Biomonitoring of air quality in the Cologne conurbation using pine needles as a passive sampler—Part I: magnetic properties

Abstract

High resolution temporal and spatial control of atmospheric pollutants is of crucial importance for environmental health monitoring. Passive sampling using natural vegetation biomonitoring allows acquisition of well-defined samples at affordable costs. We here present results from a study conducted in the conurbation of Cologne, Germany, based on airborne pollutants accumulated on pine needles. This integrated study includes (i) the microscopic analysis of pine needles and analysis of their magnetic properties, (ii) PAH, and (iii) selected trace elements (Fe, Cd, Pb, Ni, Cr, Cu). A major proportion of atmospheric pollutants is bound to particles, for which in part I of the study we present data on magnetic susceptibility, remanence measurements (IRM, ARM) and total Fe content. SEM-analysis indicates that particles accumulated on needles are mostly <2.5 μm in diameter and comprise pollen or spores, mineral dust and silica-glassy or metallic spheroids. The latter were identified as magnetite with minor pyrrhotite. These particles derive from combustion of coal in power plants or fuels in vehicular engines. A close correlation of magnetic properties (susceptibility, SIRM, ARM) and Fe content shows that non-destructive, time-efficient enviromagnetics of needles serves as an excellent proxy for biomonitoring of combustion pollutants. Their spatial distribution within the conurbation of Cologne was determined for 43 locations integrated in a GIS-database. The dominant sources of fine metallic particulates (PM 2.5 ) are emissions from road traffic, including fuel combustion, corrosion and brake-wear and from railroad and tram traffic preferentially due to material wear. Parks, forests and agricultural areas show the lowest levels of pollution by magnetic particles, followed by residential areas. This implies that traffic emissions with short transportation distances (<1.0 km) are dominant in the Cologne conurbation, whereas the contribution from power plants is negligible.