IJUP08 - Universidade do Porto

Monitoring particulate matter using magnetic properties of tree
leaves in the Porto urban area and Cinfães area
H. Corrêa-Ribeiro 1
1 Department of Geology, Faculty of Sciences, University of Porto, Portugal.
Magnetic particles due to emissions by the road traffic and others human activities such as
metallurgical, cement industries, power stations burning fossil fuels and fires are the main
a cause of cardiorespiratoire diseases. The magnetic susceptibility of tree leaves has been
used as a proxy to evaluate the particulate matter quantity and the road traffic contribution.
In order to evaluate pollution levels, sampling zones were chosen in the urban area of Porto
and compared with the rural area of Cinfães. Sampling was carried out in the first week of
June, July and August 2006. Leaves from Nerium oleander, Quercus sp., Tilia sp. And
Platanus sp. were sampled on a total of 32 sites in Porto and 48 sites in Cinfães area.
Magnetic susceptibility measurements were performed using an Agico Kappabridge
(KLY-4S, Geology Department, U.P.) and the values calculated by mass. In Porto area
magnetic susceptibility mass (χ) was comprised between -4.47 and 118.22 E -9 m 3 /kg and
only one site reveals diamagnetic values. All the others present high positive susceptibility
values which indicate the presence of anthropogenic ferromagnetic particles. In Cinfães
area χ is lower and comprised between -8.13 and 13.89 E -9 m 3 /kg but the most sites
presented diamagnetic values with exception for the sites located within Cinfães village. In
August a decrease in susceptibility values was observed in Porto, probably due to the
reduction of road traffic during holidays. Quite the opposite was observed in Cinfães area,
in the same period, an increase of χ, due to the road traffic rise during holidays and also to
the fires that occurred in August. Significant positive correlation exist between χ and the
contents of Fe and Cu of leaves, showing that the magnetic properties of leaves can be
used as a preliminary index for detection of Fe and Cu pollution. These results indicate that
a magnetic survey of tree leaves, which is relatively quick and inexpensive, may be used in
addition to the municipal air quality monitoring systems to identify high-polluted areas in
urban and non-urban environments.
Keywords: environmental magnetism, magnetic susceptibility, chemical analysis.
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