Several environmental trace gas species and toxic chemicals or warfare simulants have fingerprint spectral signatures in the mid-infrared region of the spectrum. For instance, methane, nitrous oxide, and water vapor are critical greenhouse gases relevant for environmental sensing. In contrast, Sarin is one of the most lethal warfare agents that is a highly toxic synthetic chemical organophosphorus compound, which is of interest in defense and security sensing applications. Due to complex chemical structure and significant absorption and collision cross-section, the molecular linewidths of such chemicals can cover a broad range of spectral widths in the mid-infrared region. Detection of such molecules in the mid-infrared region is sensitive, which requires broadly tunable sources and appropriate spectral resolution in detection schemes. We show a rapid detection methodology of atmospheric bands of trace gases in the 7 μm to 8 μm region, which also coincides with the fingerprints region of several hazardous chemicals. Methane absorbs strongly in the wavelength range of 3 μm to 8 μm, and nitrous oxide has absorption from 5 μm to 8 μm. We use molecular rotational-vibrational transitions of carbon and nitrogen trace species to demonstrate well-resolved peaks in the spectral region of 6.88 μm to 7.6 μm for detection. The detection was performed by a continuous wave multiplexed quantum cascade laser source capable of an ultra-wide tuning range from 6.88 μm to 11.05 μm.
KEYWORDS: Absorption, Mid-IR, Methane, Sensors, Spectroscopy, Quantum cascade lasers, Chemical weapons, Signal detection, Nitrous oxide, Biological and chemical sensing
Several chemical warfare chemicals have fingerprint spectral signatures in the mid-infrared region of the spectrum. For instance, Sarin is one of the most lethal warfare agents that is a highly toxic synthetic chemical organophos phorus compound. Due to complex chemical structure and large absorption and collision cross-section, the molecular linewidths of such chemicals can cover a broad range of spectral width. Detection of such molecules in the mid-infrared region is sensitive which requires broadly tunable sources and detection methods. We show a rapid detection methodology of such chemicals using proxy methane and nitrous oxide atmospheric bands in the 7 µm to 8 µm region which also have fingerprints region of several hazardous chemicals. Methane absorbs strongly in the wavelength range of 3 µm to 8 µm, nitrous oxide has absorption from 5 µm to 8 µm. As the large wavelength range that they have covered, we use molecular rotational-vibrational transitions of CH4
It is estimated that about 60 percent of total global methane emissions are thought to be from anthropogenic sources and about 40 percent from natural sources. Anthropogenic sources encompass a wide range of human activities, including food and energy production and waste disposal. Livestock (through fermentation processes in their digestive system that generates methane and manure management), rice cultivation, landfills, and sewage account for 55-57 percent of global anthropogenic emissions. This paper investigates methane emissions from agricultural land-use and livestock (e.g., poultry and cattle) farming practices in Delaware. Laser-based point sensing can provide a higher spatial and temporal resolution that can complement satellite observations to identify individual sources and broader geographical areas. A detailed understanding of their sources and sinks is necessary to model emissions profile accurately. This paper shows field measurements of methane using mid-IR laser-based sensors and validation with satellite data. We conducted our field deployment locally in the Delaware, Kent, and Sussex county regions focusing on high methane emitting areas. We used the TROPOspheric Monitoring Instrument (TROPOMI) methane satellite data to get a unified emissions map of methane production in Delaware by comparing our ground-based measurements with the satellite data. Furthermore, we examined the satellite data for long-term methane emissions trends to quantify 2020 average methane emissions.
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