Particle pollution e An environmental magnetism study using biocollectors located in northern Portugal Helena Sant’Ovaia a, * , Maria João Lacerda a , Celeste Gomes b a Department of Geosciences, Environment and Spatial Planning, Geology Centre from Porto University, Faculty of Sciences, Rua do Campo Alegre, 4169-007 Porto, Portugal b CGUC, Department of Earth Sciences, Faculty of Sciences and Technology, University of Coimbra, Largo Marquês de Pombal, 3000-272 Coimbra, Portugal highlights < Magnetic properties were compared in leaves collected in rural and urban areas. < In urban areas magnetite-like particles dimensions range between 1 and 9 mm. < The magnetic particles are adsorbed by the leaf and deposited on its surface. < Magnetic particles are due to heavy traffic. < Leaves magnetic properties provide a tool to determine particle pollution. article info Article history: Received 25 July 2011 Received in revised form 25 July 2012 Accepted 28 July 2012 Keywords: Environmental magnetism Leaves Magnetic parameters Particulate matter abstract In this study the magnetic properties of tree leaves were measured in order to compare their capability to accumulate particles, to establish the relationship between magnetic properties and chemical data and to assess the particle pollution in selected locations in the cities of Braga, Porto, Valongo and Trancoso- Reboleiro, northern Portugal. In Porto, Braga and Valongo, leaves from the evergreen Nerium oleander were sampled each month during a year. N. oleander and deciduous Quercus spp. and Platanus spp. samples were collected in the same site in Porto, in order to determine the ability of these different leaves to accumulate particles. The leaves of deciduous Tilia spp. were collected in Porto and in a rural area (Trancoso-Reboleiro) so that a comparison could be established between them. The results indicated a contrast between the urban and the rural areas. The highest concentration of magnetic particles was found in the sampling site of Valongo and the lowest concentration in the sampling site of Trancoso- Reboleiro. In Porto, the results have shown that the Quercus leaves possessed the highest capability to accumulate particles even though it is a deciduous species. The IRM acquisition curves and the S-300 ratios found in the samples of the urban areas indicated the presence of magnetite-like structures. SIRM/ c ratio revealed particles whose dimensions ranged between 5 mm and 8 mm in urban areas. The chemical elements copper and iron have a significant positive correlation with c and SIRM, which highlights the use of magnetic properties as a proxy for the concentration of these metals in atmospheric dust. The magnetic properties were interpreted taking into consideration the rainfall peaks and then compared with the PM10 concentration levels monitored in an air quality station in Porto. Our data corroborated that magnetic properties provide a fast and inexpensive tool to evaluate long-term urban pollution from anthropogenic origin, especially heavy traffic. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction In recent decades, a great deal of importance has been given to the use of magnetic parameters in environmental air pollution studies (e.g., Verosub and Roberts, 1995; Dekkers, 1997; Matzka and Maher, 1999; Maher and Thompson, 1999; Evans and Heller, 2003). Generally, air quality is measured by specialized monitoring stations for different gases and suspended particles, especially PM10 or particulate matter of less than 10 mm. Nevertheless, the existence of a limited number of these stations in the cities neither allows the production of high-resolution spatial distribution maps of air pollution in the urban areas, nor the comparison between * Corresponding author. Tel.: þ351 22 0402489. E-mail address: hsantov@fc.up.pt (H. Sant’Ovaia). Contents lists available at SciVerse ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.atmosenv.2012.07.059 Atmospheric Environment 61 (2012) 340e349