature, pressure and humidity. This error model shows good performances to explain the observed drifts of the lower-cost medium-precision sensors on timescales of up to 1–2 months when trained against 1–2 weeks of high-precision instrument time series. Residual errors are contained within the ±1 ppm target, showing the feasibility of using networks of HPP3 instruments for urban CO2 networks. Provided that they could be regularly calibrated against one anchor reference high-precision instrument these sensors could thus collect the CO2 (dry air) mole fraction data required as for top-down CO2 flux estimates.

Carbon Monoxide Sensor Based on Non-Dispersive Infrared Principle

Carbon monoxide (CO) is one of the toxic air pollution produced in incomplete combustion of carbon-containing fuels. At a certain threshold of concentration, this gas can harm the environments and affect the human health. Unfortunately, it cannot be detected by humans. In this study, CO gas detection has been designed and constructed using the principle of Non-Dispersive Infrared (NDIR). An incandescent light bulb is used to provide infrared source. An optical filter based on interferometry with a bandpass of about 4.63 μm is used to pass the light which corresponds to the CO gas absorption. The TPS 334 thermopile sensor is used to measure light intensity after gas absorption. The built-in RTD in the thermopile is involved to compensate the results of the gas concentration measurement. The experimental result shows that this NDIR sensor can measure CO gas concentration with a sensitivity of about 7 mV / ppm.

Self-Calibrated Multiharmonic CO2 Sensor Using VCSEL for Urban In Situ Measurement

Greenhouse gases have a significant impact on general global climate change. A self-calibrated multiharmonic measurement system based on tunable diode laser absorption spectroscopy (TDLAS) with wavelength modulation spectroscopy, using the vertical-cavity surface-emitting laser, is developed and applied to measure the CO2 and H2O concentrations in the urban areas. The precision of the developed system is evaluated using the Allan variance method, and it is found that the multiharmonic can enhance the precision of the system and the first-to-third harmonics are sufficient to achieve the lowest Allan deviation. To validate its accuracy, comparison experiments with the commercial nondispersive infrared (NDIR) instrument (Li-Cor 840A) are performed and the results demonstrate the high accuracy of the TDLAS system and its consistency with the NDIR instrument. Measurements were carried out in autumn and winter of 2017 in the city center of Munich. The results indicate that the in situ measurement of the CO2 concentration in the downtown area correlates with both natural and anthropogenic activities. Due to its high precision and accuracy, the self-calibrated multiharmonic measurement system has a great potential to further study the emission and distribution of CO2 in the urban areas.

Fast-response concentration measurement of bromotrifluoromethane using a quantum cascade laser (QCL) at 8280 μm

In this study, a measurement system for a gaseous fire extinguisher bromotrifluoromethane (Halon 1301) was developed, using a quantum cascade laser (QCL) at ~8.280 μm. The performance parameters of this system were also analyzed. Much higher sensitivity and faster response time were achieved compared to non-dispersive infrared (NDIR) sensors and differential-pressure method. A response time of 90 ms from 0% to the targeted concentration 6% was obtained. The detection limit of 500 ppm was obtained with a short optical path length of 2.8 mm. In conclusion, the proposed system can be applied in the airworthiness certification test of an aircraft fire suppression system.

Carbon dioxide measurement in Irish blanket peatlands: An assessment of pool-soil flux variability

Peatlands have been recognised as having a significant role in the mediation of atmospheric carbon dioxide (CO2) levels with direct implications for global climate change. Longitudinal in situ measurement systems for CO2 concentrations in blanket peatland ecosystems are difficult to implement where the nature of terrestrial–aquatic connectivity and hydrodynamics have a significant effect on the carbon cycle. The need for greater data on CO2 concentrations and flux monitoring in these settings has been well recognised. However, applying the most appropriate monitoring approach presents a special challenge. This paper sets out the development of a direct method for field based longitudinal CO2 concentration measurement. Based on experiential considerations a new approach is presented that addresses the complexity associated with the high diurnal dynamics of CO2 evasion during mid-winter in an Irish blanket peatland soil–water system. The paper outlines the significance of a direct in situ continuous measurement strategy using a non-dispersive infrared (NDIR) sensor to evaluate CO2 concentrations. The CO2 concentrations recorded as part of this study showed significant differences between the pond waters and the peat waters. The overall CO2 concentration trend did not correlate with the temperature patterns. Further monitoring is essential to evaluate the spatial and longitudinal trends in carbon dynamics. Outputs of this study will have a direct bearing on approaches to carbon flux determinations for this landscape type and will provide an important input to future efforts to explore carbon-hydrodynamics in the surface and sub-surface waters of blanket peatlands.

