Accuracy of Lidar Measurements of the Concentration of Hydrofluoride Molecules in the Atmospheric Boundary Layer
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OPTOPHYSICAL MEASUREMENTS ACCURACY OF LIDAR MEASUREMENTS OF THE CONCENTRATION OF HYDROFLUORIDE MOLECULES IN THE ATMOSPHERIC BOUNDARY LAYER V. E. Privalov1 and V. G. Shemanin2
UDC 551.510
Issues of atmospheric pollution by hydrofluoride molecules are brought to light. The use of a Raman lidar for remote measurement of the concentration of molecules of various pollutants at level of tens and hundred of units of the maximum permissible concentration is considered. The measurement error is estimated for the concentration on the order of 1014 cm–3 and greater by hydrofluoride molecules in synchronous photon counting mode by lidar of the Raman scattering of light in the atmospheric boundary layer of altitude up to 1.5 km. Results are presented of the numerical solution of the lidar equation for Raman scattering of light by hydrofluoride molecules: the possible measured concentration of hydrofluoride molecules is approximately 1.5·1014 cm–3 with relative measurement error less than 25% at the wavelength of 405 nm for investigatory altitude no greater than 500 m. Keywords: Raman lidar, concentration, hydrofluoride molecules, synchronous photon counting mode, atmospheric boundary layer.
Introduction. Contamination of atmospheric air by molecules of HF hydrofluoride presents a great problem in connection with its high toxicity and low level of maximum permissible concentrations (MPC): 0.02 mg/m3 in compliance with the hygienic standards of GN 2.1.6.3492-17 (as amended on May 31, 2018) “maximum permissible concentrations (MPC) of pollutants in atmospheric air of residential and agricultural locations” or approximately 1.5·1014 cm–3 [1, 2]. The development of new distant methods of measuring the required concentration of molecules of HF in the atmospheric boundary layer based on Raman lidar requires an estimate of the precision of the solution of such measurement problem. According to the theoretical analysis of methods of laser sounding of molecules of hydrocarbons in the aerosphere, it has been established that Raman lidar can be used for remote measurement of the concentration of molecules at a level of tens and hundreds of units of the maximum permissible concentration. The authors of this article present the lidar equation for Raman scattering of light by gas molecules in the atmosphere looking backwards, taking into account the finite width of the lasing line. Taking account of the finite width of the lasing line of an actual laser, and of the bands of Raman scattering of light and the hardware features of the lidar make it possible to refine the solution of such lidar equation [3], especially in the case of small concentrations of molecules being sought. The objective of this work is to estimate the measurement error by Raman lidar of the concentration on the order of units of the maximum permissible concentration of hydrofluoride molecules in the atmospheric boundary layer with altitude to 1.5 km in synchronous photon counting mode, and also to select the optimal parameters for the lidar equation of such lidar. 1 2
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