Partitioning of magnetic particles in PM10, PM2.5 and PM1 aerosols in the urban atmosphere of Barcelona (Spain).

A combined magnetic-chemical study of 15 daily, simultaneous PM10-PM2.5-PM1 urban background aerosol samples has been carried out. The magnetic properties are dominated by non-stoichiometric magnetite, with highest concentrations seen in PM10. Low temperature magnetic analyses showed that the superparamagnetic fraction is more abundant when coarse, multidomain particles are present, confirming that they may occur as an oxidized outer shell around coarser grains. A strong association of the magnetic parameters with a vehicular PM10 source has been identified. Strong correlations found with Cu and Sb suggests that this association is related to brake abrasion emissions rather than exhaust emissions. For PM1 the magnetic remanence parameters are more strongly associated with crustal sources. Two crustal sources are identified in PM1, one of which is of North African origin. The magnetic particles are related to this source and so may be used to distinguish North African dust from other sources in PM1.

The magnetic properties of particles deposited on Platanus x hispanica leaves in Madrid, Spain, and their temporal and spatial variations.

Magnetic phases are a common component of atmospheric particles and as such are being increasingly exploited in air quality studies. In this context the magnetic properties of Platanus x hispanica leaves were determined during the spring and summer months of 2001 and 2004 in Madrid, Spain. The leaves exhibited a stable magnetic signal carried by partially oxidized magnetite grains. Most or all of the material resided on the leaf surfaces as a net result of accumulation with time and removal through precipitation. Concentration and grain-size trends indicated that roads act as the source of the magnetic signal. The relationships between IRM(1T) (magnetic concentration) and the concentration of NO(x) and PM(10) showed that the magnetic signal is specific to traffic-related emissions and not to total particle mass. City-wide maps of magnetic concentration were produced which describe the medium-term net accumulation of traffic-related particles. They showed the same pattern of concentration lows and highs in both years, with lower concentrations in 2004. Consistently high values were observed in south-central Madrid, in an area of high traffic activity. The effects of precipitation make establishing quantitative relationships between magnetic concentration and air quality parameters difficult when using tree leaves as a passive sampling system. However, a qualitative relationship is maintained which permits the mapping and identification of persistent features of particle accumulation.