New correction method for the scattering coefficient measurements of a three-wavelength nephelometer

Jie Qiu,Yingli Yu,Chunsheng Zhao,Gang Zhao,Wangshu Tan

doi:10.5194/amt-14-4879-2021

Abstract

Abstract. The aerosol scattering coefficient is an essential parameter for estimating aerosol direct radiative forcing and can be measured by nephelometers. Nephelometers are problematic due to small errors of nonideal Lambetian light source and angle truncation. Hence, the observed raw scattering coefficient data need to be corrected. In this study, based on the random forest machine learning model and taking Aurora 3000 as an example, we have proposed a new method to correct the scattering coefficient measurements of a three-wavelength nephelometer under different relative humidity conditions. The result shows that the empirical corrected values match Mie-calculation values very well at all three wavelengths and under all of the measured relative humidity conditions, with more than 85 % of the corrected values having less than 2 % error. The correction method obtains a scattering coefficient with high accuracy and there is no need for additional observation data.

Highlights

Atmospheric aerosol particles directly impact the Earth’s radiative balance by scattering or absorbing solar radiation
When aerosols take up water due to hygroscopic growth with Gucheng data, this paper establishes different linear statistical relationships under different relative humidity conditions in order to estimate the correction factor (CF)
The aerosol scattering coefficient is an essential parameter for estimating aerosol direct radiative forcing, which can be measured by nephelometers

Summary

Introduction

Atmospheric aerosol particles directly impact the Earth’s radiative balance by scattering or absorbing solar radiation. Aerosol scattering and absorbing coefficients are the two most important parameters for estimating aerosol direct radiative forcing, and part of the estimation uncertainty comes from the inaccuracy in their measurements. The three-wavelength integrating nephelometer is widely employed in field measurements and laboratory studies due to its high accuracy in measuring aerosol scattering coefficients (Anderson et al, 1996). It has two primary drawbacks – namely, the angle truncation and nonideal Lambertian light source – that contribute to a certain systematic error (Bond et al 2009).

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