Long Term Stable Δ-Σ NDIR Technique Based on Temperature Compensation

For a fast and long term stable Non Dispersive Infrared (NDIR) technology of gas concentration measurement, the temperature compensation is required. A novel proposed Δ-Σ NDIR system was investigated and built with a closed-loop feedback system to stabilize the signal readings without temperature drift. The modulation of the infrared heater gives a corresponding signal of gas concentration based on our proposed Δ-Σ conversion algorithm that was affected by the drift of temperatures for the infrared sensor. For our study, a new temperature compensation model was built and verified that formulates the relationship between gas concentration and temperature of sensor. The results show that our proposed Δ-Σ can measure efficiently with half of the startup time than our previous design and maintain long term stability.

Effects of Isotopic Calibration Gases on IR Quantification Analyzer Techniques to Measure CO and CO <sub>2</sub> in Engine Emissions Testing

<div class="section abstract"><div class="htmlview paragraph">Infrared spectroscopic methods are the most common methods in the automotive industry for measuring carbon monoxide (CO) and carbon dioxide (CO<sub>2</sub>) gases. Concentrations of both gases, which are emitted from the combustion of fuels, are required to be determined accurately in order to follow strict environmental regulations. Appropriate analytical techniques and accurate calibration gas mixtures are therefore critical for successful measurements. Regulatory documents such as the EPA’s Code of Federal Regulations 40 (CFR 40) part 1065.250, UN ECE-R83, and (EU) 2017/1151 recommend a nondispersive infrared (NDIR) analyzer to measure CO and CO<sub>2</sub> concentrations in raw or diluted exhaust gas samples. Over the last decade, Fourier Transform Infrared (FTIR) spectrometry has been validated and recommended in engine exhaust certification testing as well as in engine and vehicle development activities.</div><div class="htmlview paragraph">The variation in the isotopic ratio of <sup>13</sup>C/<sup>12</sup>C in natural atmospheric CO<sub>2</sub> is in the range of ± 2‰ however, artificial or non-natural sources of CO or CO<sub>2</sub> can potentially have much larger variances. To fully understand the impacts of isotopic composition on the analyzers, the δ<sup>13</sup>C values used in this study were selected to cover a broad range of non-natural isotope ratios (very depleted and enriched). In the present work on both FTIRs and NDIRs, up to 4% deviation in analytical results were observed relative to the base case composition (-12‰ <sup>13</sup>CO) when the CO/N<sub>2</sub> gas mixture was enriched to 2630‰ with <sup>13</sup>C content. Analytical deviations measured on NDIR analyzers were more pronounced (4-14%) relative to the base case composition with the change of <sup>13</sup>C in the CO<sub>2</sub>/N<sub>2</sub> mixture from -982‰ to 6783‰. Moreover, the error with FTIR measurements could rise up to a factor of 2 or more depending on the <sup>13</sup>C and <sup>12</sup>C band selection and their evaluation methods. Known isotopic gas mixtures and careful evaluation band selection in the FTIR method were observed to reduce the analytical errors. Even though calibration gases were prepared accurately for molecular concentrations, carbon isotopic concentrations far removed from natural abundance showed significant errors in the measurements. It is therefore essential to have either known or natural ratios of carbon isotope calibration gas mixtures for accurate emission measurements.</div></div>

