Structural characterization of fatty acid films on rain water: a scaling approach using physical attributes

A complete compositional or structural description of naturally-occurring surfactants on rain water is not currently feasible. A main limitation of previous work has been the lack of means for correlating force-area char­acteristics with the chemical makeup of the films. Instead of analyzing the chemical composition of rain water film-forming organics, it is postulated here to introduce the novel scaling procedures (2D virial equation of state and 2D polymer film scaling theory) applied to the surface pressure-area (n-A) isotherms and surface pressure- temperature (n-T) isochors and resulting from generalized physical formalisms modified to a multicomponent surfactant film. A set of the introduced structural film state parameters (n, r, Alim, Eisoth, y, R, Mw, Ps) could become sensitive indicators for surface-active source-specific organic matter pathway tracing, where the measurement of surfactant concentration and chemical analyses are avoided. The concept is quantified using the Langmuir trough film and disdrometer data on a set of rain water events observed in Gdańsk, Poland in May 2002.