Closure Study on Measured and Modeled Optical Properties for Dry and Hydrated Laboratory Inorganic Aerosols with Mixtures of Dicarboxylic Acids
Junjun Deng, Ke Du,* , Wei Wang, , Mark J. Rood*
A laboratory-based closure study was completed to compare measured and modeled optical properties and their dependence on controlled relative humidity (RH) for inorganic salts, dicarboxylic acids, and their mixtures. The closure between measured and modeled values of the light scattering coefficients were evaluated by calculating the average relative difference (ARD) values, which revealed agreement within 8.0% for the total scattering (ssp) and 14.8% for the back scattering (sbsp) at dry RH conditions for all test aerosols. These ARD values were less than the total relative uncertainty based on the measurement and modeling approaches, indicating the achievement of closure for ssp and sbsp. Optical properties derived from ssp including: (1) the hygroscopic growth factor, fσsp, (2) the backscatter ratio, b, and (3) the Ångström exponent, å, were also compared with measured values. The ARD values between corresponding measured and modeled results for these derived optical parameters ranged from 0.1% to 30.8%. The impact of particulate organic matter (POM) on optical and hygroscopic properties of the aerosols tested here was compared to the aerosol optical and composition measurements that occurred during the New England Air Quality Study-Intercontinental Transport and Chemical Transformation field campaign. Such comparison confirmed that a larger POM mass fraction resulted in less hygroscopicity for both the ambient and the laboratory aerosols. This study evaluated closure between laboratory measurements and model calculations and validated the reliability of the model with the closure analysis. Therefore, in the future the Mie-Lorentz model can be used to calculate the optical properties and their dependence on RH for other aerosols with more confidence.
Key words：optical property, dicarboxylic acid, closure study, hygroscopic property
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Journal：Atmospheric Environment
