Fig. 1. Schematic diagram of the SOF method

Fig. 2. Drawing (left) and photograph (right) of the tilt mirror/top mirror-PSD type solar tracker (a)^[29] and schematic diagram of the SOF system based on tilt mirror/top mirror-PSD type solar tracker (b)^[30]

Fig. 3. Schematic diagram of the SOF system (a)，external light path of the FTIR (b) and photograph (c) of the SOF system based on altitude mirror/azimuth mirror-PSD type solar tracker^[35]

Fig. 4. Schematic diagram (a)^[37], processed image of the solar disk and the aperture (blue: fitted circle) (b)^[37] and photograph of the SOF system with addition of fish-eye camera (c)^[38], based on altitude mirror/azimuth mirror-imaging feedback type solar tracker

Fig. 5. Photograph (a), optical schematic (b) and processed image of the solar disk and the aperture (green: fitted circles, red: search region for circle fitting algorithm) (c), of the altitude mirror/azimuth mirror-imaging feedback-INS type solar tracker^[42]

Fig. 6. Photograph of the SOF system based on altitude mirror/azimuth mirror-imaging feedback-INS type solar tracker developed by Zhejiang University

Fig. 7. Comparison between measurements and emission inventory values of alkanes flux for both USA^[44] and China^[54]