Geochemical Markers of Stagnant Zones in an Urban Heat Island

Abstract

The paper presents data acquired by a comparative study of the vertical variability in the chemical composition and ratios of aerosol subdisperse fractions in snow layers chronologically correlated with the stratigraphically significant snowfall periods. These data highlight features of the concentrating of trace elements at reactive (geochemical) barriers in the snow profile. The ratio of three geochemically close groups of elements, such as siderophile, sulfophile, and lithophile elements, were found out to vary relatively little from one snow layer to another in the growing snow cover. Trajectory analysis of the transfer of air masses to which stratigraphically significant snowfalls were related to the observation site provides no evidence that the identified geochemical phenomenon can be explained by that the winter aerosol field that was formed above an urban area with different trajectories of air masses can be somehow inherited in the snow layers of the growing snow cover and thus affect the vertical distributions of trace elements. Evidence indicates that that the ratios of assemblages of trace elements in the discrete snow layers, which remain stable with the growth of the snow mass, can be employed as geochemical markers of stagnant zones in an urban heat island, and the method of geochemical sampling of a snow cover in its discrete layers at a rare network of urban meteorological observation sites is an efficient additional tool for studying microscale atmospheric processes and recovering information on characteristics of the transfer of pollutants in a spatially limited urban area.