Quantification Method for Aerosol Hygroscopicity Using a Physical Adsorption Analyzer

Atmospheric aerosol hygroscopicity, representing the capability of atmospheric aerosol to absorb water molecules, critically impacts climate. Physical adsorption analyzers are accurate techniques for measuring molecular adsorption; however, they have not been applied to atmospheric aerosol particles. In this study, we developed the application of a physical adsorption analyzer to quantitatively evaluate aerosol hygroscopicity, providing improved quantitative capability and versatility across a range of particle compositions compared with existing measurement techniques. The hygroscopic properties of five typical organic components and three common inorganic salts were systematically tested. Deliquescence relative humidity (DRH) values were obtained, demonstrating excellent agreement with existing literature. Building upon k -Köhler theory, a measurement framework was established to calibrate the particle diameter growth factor (GF) and derive the single hygroscopicity parameter ( k) from the physical adsorption data. The derived GF and k values exhibited statistically significant linear correlations with reference data, yielding coefficients of determination (R2) of 0.70 and 0.74, respectively. Except for highly hygroscopic nitrate salts, the measurement error in k was less than 0.2. Although scale corrections are necessary due to macroscopic sample morphology differences, this method offers a convenient, reliable, and complementary cross-validation approach alongside traditional techniques for characterizing atmospheric particulate matter.