Abstract
The ${{\rm{NO}}_2}$-differential absorption lidar (${{\rm{NO}}_2} {\text -} {\rm{DIAL}}$) technique has been of great interest for atmospheric ${{\rm{NO}}_2}$ profiling. Comprehensive studies on measurement errors in the ${{\rm{NO}}_2} {\text -} {\rm{DIAL}}$ technique are vital for the accurate retrieval of the ${{\rm{NO}}_2}$ concentration. This work investigates the systematic errors of the recently developed continuous-wave (CW) ${{\rm{NO}}_2} {\text -} {\rm{DIAL}}$ technique based on the Scheimpflug principle and a high-power CW multimode laser diode. Systematic errors introduced by various factors, e.g., uncertainty of the ${{\rm{NO}}_2}$ differential absorption cross-section, differential absorption due to other gases, spectral drifting of the ${\lambda _{\rm{on}}}$ and ${\lambda _{\rm{off}}}$ wavelengths, wavelength-dependent extinction and backscattering effect, have been theoretically and experimentally studied for the CW-DIAL technique. By performing real-time spectral monitoring on the emission spectrum of the laser diode, the effect of spectral drifting on the ${{\rm{NO}}_2}$ differential absorption cross-section is negligible. The temperature-dependent ${{\rm{NO}}_2}$ absorption cross-section in the region of 220–294 K can be interpolated by employing a linear fitting method based on high-precision absorption spectra at 220, 240, and 294 K. The relative error for the retrieval of the ${{\rm{NO}}_2}$ concentration is estimated to be less than 0.34% when employing the interpolated spectrum. The primary interference molecule is found to be the glyoxal (CHOCHO), which should be carefully evaluated according to its relative concentration in respect to ${{\rm{NO}}_2}$. The systematic error introduced by the backscattering effect is subjected to the spatial variation of the aerosol load, while the extinction-induced systematic error is primarily determined by the difference between the aerosol extinction coefficients at ${\lambda _{\rm{on}}}$ and ${\lambda _{\rm{off}}}$ wavelengths. A case study has been carried out to demonstrate the evaluation of systematic errors for practical ${{\rm{NO}}_2}$ monitoring. The comprehensive investigation on systematic errors in this work can be of great value for future ${{\rm{NO}}_2}$ monitoring using the DIAL technique.
© 2020 Optical Society of America
Full Article | PDF ArticleMore Like This
Liang Mei, Peng Guan, and Zheng Kong
Opt. Express 25(20) A953-A962 (2017)
Jiheng Yu, Yuan Cheng, Zheng Kong, Jiaming Song, Yupeng Chang, Kun Liu, Zhenfeng Gong, and Liang Mei
Opt. Express 32(3) 3046-3061 (2024)
E. V. Browell, T. D. Wilkerson, and T. J. Mcilrath
Appl. Opt. 18(20) 3474-3483 (1979)