Fig. 1. Simulated absorbance of different gases near 1.5 μm wavelength (T=300 K, p=9.5 kPa, L=1.6×104 m). (a) 6528.9 cm-1; (b) 6548.7 cm-1; (c) 6568.4 cm-1; (d) 6596.4 cm-1; (e) 6600.2 cm-1; (f) 6612.7 cm-1; (g) 6678.5 cm-1

Fig. 2. Simulated absorbance of different gases in range of 6520-6532 cm-1 (T=300 K, p=9.5 kPa, L=1.6×104 m)

Fig. 3. Simulated absorbance of different gases near 6521.97 cm-1 (T=300 K, p=9.5 kPa, L=1.6×104 m)

Fig. 4. Schematic of laser mode matching

Fig. 5. Transmitted cavity mode signal

Fig. 6. Schematic of CRDS experimental system

Fig. 7. Experimental gas path

Fig. 8. Acquisition and fitting of ring-down curve

Fig. 9. Absorption lines of NH3, CO2 and H2O in atmosphere in range of 6520-6530 cm-1 (T=300 K, p=9.5 kPa, L=1.6×104 m). (a) Experimental measurement data; (b) simulation results in HITRAN database

Fig. 10. Absorption coefficient of 55 sampling points obtained by measurement

Fig. 11. Absorption results of 6521.97 cm-1 NH3 and 6522.04 cm-1 H2O spectral lines after baseline deduction

Fig. 12. (a) Voigt multi-peak fitting results of NH3 and H2O absorbance; (b) fitting residual

Fig. 13. (a) NH3 concentration obtained by a continuous measurement for 400 s in outdoor environment; (b) Allan deviation