The scale-free network behavior of ambient volatile organic compounds.

A scale-free network model with surface and vertical field measurements was used to identify the connectivity distribution of the scale-free network behavior of ambient volatile organic compounds (VOCs). The results show that the carbon number (C(n)) with the total amount of C(n) compounds (P(C(n))) possesses an explicit relationship with the scale-free network behavior. The proportionate coefficient (α) and exponent (γ) of the scale-free network model with spatial and temporal variations are estimated and discussed. The analytical results demonstrate that although photochemical reactions cause the VOCs fraction variation, they do not alter the fraction of C(n) compounds observably. Therefore, the values of α and of γ did not vary with time, but with local regional characteristics. The results indicate that the influence of local VOCs emissions occurs at a height of 100 m, but becomes insufficient at a height of 300 m. Air mass mixing increases with greater height; thus, the influence of regional characteristics at a height of 700 m is low. Finally, a successful empirical model was established to evaluate the distribution of surface VOCs in various regions.