[Quantitative study on errors in evaluation of trace gases by long path differential optical absorption spectroscopy].
Long path differential optical absorption spectroscopy (LP-DOAS) can be used to retrieve the concentration of trace gases based on the principle of least squares. LP-DOAS permits the sensitive measurement of concentrations of trace gases. However, the calculation of a statistically sound measurement precision still remains an unsolved problem. The absorbance of atmospheric trace gases is usually very weak, so the interference caused by the occurrence of non-reproducible spectral artifacts often determines the detection limit and the measurement precision. These spectral artifacts bias the least squares fitting result in two respects. Spectral artifacts are falsely interpreted as real absorption, and spectral artifacts add non-statistical noise to spectral residuals, resulting in a significant underestimation of the least squares fitting error. Monte Carlo method was presented to investigate the evaluation errors in DOAS spectra accurately. Residual inspection by cyclic displacement was used to estimate the effect of false interpretation of the artifact structures. The evaluation of simulated atmospheric measurement spectra shows that Monte Carlo method yields a good estimate of the spectra evaluation error. It is approximately real error, factors of errors are 1.13, but errors are ordinarily underestimated by err(LSQ), and factors of errors are 3.12.
Li
Su-Wen
SW
Key Laboratory of Environmental Optical and Technology, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China. swli@aiofm.ac.cn
Liu
Wen-Qing
WQ
Xie
Pin-Hua
PH
Zhang
Yu-Jun
YJ
Li
Ang
A
Chen
Teng-Yun
TY