A Simple Algorithm for C2H2 Real-Time Monitor in DOAS Technology

This letter proposes an algorithm for C₂H₂ continuous monitoring based on the differential optical absorption spectroscopy technique. Some factors, such as the background noise and spectrum shift, lead to significant inaccuracy in the DOAS technique. In this absorption spectroscopy frequency-domain algorithm, the gas concentration can be accurately retrieved by focusing on the gas absorption spectrum analysis from the frequency-domain perspective. Two major improvements are presented in this algorithm. First, the 1/f noise and interaction noise, which account for the background noise, can be neglected. Second, the preprocess that calibrates the absolute wavelength can be skipped without a perceptible loss of accuracy. The improved algorithm, window-absorption spectroscopy frequency-domain algorithm, has the highest accuracy with the maximum retrieve deviation as low as 10.6% in the 100-ppm sample. Owing to the exemption of preprocess, the algorithm is superior in the speed of computing and the accuracy of real-time spectrum analysis.