Fig. 1. Transmittance peak types and wavelength ranges of different band-pass filters. (a) λc=458 nm, w1/2=2 nm; (b) λc=450 nm, w1/2=10 nm; (c) λc=450 nm, w1/2=40 nm

Fig. 2. Relationship between central wavelength and incident angle. (a) Transmittance spectra; (b) curve of central wavelength versus incident angle

Fig. 3. Schematic of imaging system

Fig. 4. Absorption cross section of NO2 and H2O

Fig. 5. SNRs of three filters

Fig. 6. Plume maps under different exposure time. (a) 2 s; (b) 0.5 s

Fig. 7. SNR versus exposure time and number of superimposed images

Fig. 8. Relationship between column density of NO2 and optical density. (a) λc=458 nm, w1/2=2 nm; (b) λc=450 nm, w1/2=10 nm; (c) λc=450 nm, w1/2=40 nm

Fig. 9. Detection limits of filters

Fig. 10. Master maps. (a) λc=450 nm; (b) λc=600 nm

Fig. 11. Distributions of optical density and column density of NO2. (a) Optical density of filter with central wavelength of 450 nm; (b) optical density of filter with central wavelength of 600 nm; (c) differential optical density of NO2; (d) two-dimensional column density distribution of NO2