Open Path FTIR Transmission Quantification With Temperature Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Open Path Fourier Transform Infrared (OP-FTIR) spectroscopy faces challenges in determining the physical location and magnitude of maximum pollutant concentration along a beam path due to its inability to control environmental factors like temperature and relative humidity, leading to inaccuracies in gas concentration measurements.
Innovation Solution
A method is developed to automatically determine the actual concentration of gases using optically derived analytical spectra and transmittance reference data, involving steps such as dividing the analytical spectrum by transmittance spectra for different gas concentrations, separating residual spectra, smoothing them, and identifying the concentration that minimizes the difference between absorbing and non-absorbing residual spectra.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If open path FTIR spectroscopy is used for remote sensing air monitoring, then the transportability and flexibility of the measurement system are improved, but the ability to control environmental factors like temperature and relative humidity deteriorates, leading to inaccuracies in gas concentration measurements
Solution Approach 1:
The patent applies parameter changes by using temperature-dependent transmittance reference spectra to compensate for environmental variations. The system selects and applies reference spectra corresponding to different temperature conditions to correct the analytical spectrum, thereby maintaining measurement accuracy despite uncontrolled temperature changes in the open path environment.
2Area of stationary object
If open path FTIR spectroscopy is used for remote sensing, then the sampling volume covers hundreds of meters and simultaneous monitoring of multiple compounds is improved, but the ability to obtain a background spectrum free of analyte interference deteriorates
Solution Approach 1:
The patent extracts the temperature information from the analytical spectrum itself by analyzing the shape and features of water vapor absorption lines. This extracted temperature parameter is then used to select appropriate transmittance reference spectra, effectively separating the temperature effect from the analyte concentration information and enabling accurate quantification without a pure background spectrum.
3Device complexity
If traditional FTIR quantification methods are used with uncontrolled environmental conditions, then the device complexity is kept simple, but the measurement precision deteriorates due to temperature and humidity variations affecting spectral features
Solution Approach 1:
The system performs self-service by automatically determining the temperature along the beam path directly from the analytical spectrum features, without requiring external temperature sensors or manual intervention. The microprocessor automatically selects the appropriate transmittance reference spectra based on the determined temperature and calculates the analyte concentrations, making the system self-correcting for environmental variations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves the accuracy of gas concentration measurements by effectively accounting for environmental and instrumental factors, reducing noise and interference, and enabling precise quantification of gases like water vapor and other target compounds.
Implementation Method 1
FTIR spectroscopes have been used for the evaluation of solid, liquid, and gas analytes since that time. The concept of a background spectrum is central to spectroscopy. In the simplest terms, Beer's law relates the amount of a substance present in an analytical sample to the amount of light absorbed by the analytical beam.
Data Source
AI summary
A transmission quantification approach that is effective at quantifying the concentration of key atmospheric gases, including water vapor and methane, does not require a background spectrum and is immune to changes between background and absorbance spectra. By using local minima and maxima in transmission of a target gas, this approach creates two spectral arrays as long as a single beam input spectra. One of these spectral arrays represents the points in wave-number space that are less absorbing points, and the other represents the more absorbing points. A concentration for a given gas is calculated by determining what reference concentration creates a residual after division by a pure gas spectrum that forces these two arrays to converge.