Development of a fluorescence lidar for measurement of atmospheric formaldehyde

In this paper, we describe the development of a prototype differential absorption fluorescence lidar for nighttime tropospheric formaldehyde (H2CO) concentration profiling. H2CO has a strong absorption band in the 352-357nm region and fluoresces strongly in the 390-500nm region. Here, we obtain high sensitivity (∼0.1ppb) measurements of H2CO profiles from differential fluorescence signals obtained by injection seeding a Nd:YVO laser and tuning its wavelength on and off the peak of a strong absorption line. The fluorescence signal strength is further improved by using a multi-line bandpass filter whose pass-bands are aligned to multiple fluorescence peaks of H2CO. A H2CO filled photo-acoustic absorption cell is utilized for tuning the seed laser wavelength to the center of absorption line.