In this paper we present a novel hypothesis for a possible formation mechanism of humic-like substances, which were shown to be ubiquitous in fine continental aerosol. It tentatively relates the formation of atmospheric humic matter to the vast pool of soil organic matter via the evaporation, condensation, and aerosol-phase polymerization of low molecular weight polar degradation products of organic debris in the soil. The theory is based on a comparative study on the chemical structure of bulk organic matter in fine aerosol and natural humic and fulvic acids and involves simplified mass flux calculations with estimated air-water equilibrium data. Although the total soil flux of all degradation products is estimated to be of the order of ng m-2s-1, which is very low and difficult to measure, it is sufficient to sustain a mass concentration comparable to that of fine organic aerosol. The results imply that the proposed formation mechanism may be a significant natural source for fine organic aerosol at continental sites. We also suppose that precursors from other anthropogenic and natural sources contribute to producing secondary humic-like polymeric matter in continental fine aerosol.