Ångström exponent errors prevent accurate visibilitymeasurement

Abstract. Visibility is an indicator of atmospheric transparency and is widely used in many research fields, including air pollution, climate change, ground transportation, and aviation. Although efforts have been made to improve the performance of visibility meters, a significant error exists in measured visibility data. This study conducts a well-designed simulation calibration of visibility meters, which proves that current methods of visibility measurement include a false assumption, which leads to the long-term neglect of an important source of visibility error caused by erroneous values of Angstrom exponents. This error has two characteristics. (1) Independence, in which the magnitude of the error is independent of the performance of the visibility meter. It is impossible to reduce this error by improving the performance of visibility meters. (2) Uncertainty, in which the magnitude of the error does not show a clear change pattern but can be substantially larger than the measurement error of visibility meters. It is impossible to accurately estimate the magnitude of this error nor its influence on visibility measurements. Our simulations indicate that, as errors in visibility caused by erroneous values of Angstrom exponents are inevitable using current methods of visibility measurement, reliable visibility data cannot be obtained without major adjustments to current visibility measurement methods.