Sonya Pyo, Paulo Castillo, Ihor Sydoryk, Barry Gross, Fred Moshary Optical Remote Sensing Lab City College of New York, New York, NY 10031
To develop methods to measure ambient gases of interest, utilizing the relatively strong absorption features in the MIR is extremely efficient. While active QCL technologies are being considered, they must ultimately be validated as far as possible with existing technologies. For this reason, we explore the potential of Open Path Fourier Transform Infrared Spectroscopy (FTIR) to see ambient concentrations of relevant trace gases. Although trace gases make up less than 1% of the atmosphere, they can affect air quality as well as act as important greenhouse gases that can have significant impact on climate change. Accurately retrieving the concentration of such gases is the first step in the effort of finding the sources of these gases and thereby curb human's contribution to air pollution. At the same time, they can set a standard for future QCL systems. In our experimental arrangement, a broadband thermal IR radiation source (2-16um) is directed to a suitable LN2 cooled Detector over a path length of 300 m. In going to the detector, the radiation passes through the atmosphere and is collected by a Newtonian telescope. The telescope collects the light, collimates it and directs it to the detector, through the Michelson interferometer, where the final signal is read, an interferogram is generated and the power spectra obtained using fourier transform methods. In optimizing the retrievals, we make use of suitably selected microwindows suitable for small number of gases. A Least Square Analysis of the microwindow spectrum is used and based on fitting the measured spectra to theoretical reference spectra generated from Genspect, a Matlab program. In this presentation, we make measuremtns during the heatwave of July 21, 2011 and compare the trace gas concentrations for H20, CO, CH4 and O3 against ground samplers. These measurements form a baseline in which to assess future QCL development.