根据分形理论，基于面积-周长法，通过沉降对比试验，定量表征了大气中自由沉降颗粒物的形状分形维数。通过光学显微镜获得微颗粒的几何投影图像，借助显微图像分析软件，探讨了颗粒物几何形态的分形特征，确定了颗粒物形状分形维数与沉降时间的关系，并结合大气中颗粒物的成因分析了颗粒物的特性。结果表明，大气中沉降微颗粒的形状具有分形特性，颗粒物形状的分形维数在0.869~1.048之间，随采样时间增加，颗粒物的粒度分形维数减小，分形特性不明显。同时，分析计算得知，颗粒物的分形维数值越大，颗粒物中细颗粒物越多。通过对大气中自由沉降颗粒物形状的定量描述，为描述颗粒物的变化并为颗粒物间黏附力的进一步深入研究提供了新的思路、新的途径。
Based on the Area-Perimeter Method, the fractal theory and the experiment results of free settling, the profile fractal dimensions of the free settling particles in air are calculated. Using optical microscope, the grain projection images of air particles are obtained. With an image analysis software, the grain shape of air particles and the relation between the profile fractal dimension and the settling time are obtained. An analysis is made for air particles with consideration of the special causes of their formation. It is shown that the grain shape of air particles exhibits a distinct fractal characteristic, which is getting more distinct when the grain is smaller. The profile fractal dimensions of the particle range from 0.869 to 1.048. The value of fractal dimension decreases with the increase of the sampling time, and the fractal characteristic is getting less distinct. It is found that the higher percentage of finer particles is associated with the higher profile fractal dimension value of particles. This quantitative description of the profile fractal distribution of free settling particles in air, provides a new way to predict the shape change of the grain and the adhesion force between particles.
