A Detection Method for Low Concentrations of SO₂ and NO

Nitric oxide (NO) and sulfur dioxide (SO2) are mainly from burning fossil fuels. They are toxic gases and harmful to environment and human health. It is very important to monitor the level of SO2 and NO in flue gas. In this work, an optical SO2 and NO measurement system was established based on differential optical absorption spectroscopy (DOAS). A crass-sensitivity band of SO2 and NO was selected, fast Fourier transform (FFT) was employed to decompose the differential optical density (DOD) characteristics of SO2 in the mixed gas, inverse FFT (IFFT) was employed to reconstruct the DOD of SO2, and the interference of NO on SO2 was overcome. The most sensitive absorption peak but strongly interfered by SO2 was selected to monitor NO. A method that was employed to decompose the DOD of NO was proposed, and the interference of SO2 on NO was overcome. The full-scale error of system reached 0.7% for SO2 and NO, respectively, and the detection limit (DL) of SO2 and NO reached 036 and 0.39 ppm, respectively.