Study of aluminium distribution and speciation in atmospheric particles of different diameters in Nanjing, China

Aluminium (Al) is one of the trace inorganic metals present in atmospheric particles. Al speciation study is essential to better evaluate the mobility, availability, and persistence of trace Al and Al species in the atmosphere. This paper reports Al distribution and speciation in atmospheric particles with aerodynamic diameters >10.0, 10.0–2.5 and <2.5 μm in the urban area of Nanjing, China. Urban particles were collected with a high-volume sampling system equipped with a cascade impactor, which effectively separates the particulate matter into three size ranges. Particulate Al was fractionated into five different forms (insoluble, oxide, organic, carbonate, and exchangeable species) by the modified five-step Tessierʹs sequential extraction procedure. The main points are as follows: (1) The average levels of Al in PM2.5, PM2.5–10 and PM>10 are 2.02±0.35, 3.04±0.43 and 6.32±0.76 μg m−3, respectively, with PM2.5, PM2.5–10 and PM>10 constituting respectively, 17.8±3.1%, 26.7±3.8% and 55.5±6.7% of suspended particulate matter (SPM) mass (11.38 μg m−3). (2) The vertical profile of airborne Al in the above three size fractions has been estimated. A significant increase in airborne Al concentrations was found for PM2.5, PM2.5–10 and PM>10 as the sampling height above the ground increased from 2.5 to 17.5 m; however, there was an obvious decrease in airborne Al concentrations between 17.5 and 40.0 m. The maximum mean of total Al in PM2.5, PM2.5–10 and PM>10 occurred between 12.5 and 20.0 m above the ground. (3) The distribution of Al speciation was studied. It was found that the size distribution of airborne Al species followed the order: insoluble species>oxide species>organic species>carbonate species>exchangeable species.