Confocal Microprobe Raman Imaging of Urban Tropospheric Aerosol Particles

摘要

Particulate matter with aerodynamic diameters of <1,1-2.5,and 2.5-10 mum were collected during two seasons in two urban zones situated northeast and southwest,respectively,of a lead/zinc smelter located in a former mining region of northern France.We demonstrate the effectiveness of the combined use of computer-controlled Raman mapping and multivariate curve resolution (MCR) of the Raman images to determine heterogeneous chemistry at the level of aerosol particle.The resulting molecular images of major species were found to be in accurate agreement with elemental images obtained by WDS X-ray-mapping.Environmental SEM was very useful to localize spare metal-rich particles before Raman mapping.Some spare particles containing pyromorphite (Pb_5(PO_4)_3OH) and franklinite (Zn_xFe_(3-X)O_4) mixed with mineral dust were detected at the northeast (NE) sampling site,when the wind was blowing from the west (W) sector.These particles were probably suspended in the troposphere by the action of wind or by mechanical disturbance of polluted top soils.The most abundantly encountered particles in the 10-2.5 and 2.5-1 mum fractions were found to be aggregates of NaCl,CaCO_3,CaSO_4 centre dot 2H_2O,CaMg(CO_3)_2,SiO_2,feldspar,clay minerals,alpha-Fe_2O_3,NaNO_3,and Ca(NO_3)_2 centre dot 4H_2O.Black carbon and (NH_4)_2SO_4 particles were observed predominantly in the finest fraction.It was not rare to detect Pb and Zn-rich particles in the 10-2.5 and 2.5-1 mum fractions collected at the southwest (SW) sampling site,when the wind was blowing from the NE sector.Most of these mixed particles probably result from the aggregation between PbSO_4,PbO centre dot PbSO_4,and ZnS particles emitted by the smelters and hydroscopic mineral dust during transport in the troposphere.