Determination of total and non-water soluble iodine in atmospheric aerosols by thermal extraction and spectrometric detection (TESI)

Abstract

Iodine has recently been of interest in atmospheric chemistry due to its role in tropospheric ozone depletion, modification of the HO/HO(2) ratio and aerosol nucleation. Gas-phase iodine chemistry is tightly coupled to the aerosol phase through heterogeneous reactions, which are dependent on iodine concentrations and speciation in the aerosol. To date, the only method available for total iodine determination in aerosols is collection on filters by impaction and quantification by neutron activation analysis (NAA). NAA is not widely available to all working groups and is costly to commission. Here, we present a method to determine total iodine concentrations in aerosol impact filter samples by combustion of filter sub-samples (approximately 5 cm(2)) at 1,000 degrees C, trapping in deionised water and quantification by UV/Vis spectroscopy. Both quartz and cellulose filters were analysed from four separate sampling campaigns. The method proved to be sensitive (3sigma = 6 ng absolute iodine approximately 3 pmol m(-3)) precise (RSD approximately 5%) and accurate, as determined by external and standard addition calibrations. Total iodine concentrations ranged from 10 pmol m(-3) over the Southern Ocean to 100 pmol m(-3) over the tropical Atlantic, in agreement with previous estimates. The soluble iodine concentration (extracted with water and measured by ICP-MS) was then subtracted from the total iodine to yield non-water-soluble iodine (NSI). The NSI fraction ranged from 20% to 53% of total iodine, and thus can be significant in some cases.

Speciation Analysis of 129I and 127I in Aerosols Using Sequential Extraction and Mass Spectrometry Detection

“…Combustion was proposed to separate total or insoluble iodine from aerosol on quartz and cellulose filter. 19 However, our preliminary experiment shows that it is not well suited for filters of organic materials (e.g. polypropylene) because of rapid burning of organic materials at high temperature causing a low iodine recovery (< 60%).…”

“…10,19,37 However, the conventionally used tube furnace has a maximum capacity of 0.5 g PP aerosol filter that is insufficient for speciation analysis of 129 I. In addition, the rapid burning of PP filter produced gas suddenly increasing the pressure in the combustion system, causing a risk of extrusive loss of iodine during insufficient combustion, even an explosion.…”

“…Alkaline leaching using NaOH-Na 2 SO 3 , microwave-assisted acid digestion, pyrolysis and alkaline ashing have been used for extract total iodine from aerosol samples. 14,18,19,21,22 Among these methods, acid digestion with pressure or microwaveassist might cause iodine loss due to formation of volatile molecular iodine and hydrogen iodide, which are chemically active and easily react with the materials of the canister such as TEFLON. Meanwhile, the limited volume of digestion canister is incapable to treat adequate amount of filter for speciation analysis of 129 I.…”

A review on 129I analysis in air

“…For the extraction of non-water soluble iodine species, TMAH has been applied (Chen et al, 2006). Extraction of iodine species in ultrapure water using ultrasonic method and pressurized decomposition with dilute ammonia has also been reported (Gilfedder et al, 2010) to improve efficiency. Another approach to increasing the extractable yield of iodine was sulphite leaching using Na 2 SO 3 or NaHSO 3 .…”

Short-Lived Trace Gases in the Surface Ocean and the Atmosphere

“…The proportion of SOI relative to IO 3 À is quite variable, although SOI is frequently found to constitute the major fraction (Gilfedder et al 2008). There is also an appreciable insoluble fraction of aerosol iodine, which is likely to be either organic or iodine adsorbed to mineral or black carbon surfaces (Baker et al 2000;Gilfedder et al 2010;Tsukada et al 1987;Xu et al 2010 Baker 2005). The interactions of iodine and organic matter, and the degree to which aerosol iodine can be recycled to the gas phase, are the most significant unknowns in aerosol iodine chemistry at present.…”