OPS
Identify and Quantify Gas Compounds in Open Path and in Real-Time
OPS is an active remote sensing system based on Fourier-transform Infrared (FT-IR) spectroscopy which can accurately quantify gas compounds even at low concentrations, i.e., in the ppb range.
Typical applications of the OPS include fenceline monitoring, i.e., the quantification of gas compounds along the property boundary of an industrial site, like refinery or chemical plant. It is also often used for emission monitoring, e.g., of fugitive gases, exhaust gases, agricultural gases, and wildfire emissions. Please see also the last section below for selected publications on various applications of the OPS.
The working principle of OPS is:
Infrared radiation from the internal mid-infrared (MIR) light source is modulated by an interferometer and transmitted through a telescope to a retroreflector array which is typically positioned several hundred meters away from the spectrometer. The reflected radiation is received by the same telescope and focused onto a detector.
All IR-active gas compounds between the spectrometer and retroreflector array absorb this MIR radiation inducing characteristic absorption features in the measured IR spectrum. OPS identifies these gases and quantifies their average concentrations in real-time based on the analysis of the infrared signatures in the resulting absorption spectrum.
Calibration-Free Quantification
OPS is operated by the remote sensing software OPUS RS/OPS. Similar to our Gas Analysis software OPUS GA for our benchtop multi-gas analyzers, OPUS RS/OPS enables the quantification of multiple gases without the need for calibration to the target gases. The quantification is based on a unique non-linear fitting algorithm which fits a reference spectrum of the target compound to the measured spectrum. Interfering gases in the atmosphere are considered in the fitting procedure.
The temporal behavior of the methanol concentration (upper window, red datapoints) quantified by OPS along the beam path clearly shows values fluctuating from 60 to 120 ppb.
The measured spectrum corresponding to each datapoint of the timeseries above can also be investigated in detail. The lower window shows the measured spectrum (black) in the spectral range where methanol is quantified. This spectrum is already automatically corrected by the baseline and the absorptions of interfering compounds. The reference spectrum of methanol (red) agreed well with the measured one. Here, the spectrum from the measurement at 63 s is shown.
Easy Creation of New References
Adding new references to the library of compounds which are quantified in real-time during the measurement just takes a few clicks in OPUS RS/OPS software. The user only needs to select these compounds from the available quantitative gas library (including more than 350 compounds) and set up a few parameters to create the reference. Existing measurements can be re-analyzed with the newly added references at any time without rerunning the measurement.
High Resolution and Fast Analysis
OPS has a superior spectral resolution of 1.0 cm-1, which can optionally be upgraded to 0.5 cm-1. This high spectral resolution facilitates the analysis of complex gas mixtures characterized by numerous overlapping infrared signatures. Furthermore, the high measurement rate of up to 5 Hz at a resolution of 0.5 cm-1 enables the investigation of gas compositions in the open path in real-time, even if they are rapidly changing.
Automated Positioning for Covering Multiple Directions
When monitoring of multiple directions is required, Bruker offers the motorized pan-tilt head which can be precisely controlled and programmed in OPUS RS/OPS to point the spectrometer in different directions where individual retroreflector arrays are installed.
OPS Applications (selected publications)
Quantifying the Impact of the COVID-19 Pandemic Restrictions on CO, CO2, and CH4 in Downtown Toronto Using Open-Path Fourier Transform Spectroscopy. Atmosphere (2021)
Beef cattle methane emissions measured with tracer-ratio and inverse dispersion modelling techniques. Atmospheric Measurement Techniques (2021)
Quantifying fugitive gas emissions from an oil sands tailings pond with open-path Fourier transform infrared measurements. Atmospheric Measurement Techniques (2021)
Air quality impacts of smoke from hazard reduction burns and domestic wood heating in western Sydney. Atmosphere (2019)
Vehicle ammonia emissions measured in an urban environment in Sydney, Australia, using open path fourier transform infrared spectroscopy. Atmosphere (2019)
Characterization of trace gas emissions at an intermediate port. Atmospheric Chemistry and Physics (2018)
Long-path measurements of pollutants and micrometeorology over Highway 401 in Toronto. Atmospheric Chemistry and Physics (2017)
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