FireNose on Mobile Robot in Harsh Environments

In this work we present a novel multi-sensor unit, a.k.a. FireNose, to detect and discriminate both known and unknown gases in uncontrolled conditions to aid firefighters under harsh conditions. The unit includes three metal oxide (MOX) gas sensors with CMOS micro heaters, a plasmonic enhanced non-dispersive infrared (NDIR) sensor optimized for the detection of CO2, a commercial temperature humidity sensor, and a flow sensor. We developed custom film coatings for the MOX sensors (SnO2, WO3 and NiO) which greatly improved the gas sensitivity, response time and lifetime of the miniature devices. Our proposed system exhibits promising performance for gas sensing in harsh environments, in terms of power consumption (~ 35 mW at 350°C per MOX sensor), response time (< 10 s), robustness and physical size. The sensing unit was evaluated with plumes of gases in both, a laboratory setup on a gas testing rig and on-board a mobile robot operating indoors. These high sensitivity, high-bandwidth sensors, together with online unsupervised gas discrimination algorithms, are able to detect and generate their spatial distribution maps accordingly. In the robotic experiments, the resulting gas distribution maps corresponded well to the actual location of the sources. Therefore, we verified its ability to differentiate gases and generate gas maps in real-world experiments.

Open-path Halon 1301 NDIR sensor with temperature compensation

Halon 1301 (bromotrifluoromethane) is a kind of important fire extinguishing agent in aviation industry. Volume concentration measurement of Halon 1301 is necessary in the design of aircraft fire protection systems. In this research, an open-path Halon 1301 non-dispersive infrared (NDIR) sensor has been developed for in-situ measurement, a novel cavity-type absorption module was designed to get fast response and more compact structure. Experiment results show that measurement was remarkably affected by temperature. Therefore, temperature compensation algorithm was also studied in this thesis, which was proven to be effective within the range of 25–105 °C.

Optimised Performance of Non-Dispersive Infrared Gas Sensors Using Multilayer Thin Film Bandpass Filters

In this work, performance improvements are described for a low-power consumption non-dispersive infrared (NDIR) methane (CH4) gas sensor using customised optical thin film bandpass filters (BPFs) centered at 3300 nm. BPFs shape the spectral characteristics of the combined mid-infrared III–V based light emitting diode (LED)/photodiode (PD) light source/detector optopair, enhancing the NDIR CH4 sensor performance. The BPFs, deposited using a novel microwave plasma-assisted pulsed DC sputter deposition process, provide room temperature deposition directly onto the temperature-sensitive PD heterostructure. BPFs comprise germanium (Ge) and niobium pentoxide (Nb2O5) alternating high and low refractive index layers, respectively. Two different optical filter designs are progressed with BPF bandwidths (BWs) of 160 and 300 nm. A comparison of the modelled and measured NDIR sensor performance is described, highlighting the maximised signal-to-noise ratio (SNR) and the minimised cross-talk performance benefits. The BPF spectral stability for various environmental temperature and humidity conditions is demonstrated.

A Novel Bandpass Filter for the Analysis of Carbon Monoxide Using a Non-Dispersive Infrared Technique

In this study, two novel narrow bandpass filters (BPF) obtained from the high-resolution transmission molecular absorption (HITRAN) data for a carbon monoxide (CO) non-dispersive infrared (NDIR) analyzer were investigated and compared with a commercial BPF (4.64 µm). The new BPF was made using a two-cavity filter method with different center wavelengths and bandwidths from the commercial BPF. The wavelengths of the two BPFs were 4.5 µm and 4.65 µm. The gas emission pattern of a coal-fired power plant was used as a case study. Various concentrations of target gases were used to theoretically estimate the interference, and to practically determine it. It was found that although the transmittances of the two new BPFs were lower than that of the commercial BPF, the signal-to-noise ratio caused by two novel BPFs was approximately 20. In terms of interference effect, carbon dioxide (CO2) was found as a strong interfering gas on the commercial BPF at 4.64 µm and the new BPF at 4.65 µm. In contrast, the new BPF at 4.5 µm cut off the interference effect of all target gases. The measurement error of the NDIR analyzer applying the BPF at 4.5 µm was similar to that of gas filter correlation (GFC) NDIR and was less than 1%. This indicates that the novel BPF at 4.5 µm can be used instead of a GFC for a CO NDIR analyzer, thus overcoming the limitations of using a GFC.

