Panels (a) and (b) show the spectra of ¹³CO (8–7) and HCN laser emission at 891 GHz obtained in 2010 May 15. Panels (c–g) show the original 891 GHz laser spectra in the USB that were contaminated by ¹³CO (8–7) from the LSB during 2011 to 2013 (in green). The upper and lower axes indicate the frequency ranges of the blended emission in the USB and LSB, respectively. The orange curves present the fitting results for the ¹³CO contamination. Panels (h–1) show the 891 GHz laser spectra (in red) that have been removed the ¹³CO contamination.