Fig. 1. Structure diagram of high-precision miniaturized BBCEAS system based on LED light source

Fig. 2. Diagram of influence of LED temperature drift. (a) Variation of LED light intensity with temperature; (b) variation of 460 nm light intensity with temperature and fitting diagram

Fig. 3. Control flow chart of PID adjustment algorithm based on Kalman filter

Fig. 4. Flow chart of self-tuning PID parameter program

Fig. 5. LED temperature control diagram before and after PID algorithm improvement. (a) Comparison of LED temperature control effect before and after PID improvement; (b) comparison of changes of light intensity fluctuation and temperature control adjustment accuracy after LED temperature control stabilization

Fig. 6. Mirror reflectivity calibration. (a) Mirror reflectivity calibration curve; (b) cavity loss (solid line) and effective path length (dashed line)

Fig. 7. Instrument performance evaluation comparison diagram. (a) Comparison diagram of concentration changing with time series; (b) comparison diagram of variance changing with average time; (c) comparison diagram of frequency distribution Gaussian linear fitting

Fig. 8. Accuracy evaluation. (a) Comparison of test results of different concentrations of NO₂; (b) linear relationship between preset concentration and measured concentration

Fig. 9. Real-time atmospheric measurement. (a) Comparison of real-time atmospheric measurements; (b) correlation of measurement results of BBCEAS