The SO₂ and NO_x emitted from boilers significantly impact air quality, and the accurate detection of their emission concentrations is crucial for environmental protection. Ultraviolet differential optical absorption spectroscopy (UV-DOAS) has become an important technique for detecting SO₂ and NO_x emissions due to its advantages, such as high sensitivity and strong anti-interference capability. Normally, portable detection devices of SO₂ and NO_x emissions use deuterium lamps as light sources. However, the mutual interference between NO and NO₂ is unavoidable within the spectral range (180~400 nm), and the detection accuracy is reduced. This paper proposes a dual-light source detection method based on differential absorption spectroscopy of SO₂, NO, and NO₂ concentrations. The high-pressure deuterium lamp and LED are combined to extend the spectral range, and polynomial fitting, wavelet filtering, and least squares method are used to retrieve concentrations from spectral data in the ranges of 295~305 nm (SO₂), 220~230 nm (NO), and 425~450 nm (NO₂). Linear corrections are implemented for high-concentration deviations of SO₂ and NO and low-concentration NO₂ to achieve high-precision quantitative analysis of single-component gases across a wide concentration range. Finally, a mixed gas spectral resolution model was established to address the spectral overlap between SO₂ and NO in the 220~230 nm range, then enables simultaneous concentration detection of mixed gases within ranges of 0～1 000 ppm (SO₂), 0～500 ppm (NO), and 0～500 ppm (NO₂). The lowest detection limits of these three gases were 0.394, 0.30, and 0.78 ppm respectively, with a relative uncertainty of 1.00%.