Diurnal Variation and Spatial Distribution Effects on Sulfur Speciation in Aerosol Samples as Assessed by X-Ray Absorption Near-Edge Structure (XANES).

Siwatt Pongpiachan,Phoosak Hirunyatrakul,Itthipon Kittikoon,Junji Cao,Kanjana Thumanu,Warangkana Na Pattalung,Kin Fai Ho

doi:10.1155/2012/696080

Abstract

This paper focuses on providing new results relating to the impacts of Diurnal variation, Vertical distribution, and Emission source on sulfur K-edge XANES spectrum of aerosol samples. All aerosol samples used in the diurnal variation experiment were preserved using anoxic preservation stainless cylinders (APSCs) and pressure-controlled glove boxes (PCGBs), which were specially designed to prevent oxidation of the sulfur states in PM10. Further investigation of sulfur K-edge XANES spectra revealed that PM10 samples were dominated by S(VI), even when preserved in anoxic conditions. The “Emission source effect” on the sulfur oxidation state of PM10 was examined by comparing sulfur K-edge XANES spectra collected from various emission sources in southern Thailand, while “Vertical distribution effects” on the sulfur oxidation state of PM10 were made with samples collected from three different altitudes from rooftops of the highest buildings in three major cities in Thailand. The analytical results have demonstrated that neither “Emission source” nor “Vertical distribution” appreciably contribute to the characteristic fingerprint of sulfur K-edge XANES spectrum in PM10.

Highlights

Sulfur speciation in aerosol particles plays a crucial role in both Earth’s energy balance and acid deposition [1,2,3,4,5]
There are three features which are common to each sulfur K-edge X-ray absorption near edge structures (XANES) spectrum: (a) the “pre-edge” region, which represents the energy emitted at 2450–2465 eV and points to the area of energies lower than the main absorption edge; (b) the “near-edge” region, which refers to the 5 eV wide region around the white-line, located at the “post-edge” region, which denotes the region greater than 2490 eV outside the absorption edge
Drawing from the Takahashi et al conclusion that particulate sulfur compounds are dominated by S(VI), it can be deduced that the oxidation number of elemental sulfur collected at National Institute of Development Administration (NIDA) Bangkapi campus is +6, and plausibly occupied by sulfate species

Summary

Introduction

Sulfur speciation in aerosol particles plays a crucial role in both Earth’s energy balance and acid deposition [1,2,3,4,5]. Several reference publications have indicated that the most stable oxidation state of sulfur in aerosol is +6 (S(VI)) [9,10,11,12] These findings were supported by recent experimental data suggesting that (NH4)2SO4 and CaSO4-2(H2O) are dominant sulfur species in aerosols [13]. Despite of these facts, there are several outstanding questions and information gaps which merit additional study for clarification. There are several outstanding questions and information gaps which merit additional study for clarification Such is the case for investigating the role of emission source, diurnal variation, and vertical distribution on sulfur oxidation states and on sulfur K-edge XANES spectra in PM10. Since the conversion of gaseous SO2 to particulate SO4−2 can dramatically alter the sulfur oxidation state, all ambient sulfur species are required to preserve in anoxic condition due to its relatively high oxidation rate as previously discussed in several publications [14,15,16]

Objectives

Methods

Results

Discussion

Conclusion