The ALTAiR group develops and employs new and advanced optical technologies, including infrared spectroscopic instruments for trace gas detection and carbon isotope measurements, as well as advanced algorithms for the next generation of ground-based and airborne atmospheric measurements. A major focus is the development of ever more sensitive, selective, lighter, and autonomous instruments.
In 2006, we developed and successfully deployed the world’s first infrared absorption spectrometer employing non-linear optical mixing, known as difference frequency generation (DFG), on airborne platforms for ultrasensitive measurements of the trace gas formaldehyde. Using this and older technologies, ALTAiR group members have acquired measurements of this important ozone and hydrogen radical precursor from the arctic boundary layer, to lower and upper atmospheric regions of China, Japan, remote Pacific and Atlantic Oceans, Alaska, and various locations over the United States, Canada, and Mexico.
Working in close collaboration with atmospheric modelers, the ALTAiR group further analyze their high quality data thus acquired to advance the understanding of atmospheric hydrocarbon oxidation processes, chemical transformations, and ozone production rates throughout the troposphere and lower stratosphere.
In 2012, the ALTAiR group developed a new lighter and even more sensitive DFG spectrometer for the NCAR/NSF Gulfstream-V aircraft to study formaldehyde transported from low altitudes to the upper troposphere and lower stratosphere (UT/LS) during the 2012 Deep Convective Clouds and Chemistry (DC3) Study. Such transport affects hydrogen radicals and ozone formation in the UT/LS.
The ALTAiR group also deployed their older DFG instrument on the NASA DC-8 aircraft during the DC3 study.
A publication describing the new DFG infrared absorption spectrometer (Compact Atmospheric Multispecies Spectrometer, CAMS) on the GV aircraft and new multipass sampling cell is forthcoming.
The ALTAiR group deployed their older DFG instrument during the 2009 Ocean-Atmosphere-Sea Ice-Snowpack (OASIS) Study to measure formaldehyde fluxes from the arctic snowpack. During the arctic spring, boundary layer ozone is often completely or mostly depleted by reactions involving chlorine and bromine compounds. As formaldehyde is intimately involved in these reactions, quantifying formaldehyde snow emissions is important for a comprehensive understanding of the chemical processes involved. The gradient flux method, using sonic anemometers on two sampling towers, was employed.
Arising from the extreme flexibility of room-temperature mid-infrared DFG laser sources, where many atmospheric gases exhibit strong absorptions, and the flexibility of the nonlinear optical mixing approach many other trace atmospheric gases can be detected with the ALTAiR instruments. In fact, the CAMS instrument is being upgraded for simultaneous fast measurements of formaldehyde with ethane, the most abundant nonmethane hydrocarbon in the atmosphere and the second most abundant constituent of natural gas. Other trace gases are also under consideration for study.
In addition to more than 120 journal publications discussing their results and new instrument developments, the ALTAiR group published a book chapter detailing both theoretical and practical aspects of infrared absorption measurements.