Measurements of aerosol optical characteristics were carried out with a Photoelectric Aerosol Nephelometer (PhAN) in Beijing and at Xinglong Observatory, which is located 150 km northeast of Beijing. Aerosol size distributions were retrieved by means of the inverse problem solution. Mean volume size distributions of the fine aerosol fraction were unimodal with the maximum radius in the range 0.11–0.15 μm. Accumulation of aerosol matter in the air basin of Beijing takes place mainly due to the growth of particle size, but not their number. A simple optical method to detect aerosol nonsphericity is proposed.