Influence of collection substrate and extraction method on the speciation of soluble iodine in atmospheric aerosols

Chan Yodle,Alex R Baker

doi:10.1016/j.aeaoa.2019.100009

Abstract

Abstract The extraction into aqueous solution of total soluble iodine (TSI), iodide and iodate were examined as a function of extraction times between 5 and 60 min for two different extraction methods and from two types of commonly used aerosol collection substrates. The extraction methods tested were ultrasonic agitation and mechanical shaking, while the substrates were cellulose fibre (CF) and glass fibre (GF). Tests were carried on substrates spiked with known amounts of iodide and iodate and on a pair of ambient aerosol samples collected at the University of East Anglia on both substrates over the same time period. The combination of ultrasonic agitation and CF substrates (which has been used in many published studies of aerosol iodine speciation) was shown to lead to variable recovery of iodine species and changes in speciation over extraction time. Mechanical shaking of GF substrates gave good recoveries of iodide and iodate from spiked experiments and stable speciation with time for the ambient aerosol sample. This combination is recommended for future use in the determination of aerosol iodine speciation. Mechanical shaking also appeared to be preferable to ultrasonic agitation for samples that were collected on CF substrates. The optimised conditions (mechanical shaking of GF substrates for 30 min) were applied to the analysis of samples collected during the Stratospheric ozone: Halogen Impacts in a Varying Atmosphere (SHIVA) cruise in the South China and Sulu Seas in November 2011. The results obtained showed variable proportions of iodide, iodate and soluble organic iodine species in these samples, with iodide concentrations possibly related to airmass history and background chemistry.

Highlights

The emission of volatile iodine-containing species from the sea surface is the primary route by which iodine enters the atmosphere (Saiz-Lopez et al, 2012; Carpenter et al, 2013)
The analysis of aerosol iodine speciation has been examined using two different aerosol collection substrates (CF and glass fibre (GF)) and different extraction conditions
In agreement with other studies, the combination of cellulose fibre (CF) collection substrates and ultrasonic agitation appeared to cause changes in iodine speciation and it is recommended that these conditions are avoided in future work

Summary

Introduction

The emission of volatile iodine-containing species from the sea surface is the primary route by which iodine enters the atmosphere (Saiz-Lopez et al, 2012; Carpenter et al, 2013). Iodine plays a key role in the destruction of ozone in the lower troposphere (Davis et al, 1996; Saiz-Lopez et al, 2012) and under some conditions the products of iodine – ozone interactions can lead to the formation of new atmospheric aerosol particles (O'Dowd et al, 2002; Whitehead et al, 2010). The determination of the speciation of aerosol iodine is important because it can provide information on the potential for aerosol iodine to re-enter the gas phase and contribute to further ozone destruction (Vogt et al, 1999; Pechtl et al, 2007). Knowledge of aerosol iodine speciation may offer insights into the mechanisms of iodine-containing aerosol particle formation and suggest the likely fate and availability of iodine once deposited

Methods

Results

Conclusion