Do you need to measure smoke blackness at night? Why not?

Need. Because there is no definite relationship between smoke blackness and smoke content in smoke, smoke blackness needs to be measured at night, but it is not suitable for observation in rainy and snowy days, foggy days and when the wind speed is greater than 4.5 m/s, so it cannot be measured. This method can not replace the measurement of smoke content, and it is safe and reliable.