Precision Measurements in Air Quality & Turbulence Incubator: Day 1
George Nehmetallah
Precision Measurements in Air Quality & Turbulence Incubator: Day 1
Dr. Quarles started off the day by celebrating OSA’s 100th anniversary and highlighting the UN sustainable development goals till 2030, especially for pollution monitoring and future challenges and opportunities. Host Dr. Banerjee stated the motivation behind this gathering is to mitigate the pollution effects which is affecting more than 1 billion people and causing up to 1 million premature deaths and 1 million pre-native deaths each year.
The first “big picture” talk was by Dr. M. Vorontsov, from the University of Dayton. His talk emphasized on the relation between fluid dynamics, statistical wave optics and atmospheric turbulence mitigation using adaptive optics. He also emphasized on the need of eye safety from lasers due to spikes of intensity due to turbulence. This was followed by Dr. J. Whetstone’s (from NIST) big picture talk on the importance of developing integrated greenhouse gas (GHG) flux measurement systems and optical remote sensing using ground-based, airborne, and space based sensors which are essential in the effort for detection and modeling of the air quality. He also talked about NIST’s GHG and climate science measurement program which focuses on increasing accuracy (spatial and temporal) of continuous emission monitoring technology and achieve the level of measurement capability and enhance sensor precision to drive and enforce regulations.
The third big picture talk was given by Dr. R. Chen who discussed his work on semiconductor membrane based integrated photonic sensors for air and water pollution sensing. These novel slotted photonic crystal waveguides offer a unique platform for lab-on-chip absorption spectroscopy via slow light enhanced path length to substitute current FTIR technology. These novel sensors are low cost, adaptable, small, high sensitivity, high throughput, and will be instrumental for early warning the population in case of a chemical warfare and early cancer detection.
The post-lunch sessions comprised two panel discussions that included short talks followed group discussions. The first talk was by Fred Mashary, from CCNY, on regional impact of wild fires and the use of LIDAR for aloft plumes observation and particle classification. He also discussed how remote sensing to trace gases and aerosols in the urban environment and showed how absorption and extinction Angstrom exponents are used in the clustering and classification of these plumes. Anna Karion from NIST discussed in-situ GHG measurements of CO2/CO/CH4,O3, etc..) using global networks as well as airborne measurements techniques. She emphasized on the importance of compatibility of these measurements and those obtained through LIDAR. Chris Hovde from Southwest Sciences, Inc. discussed the industrial techniques developed for gas detection (natural gas, water vapor, methane, and CO2) based on tunable diode laser technology. He showed that high sensitivity is achieved by wavelength modulation and long optical path length. He also briefly discussed the detection of formaldehyde detectors to be used with astronauts and the detection of TB and pneumonia by laser isotope spectroscopy. He concluded his talk on how laser based sensors serve broad commercial market. The last talk of this session was by Florian Adler, from Tiger Optics, where they developed commercial ring-down spectroscopy. He also emphasized on the advantages of such a technique in terms of high sensitivity. High resolution, cost saving, and user friendly. Also, he acknowledged some challenges in terms of robustness, and consistency. He also discussed some applications in the coal industry to measure HCl, CO2, and SO2 pollutants. In the ensuing panel discussion, the relation between instrument calibration and the accuracy needed in a particular measurement was debated. There was also a discussion on the effect of temperature and pressure, which affect the backscattering coefficient, on the LIDAR measurements. The session ended with a debate about how the high cost of the instruments used is keeping them from being commercially available so far.
In the second panel, Gerard Wysocki from Princeton University presented a revolutionary idea in terms of using phase rather than absorption for spectroscopy. He discussed the various issues while using absorption technique. Instead, he suggested to use chirped laser dispersion spectroscopy and mimic the advantages of QPSK and FM modulation techniques over AM modulation. The advantages are large dynamic range, linear response immunity to amplitude noise and power variation, insensitivity to detector nonlinearity, fast measurement. Next, Mark Phillips from Pacific Northwest National laboratory talked about broadband spectrum and sensing using swept external cavity quantum cascade laser (QCL). This technique is capable of multi-chemical detection and large molecule detection. The advantages of such a system is high resolution, broadband, and real time IR spectroscopy and sensing. High scan repeatability and stability allow averaging to improve sensitivity. Barry McManus from Aerodyne Research, Inc. talked about high precision trace gas instruments for atmospheric chemistry. The technology developed by his company can measure combination of trace gases using MIR-CW-QCL systems using direct absorption spectroscopy. The last talk in this session was by Ian Coddington from NIST who introduced Dual Comb spectroscopy in the open air. This uses a broadband coherent light source and uses standard heterodyne detection. The advantages of this system are high resolution, ultra-high frequency accuracy, high noise suppression, fast, and background subtraction. However, the main weakness is dynamic range limit, and time resolution to study turbulence. After that there was a panel discussion about how to mitigate the cost issues. The panel agreed that although in the last decade the price and size of equipment has been reduced and precision has been improved (almost 0.1ppm) still there is some hurdles to overcome. Finally, James Whetstone suggested that maybe the broadband technology might be the future link between air quality community and the greenhouse gases community.
More to come from the Precision Measurements in Air Quality & Turbulence, Day2. Stay Tuned!
George Nehmetallah, Cathlolic University of America
