Abstract
The aim of the study was to quantify the adsorptive and thermo-elastic properties of snowmelt water surface films and their spatial-temporal evolution with snowpack structure characteristics and the entrapped surface-active organic composition. Surface pressure–area (π-A)T isotherms, surface pressure-temperature (π-T)A isochors, and stress–relaxation (π-t) measurements were performed using a Langmuir trough system on snowmelt water samples collected in a large-scale field studies performed at several industrialized and rural Tricity (Gdansk, Poland) areas at various environmental conditions and subsequent stages of the snowpack melting progress. Since the snow-melted water composition and concentrations of surface active organic matter fractions therein are largely undetermined, the force-area isotherm scaling formalisms (2D virial equation and 2D film scaling theory of polymeric films) were adapted to the complex mixture of surfactants. The surface film parameters and their spatial and temporal evolution turned out to be unequivocally related to principal signatures of the film-forming materials: surfactant concentrations (π, Alim), surface activity (Eisoth, |E|), film material solubility (R), surface material miscibility and 2D architecture complexity (y, βs), molecular thermal mobility (πk), and a timescale of the relaxation processes within the film (τi, |E|). Moreover, the parameters appeared to be correlated with snowpack structure characteristics (snow density ρ, specific snow area SSA, snow cover thickness), sample age time, and anthropogenic atmospheric contamination pressure source locations. In particular, Eisoth was found to be related to ρ and SSA, while R correlated with the solubility of film-forming organics which turned out to be long-chain fatty acids; similarly, spatial profiles of Eisoth revealed the peak values next to the areas being under a severe anthropogenic air pollution pressure. Snowmelt water films stand for a structurally heterogeneous (y > 10) interfacial system where several transition processes of differentiated time-scales (relaxation times from 7 to 63 s) took place leading to the apparent surface viscoelasticity. To sum up, the established surface rheological parameters could serve as novel indicators, based solely on physical attributes, allowing to follow the snowpack evolution, and its melting polymorphism in order to test or improve the existing snow-entrapped organics release models based on chemical analyses. The cross-correlation functional dependences of practical value remain to be established on the larger data set.
Highlights
It is concluded that snow influences the atmospheric hydrologic cycles of organic materials
It is supposed that more hydrophilic part of the organic contaminants mixture is released in an early stage of melting, the hydrophobic fraction attached to dry aerosol particles is discharged in the final melting process stages (Meyer and Wania 2008)
Since Γ = π/RT, the obtained higher surface film pressures for longer-aged snowpacks pointed to higher surface active material content while the film composition remained almost the same
Summary
It is concluded that snow influences the atmospheric hydrologic cycles of organic materials. Snow and ice melting processes affect atmospheric contamination load to marine and terrestrial systems. Snow appears to be an effective collecting and temporary storage medium of organic chemicals from the atmospheric environment. As a result of snow metamorphosis and melt processes, the contamination is concentrated in a snowpack and further snowmelt released. The problems to be addresses are as follows: what are chemical hydrophilic–lipophilic balance (HLB) of the entrapped material in the light of the snowpack morphology and to which extent the physical conditions undergoing during the melting time affect these phenomena?. It is supposed that more hydrophilic part of the organic contaminants mixture (of less surface activity) is released in an early stage of melting, the hydrophobic fraction attached to dry aerosol particles is discharged in the final melting process stages (Meyer and Wania 2008). Snowpack signatures and its evolution were topics addressed in several theoretical and experimental works
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