Fig. 1. Typical absorption spectrum of CO₂ obtained by the prototype

Fig. 2. Structure diagram (a) and schematic diagram (b) of the in-situ detection prototype based on TDLAS for dissolved CO₂ in water

Fig. 3. Linear fitting of different standard CO₂ gas concentration and absorption peak area

Fig. 4. The diagram of linear fitting (a) and relative error (b) between different standard CO₂ gas concentration and measured concentration

Fig. 5. The measured results (a) and relative frequency distribution (b) of 800×10^-6 standard CO₂ gas for 30 minutes by the prototype

Fig. 6. The time series test results of the prototype for pCO₂ in pier

Fig. 7. The testing stations information of the prototype in the east China sea

Fig. 8. The typical absorption spectrum (a) and second-harmonic (b) of CO₂ obtained by the prototype in 20 meters depth of seawater