The Fluid Metrology Group leads the world in designing and using gas-filled acoustic resonators for measuring the thermodynamic temperature T, the Boltzmann constant kB, and the thermophysical properties (e.g. heat capacity, shear viscosity, acoustic and density virial coefficients) of semiconductor process gases and environmentally benign heat transfer fluids (e.g. refrigerants). Now, we are using our expertise to solve problems related to greenhouse gases and climate change.
In collaboration with NIST’s Chemical Sciences Division, we use photoacoustic resonators
for continuous monitoring of the CO2 concentration in ambient air from a tall building rooftop; (see Fig. 2) 
for measuring the optical properties of particles (e.g. soot) in air that affect the energy balance of the earth; 
to develop a hybrid cavity-ringdown/photoacoustic spectrometer for measuring the abundance of C-14 in samples of CO2 to verify product origin.
In collaboration with China’s National Institute of Metrology, we use cylindrical acoustic resonators to re-determine the Boltzmann constant with fractional uncertainty of 3×10−6 from measurements of the speed of sound in argon. 
Design a Long-Wavelength Acoustic Flow Meter to measure the flux of carbon dioxide in the stack of a coal-burning power plant to facilitate a carbon tax or cap-and-trade regulations. Link to LWAF
Measured the thermodynamic temperature using cavities acting as simultaneous acoustic and microwave resonators from