为研究亲水性和疏水性气溶胶的吸湿性差异引起的散射特性差异,基于热力学原理和表面吸附理论分别建立了两类气溶胶的吸湿增长模型,并利用离散偶极子近似方法计算了相对湿度为40%~90%范围内两类气溶胶的散射性质。结果表明:亲水性粒子(以4种典型的无机盐为例)达到潮解点时,粒径随相对湿度的增大呈指数增长;而疏水性粒子(以烟尘为例)的粒径随着相对湿度的增加呈现非线性缓慢增长,该结果与实验测量值基本吻合。利用上述吸湿增长模型及实测的折射率-湿度增长规律,计算分析了在粒径为0.1~1.0 μm的范围内,相对湿度与气溶胶粒子散射增长因子的关系。研究发现,潮解后亲水性粒子散射增长因子呈指数增长,相对湿度为90%时,其值增大了几十倍,且氯化钠无机盐的散射因子增长曲线与实验结果吻合较好;而疏水性粒子的散射增长因子最大增至1.07,远小于亲水性粒子的数值。上述结果为气溶胶气候效应的评估、气溶胶浓度和大气能见度的精确测量提供了一定的理论支持。

To study the differences in scattering characteristics caused by differences in aerosol hygroscopicity, hygroscopic growth models for two types of aerosol are built according to thermodynamic principles and Brunauer-Emmett-Teller theory, respectively. Based on these models, the scattering properties of aerosols at relative humidities from 40% to 90% are calculated using the discrete dipole approximation method. It is shown that when hydrophilic particles, e.g., four typical inorganic salts, reach the deliquescent relative humidity, their size increasese xponentially, whereas that of hydrophobic particles (e.g., soot) increases slowly and nonlinearly with an increase in the relative humidity. Results are consistent with experimental measurements. Using established hygroscopic growth models and the measured refractive index-humidity growth law, the relationship between relative humidity, and aerosol particle growth factor is calculated and analyzed for the particle size range of 0.1--1.0 μm. It is found that the scattering growth factors grow exponentially after deliquescence, their values increases by tens of times at 90% relative humidity, and scattering factor growth curve of sodium chloride inorganic salt agrees well with experimental results. However, the maximum scattering growth factor of hydrophobic particles is only 1.07 at the same humidity, which is much smaller than that of hydrophilic particles. These results provide theoretical support for the assessment of the climatic effects of aerosols and for accurate measurement of aerosol concentrations and atmospheric visibility.