相对湿度和粒子形态对海盐气溶胶粒子散射特性的影响

Effect of relative humidity and particle shape on the scattering properties of sea salt aerosols

根据海盐粒子在不同相对湿度条件下的不同形态,分别建立了低湿度(RH=0%)、中湿度(RH=50%)和高湿度(RH=95%)三种条件下海盐立方体和球形粒子模型。利用离散偶极子近似法(DDA)、Mie散射理论研究了相对湿度和粒子形态对海盐散射的特性影响,采用离散坐标法(DISORT)研究了相对湿度和粒子形态对海盐特性的影响。结果表明:相对湿度和粒子形态对海盐散射特性影响较大,不同相对湿度条件下,海盐气溶胶粒子由于相态不同,呈现出不同的特性。中湿度条件下,粒子形状因子对海盐散射辐射特性的影响更强。当光学厚度较小时,球形-立方体海盐气溶胶的双向反射分布函数(BRDF)相对差异超过15%,在研究海盐气溶胶散射辐射特性时,需同时考虑相对湿度和粒子形态的影响;当光学厚度较大时,相对差异不超过5%,一定精度范围内,可采用等效球方法进行模拟计算。研究结果对于大气气溶胶散射和辐射传输理论及应用研究具有重要的参考价值。

According to the hygroscopic characteristics and different forms of sea salt particles in different relative humidity conditions, the models of sea salt particles under three conditions were established: low humidity(RH=0%), medium humidity(RH=50%), high humidity(RH=95%). Influence of relative humidity and particle morphology on the scattering characteristic of sea salt was studied by discrete dipole approximation(DDA) method. Influence of relative humidity and particle morphology on the scattering and radiation characteristic of sea salt was studied by DDA method, Mie scattering theory and Discrete Ordinate Method Radiative Transfer(DISORT) method. The results show that relative humidity and particle morphology have great influence on the scattering characteristics of sea salt particles. Under medium relative humidity, the scattering and radiative transfer characteristics of the sea salt aerosol are more sensitive to particle shape. When the optical thickness is equal to 0.1, the relative difference of BRDF of spherical-cubic sea salt model can be more than 15%, the effect of relative humidity and particle morphology must be taken into account when studying the scattering and radiation transfer properties of sea salt aerosol. With the increase of optical thickness, the relative difference of BRDF decreases, when the optical thickness is greater than 1, the relative difference of BRDF is less than 5%, the equivalent sphere method can be used to simulate calculation within a certain precision range. These findings have important implications to the theory and application of atmospheric aerosol scattering and radiation transfer.