Ultra-narrowband Emitters/Absorbers Based on Metal–Insulator–Metal Stacks for Nondispersive Infrared Gas Sensors

Ultra-narrowband Emitters/Absorbers Based on Metal–Insulator–Metal Stacks for Nondispersive Infrared Gas Sensors

Investigation of the response of high-bandwidth MOX sensors to gas plumes for application on a mobile robot in hazardous environments

A custom sensor module has been developed comprising high-bandwidth metal oxide (MOX), low-cost non-dispersive infra-red (NDIR) and miniature solidly mounted resonator (SMR) acoustic sensors for use on a mobile exploration robot. The module has been tested in a wind tunnel in order to evaluate the performance of three MOX sensors (with coatings of PdPt SnO2, WO3 and NiO) to plumes of 2-propanol (concentration < 2.5 ppm). The formation of the VOC (volatile organic compound) plumes was verified through mapping of sensor responses across a grid of 9 positions in the wind tunnel. Fluctuating sensor responses were observed (±5%), demonstrating variation of VOC concentration within the gas plumes. Higher sensor responses were demonstrated with the n-type SnO2 and WO3 based devices (80% and 40% change relative to baseline, respectively) compared to the p-type NiO device (10%). Short plumes of VOC demonstrated the effect of gas pulse broadening, where longer duration responses (10% greater) were observed at locations further from the VOC source (∼0.4 m distance variation tested). Finally, the module was tested in a real-world environment, where plumes of VOC were observed using the MOX sensors and verified using a commercial Photoionization Detector (PID).

Characteristics and Temperature Compensation of Non-Dispersive Infrared (NDIR) Alcohol Gas Sensors According to Incident Light Intensity.

This paper discusses the output characteristics of the sensor response of infrared ethanol gas detectors based on incident radiation intensity. Sensors placed at each focal point of two elliptical waveguides were fabricated to yield two module combinations and to verify the output characteristics. A thin Parylene-C film was deposited onto the reflector surfaces of one module. The thermal properties were compared between the sensor (2.0 Ø) and sensor with a hollow disk (1.6 Ø), the disk being mounted at the end of one detector. The fabricated sensor modules were placed inside a gas chamber. The temperature was increased from 253 K to 333 K, over the concentration range from 0 to 500 ppm. As the temperature increases by 10 K, the output of sensor (2.0 Ø) without and with Parylene-C coating typically increased by 70 mV and 52 mV, respectively. However, the sensor output with the hollow disk showed an average decrement of 0.8 mV/50 ppm and 1 mV/50 ppm for module without and with Parylene-C deposition, respectively. For concentrations higher than 50 ppm, the estimation error was around ±5%. Further, the sensitivity to temperature variation and the absorbance of infrared (IR) reflection was found higher for Parylene-C coated module.

Comparison of a laser methane detector with the GreenFeed and two breath analysers for on-farm measurements of methane emissions from dairy cows

To measure methane (CH4) emissions from cattle on-farm, a number of methods have been developed. Combining measurements made with different methods in one data set could lead to an increased power of further analyses. Before combining the measurements, their agreement must be evaluated. We analysed data obtained with a handheld laser methane detector (LMD) and the GreenFeed system (GF), as well as data obtained with LMD and Fourier Transformed Infrared (FTIR) and Non-dispersive Infrared (NDIR) breath analysers (sniffers) installed in the feed bin of automatic milking systems. These devices record short-term breath CH4 concentrations from cows and make it possible to estimate daily CH4 production in g/d which is used for national CH4 emission inventories and genetic studies. The CH4 is released by cows during eructation and breathing events, resulting in peaks of CH4 concentrations during a measurement which represent the respiratory cycle. For LMD, the average CH4 concentration of all peaks during the measurement (P_MEAN in ppm × meter) was compared with the average daily CH4 production (g/d) measured by GF on 11 cows. The comparison showed a low concordance correlation coefficient (CCC; 0.02) and coefficient of individual agreement (CIA; 0.06) between the methods. The repeated measures correlation (rp) of LMD and GF, which can be seen as a proxy for the genetic correlation, was, however, relatively strong (0.66). Next, based on GF, a prediction equation for estimating CH4 in g/d (LMD_cal) using LMD measurements was developed. LMD_cal showed an improved agreement with GF (CCC = 0.22, CIA = 0.99, rp = 0.74). This prediction equation was used to compare repeated LMD measurements (LMD_val in g/d) with CH4 (g/d) measured with FTIR (n = 34 cows; Data Set A) or NDIR (n = 39 cows; Data Set B) sniffer. A low CCC (A: 0.28; B: 0.17), high CIA (A: 0.91; B: 0.87) and strong rp (A: 0.57; B: 0.60) indicated that there was some agreement and a minimal re-ranking of the cows between sniffer and LMD. Possible sources of disagreement were cow activity (LMD: standing idle; sniffer: eating and being milked) and the larger influence of wind speed on LMD measurement. The LMD measurement was less repeatable (0.14–0.27) than the other techniques studied (0.47–0.77). Nevertheless, GF, LMD and the sniffers ranked the cows similarly. The LMD, due to its portability and flexibility, could be used to study CH4 emissions on herd or group level, as a validation tool, or to strengthen estimates of genetic relationships between small-scale research populations.

