Application of synchrotron radiation for measurement of iron red-ox speciation in atmospherically processed aerosols

[摘要] In this study, ambient atmospheric particulate matter samples were collectedusing a size-resolved impactor sampler from three urban sites. The purposeof this study is to gain a better understanding of transformations ofaerosol-bound iron as it is processed in the atmosphere. Thus, the aerosolsamples were artificially aged to represent long-term transport (10 to 40days) or short-term transport (1 to 10 days) and were measured for iron atseveral time points. At each time point, iron was measured in each sizefraction using three different techniques; 1) inductively coupledplasma-mass spectrometry (ICPMS) for total iron, 2) x-ray absorbance nearedge structure (XANES) spectroscopy for the measurement of total Fe(II) andFe(III), and 3) a wet-chemical method to measure soluble Fe(II) and Fe(III).Prior to aging, the XANES spectroscopy results show that a majority (>60%for each size fraction) of the total iron in the PM is in the form ofFe(III). Fe(III) was shown to be a significant fraction of the soluble iron(sometimes >50%), but the relative significance of Fe(III) was foundto vary depending on the site. Overall, the total soluble iron depended onthe sampling site, but values ranged from less than 1% up to about 20%of the total iron. Over the course of the 40 day aging period, we foundmoderate changes in the relative Fe(II)/Fe(III) content. A slight increasewas noted in the coarse (>2.5 µm) fraction and a slight decrease inthe 0.25 to 0.5 µm fraction. The soluble fraction generally showed(excepting one day) a decrease of soluble Fe(II) prior to 10 days of aging,followed by a relatively constant concentration. In the short-term transportcondition, we found that the sub-micron fraction of soluble Fe(II) spikes at1 to 3 days of aging, then decreases to near the initial value at around 6to 10 days. Very little change in soluble Fe(II) was observed in thesuper-micron fraction.

[学科分类] 大气科学