Evaluation and application of biomagnetic monitoring of traffic-derived particulate pollution

Inhalation of particulate pollutants below 10 mu m in size (PM(10)) is associated with adverse health effects. Here we use magnetic remanence measurements of roadside tree leaves to examine levels of vehicle-derived PM around Lancaster, UK. Leaf saturation remanence (SIRM) values exhibit strong correlation with both the SIRM and particulate mass of co-located, pumped-air samples, indicating that these leaf magnetic values are an effective proxy for ambient PM(10) concentrations. Biomagnetic monitoring using tree leaves can thus provide high spatial resolution data sets for assessment of particulate Pollution levels at pedestrian-relevant heights. Leaf SIRM values not only increase with proximity to roads with higher traffic volumes, but are also similar to 100% higher at 0.3 m than at similar to 1.5-2 m height. Magnetic and SEM data indicate that the particle populations are dominated by spherical, iron-rich particles similar to 0.1-1 mu m in diameter, with fewer larger, more angular, silica-rich particles. Comparison of the roadside leaf-calculated PM(10) concentrations with PM(10) concentrations predicted by a widely-used atmospheric dispersion model indicates some agreement between them. However, the model under-predicts PM(10) concentrations at 'urban hotspots' such as major-minor road junctions and traffic lights. Conversely, the model over-predicts PM(10) concentrations with distance from the road wherever one tree is screened by another, indicating the filtering/protective effect of roadside trees in leaf. (C) 2009 Elsevier Ltd. All rights reserved.