Carbon dioxide determination in atmosphere by non dispersive infrared spectroscopy: A possible approach towards the comparability with seawater CO2 measurement results

The rising levels of carbon dioxide in the atmosphere are responsible for fundamental changes occurring in seawater carbonate chemistry. The partial pressure of oceanic CO2 (pCO2) is one of the four measurable parameters defining the marine carbon system. For this reason, the pressing need of assuring metrological traceability of pCO2 measurement results has been recognized and pointed out by the oceanographic community. In order to achieve this fundamental goal, the lack of suitable reference materials has been identified as one of the most limiting factors. At INRIM several activities are carried out to establish the metrological traceability for carbon dioxide measurement results. The present paper describes two primary methods, the gravimetry and the dynamic dilution, used for the preparation of gaseous reference standards for composition which are fundamental to calibrate sensors and analytical instrumentation for carbon dioxide determination in atmosphere. Suitable procedures for the calibration and use of Non Dispersive Infrared Analysers (NDIR) are also presented and discussed. At present, feasibility studies are ongoing at INRIM to extend the use of these metrologically traceable mixtures to the calibration of sensors used for pCO2 determination in seawater. An extensive work was carried out on a non-dispersive infrared analyser employed in air monitoring, to assess its robustness and stability, which are the major starting points to set up a calibration procedure to obtain comparable results in the atmospheric and marine compartments.

Anaerobic digestion and agricultural application of organic wastes

The anaerobically digestion and agricultural application of organic wastes was conducted using food wastes and cow dung. Twenty kilograms each of the feed stocks was added into two 30 liters-capacity batch digesters. The anaerobic digestion was carried out within a temperature range of 25 – 31O C for a retention time of 51days. The results showed a cumulative gas yield of 5.0 bars for food waste and no gas production for cow dung within the retention time. Bacteria such as Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Proteus vulgaris and Clostridium sp were isolated. Fungi isolated included Aspergillus niger, Aspergillus nidulan, Trichophyton rubrum and Epidermophyton flocossum. The non-dispersive infrared (NDIR) analysis of the biogas produced confirmed that the gas consisted of CH4, CO2 and H2. Statistical analysis revealed there was no significant correlation between temperature and biogas produced from the organic wastes (r= 0.177, p = 0.483).The organic wastes from the biogas production process stimulated maize growth when compared to control (soil without organic waste) and indicated maximum height. The study therefore reveals that food waste as potential substrates for biogas production has a moderate bio-fertilizer potential for improving plant growth and yield when added to soil.

Simulating the potential for Carbon Dioxide (CO2) reduction by the application of environmentally friendly transportation (case study: Gatot Subroto Street, Medan City)

Carbon Dioxide (CO2) is one of the greenhouse gases. One source of greenhouse gases comes from the use of fossil fuels from the transport sector. The transportation sector is one of the dominant sectors in contributing to the greenhouse effect. This study aims to calculate the amount of CO2 from transportation activities by using mobile six equations in Gatot Subroto Street, Medan City. A sampling of CO2 concentration was done using Carbon Dioxide Monitor with Non-Dispersive Infra Red (NDIR) Analyzer method. Also, a simulation of the reduction of the number of private vehicles to mass transportation such as BRT gas-fired. The results showed CO2 emissions calculations with mobile six ranged from 47.2 kg CO2 - 978.2 kg CO2. Meanwhile, measurements range from 3,004 ppm - 3,405 ppm. Implementation of the concept of environmentally friendly transportation such as BRT in Gatot Subroto Street, Medan City will be able to reduce the average emissions load CO2 by 42.75% -78.80%. Based on the calculation simulation in this study is estimated the number of BRT required approximately 71 units.