Abstract: An open multi-pass White cell system with an effective optical path of 192 m was designed in this work. By means of design simulation and optimization of Zemax, and then coupling with a mediumresolution Fourier transform infrared spectrometer, a multi-pass open optical path FTIR system was constructed. The field monitoring results showed that the detection limits of the system for CH4, NO2, O3, SO2, HCHO and NH3 gas concentration are 38.01804 nmol/mol, 23.77203 nmol/mol, 2.78154 nmol/mol, 28.08897 nmol/mol, 6.10395 nmol/mol and 1.54374 nmol/mol respectively, confirming that this design significantly improves the effective absorption optical path and reduces the detection limit of the spectrometer, and enabling online monitoring of atmospheric composition in the order of nmol/mol concentration. The establishment of the system provides a new means for environmental science research and pollution gas emission monitoring.

Key words: spectroscopy, Fourier transform infrared spectrometer, White cell, detection limit, long optical path