Demonstration of an ethane spectrometer for methane source identification.

Methane is an important greenhouse gas and tropospheric ozone precursor. Simultaneous observation of ethane with methane can help identify specific methane source types. Aerodyne Ethane-Mini spectrometers, employing recently available mid-infrared distributed feedback tunable diode lasers (DFB-TDL), provide 1 s ethane measurements with sub-ppb precision. In this work, an Ethane-Mini spectrometer has been integrated into two mobile sampling platforms, a ground vehicle and a small airplane, and used to measure ethane/methane enhancement ratios downwind of methane sources. Methane emissions with precisely known sources are shown to have ethane/methane enhancement ratios that differ greatly depending on the source type. Large differences between biogenic and thermogenic sources are observed. Variation within thermogenic sources are detected and tabulated. Methane emitters are classified by their expected ethane content. Categories include the following: biogenic (<0.2%), dry gas (1-6%), wet gas (>6%), pipeline grade natural gas (<15%), and processed natural gas liquids (>30%). Regional scale observations in the Dallas/Fort Worth area of Texas show two distinct ethane/methane enhancement ratios bridged by a transitional region. These results demonstrate the usefulness of continuous and fast ethane measurements in experimental studies of methane emissions, particularly in the oil and natural gas sector.

Quartz enhanced photoacoustic spectroscopy with a 3.38 µm antimonide distributed feedback laser.

A system for gas sensing based on the quartz-enhanced photoacoustic spectroscopy technique has been developed. It makes use of a quantum well distributed feedback (DFB) laser diode emitting at 3.38 µm. This laser emits near room temperature in the continuous wave regime. A spectrophone, consisting of a quartz tuning fork and two steel microresonators were used. Second derivative wavelength modulation detection is used to perform low concentration measurements. The sensitivity and the linearity of the Quartz enhanced photoacoustic spectroscopy (QEPAS) sensor were studied. A normalized noise equivalent absorption coefficient of 4.06×10(-9) cm(-1)·W/Hz(1/2) was achieved.

Sensing of formaldehyde using a distributed feedback interband cascade laser emitting around 3493 nm.

We have demonstrated sensing of formaldehyde (H(2)CO) using a room-temperature distributed feedback interband cascade laser (ICL) emitting around 3493 nm. The ICL has been characterized and proved to be very suitable for tunable laser spectroscopy (TLS). The H(2)CO TLS spectra were recorded in direct absorption mode and showed excellent agreement with the Pacific Northwest National Laboratory database. The measurements reported here were taken from a series of measurements of a mixture of H(2)CO in air obtained by vaporizing a solution also containing methanol and formic acid. We obtained a resolution limit better than 1 ppm × m assuming a relative absorption of 10(-3).