Check and calibration of three-wavelength integration nephelometer

Based on long-term observations at the Semi-Arid Climate Observatory and Laboratory (SACOL), check and calibration of three-wavelength integration nephelometer that measured the scattering characteristics of aerosol were discussed. The selection of checking and calibration gases was discussed, and zero gas was clean air that filtrated by high-efficiency particulate air (HEPA) filter, and calibration gas was CO2. The theory of zero and span checking was summarized, and Zero checking was done every day, and zero set was done if ranges of scattering coefficient and average values were out of ±3 Mm-1 and ± 1.5 Mm-1, respectively. Span check was done every 3~5days, and span calibration was done if the scattering coefficient error between average and theoretical calculation was greater than ± 5%. Lastly, the method for zero and span calibration was described.