A Detection Method for Low Concentrations of SO₂ and NO

Nitric oxide (NO) and sulfur dioxide (SO
₂
) 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 SO
₂
and NO in flue gas. In this work, an optical SO
₂
and NO measurement system was established based on differential optical absorption spectroscopy (DOAS). A cross-sensitivity band of SO
₂
and NO was selected, fast Fourier transform (FFT) was employed to decompose the differential optical density (DOD) characteristics of SO
₂
in the mixed gas, inverse FFT (IFFT) was employed to reconstruct the DOD of SO
₂
, and the interference of NO on SO
₂
was overcome. The most sensitive absorption peak but strongly interfered by SO
₂
was selected to monitor NO. A method that was employed to decompose the DOD of NO was proposed, and the interference of SO
₂
on NO was overcome. The full-scale error of system reached 0.7% for SO
₂
and NO, respectively, and the detection limit (DL) of SO
₂
and NO reached 0.36 and 0.39 ppm, respectively.