Iodine speciation in atmospheric aerosols in the marine boundary layer [Elektronische Ressource] / Senchao Lai

Senchao

Informations

• Publié par: johannes_gutenberg-universitat_mainz
• Publié le: 01 janvier 2008
• Nombre de lectures: 13
• Langue: English
• Poids de l'ouvrage: 5 Mo

Extrait

Iodine Speciation in Atmospheric Aerosols in
the Marine Boundary Layer







Dissertation
zur Erlangung des Grades
„Doktor der Naturwissenschaften“
im Promotionsfach Chemie

am Fachbereich Chemie, Pharmazie und Geowissenschaften
der Johannes Gutenberg-Universität Mainz




M.Sc. Senchao Lai
geb. in Chaozhou (Guangdong), V.R. China


Mainz, 2008






天行键，君子以自强不息；
地势坤，君子以厚德载物。

《易经》










As Heaven's movement is ever vigorous, so must a gentleman ceaselessly
strive along. As Earth is vast and grand, so a gentleman must embrace
everything with virtue and tolerance.

Classic of Changes


Abstract
Abstract
Iodine chemistry plays an important role in the tropospheric ozone depletion and the
new particle formation in the Marine Boundary Layer (MBL). The sources, reaction
pathways, and the sinks of iodine are investigated using lab experiments and field
observations. The aims of this work are, firstly, to develop analytical methods for
iodine measurements of marine aerosol samples especially for iodine speciation in the
soluble iodine; secondly, to apply the analytical methods in field collected aerosol
samples, and to estimate the characteristics of aerosol iodine in the MBL.
Inductively Coupled Plasma – Mass Spectrometry (ICP-MS) was the technique used
for iodine measurements. Offline methods using water extraction and
Tetra-methyl-ammonium-hydroxide (TMAH) extraction were applied to measure total
soluble iodine (TSI) and total insoluble iodine (TII) in the marine aerosol samples.
External standard calibration and isotope dilution analysis (IDA) were both conducted
-1
for iodine quantification and the limits of detection (LODs) were both 0.1 g L for
TSI and TII measurements. Online couplings of Ion Chromatography (IC)-ICP-MS and
Gel electrophoresis (GE)-ICP-MS were both developed for soluble iodine speciation.
Anion exchange columns were adopted for IC-ICP-MS systems. Iodide, iodate, and
unknown signal(s) were observed in these methods. Iodide and iodate were separated
-1
successfully and the LODs were 0.1 and 0.5 g L , respectively. Unknown signals
were soluble organic iodine species (SOI) and quantified by the calibration curve of
iodide, but not clearly identified and quantified yet. These analytical methods were all
applied to the iodine measurements of marine aerosol samples from the worldwide filed
campaigns.
-3The TSI and TII concentrations (medians) in PM were found to be 240.87 pmol m 2.5
-3 -3
and 105.37 pmol m at Mace Head, west coast of Ireland, as well as 119.10 pmol m
-3
and 97.88 pmol m in the cruise campaign over the North Atlantic Ocean, during June
– July 2006. Inorganic iodine, namely iodide and iodate, was the minor iodine fraction
in both campaigns, accounting for 7.3% (median) and 5.8% (median) in PM iodine at 2.5
Mace Head and over the North Atlantic Ocean, respectively. Iodide concentrations
were higher than iodate in most of the samples. In the contrast, more than 90% of TSI
was SOI and the SOI concentration was correlated significantly with the iodide
2concentration. The correlation coefficients (R ) were both higher than 0.5 at Mace Head
and in the first leg of the cruise. Size fractionated aerosol samples collected by 5 stage
Berner impactor cascade sampler showed similar proportions of inorganic and organic
iodine. Significant correlations were obtained in the particle size ranges of 0.25 – 0.71
m and 0.71 – 2.0 m between SOI and iodide, and better correlations were found in
sunny days. TSI and iodide existed mainly in fine particle size range (< 2.0 m) and
iodate resided in coarse range (2.0 – 10 m). Aerosol iodine was suggested to be related
to the primary iodine release in the tidal zone. Natural meteorological conditions such

I Abstract
as solar radiation, raining etc were observed to have influence on the aerosol iodine.
During the ship campaign over the North Atlantic Ocean (January – February 2007),
-3 the TSI concentrations (medians) ranged 35.14 – 60.63 pmol m among the 5 stages.
Likewise, SOI was found to be the most abundant iodine fraction in TSI with a median
of 98.6%. Significant correlation also presented between SOI and iodide in the size
range of 2.0 – 5.9 m. Higher iodate concentration was again found in the higher
particle size range, similar to that at Mace Head. Airmass transport from the biogenic
bloom region and the Antarctic ice front sector was observed to play an important role
in aerosol iodine enhancement.
The TSI concentrations observed along the 30,000 km long cruise round trip from East
Asia to Antarctica during November 2005 – March 2006 were much lower than in the
-3other campaigns, with a median of 6.51 pmol m . Approximately 70% of the TSI was
SOI on average. The abundances of inorganic iodine including iodine and iodide were
-3
less than 30% of TSI. The median value of iodide was 1.49 pmol m , which was more
-3than four fold higher than that of iodate (median, 0.28 pmol m ). Spatial variation
indicated highest aerosol iodine appearing in the tropical area. Iodine level was
-3considerably lower in coastal Antarctica with the TSI median of 3.22 pmol m .
However, airmass transport from the ice front sector was correlated with the enhance
TSI level, suggesting the unrevealed source of iodine in the polar region. In addition,
significant correlation between SOI and iodide was also shown in this campaign.
A global distribution in aerosol was shown in the field campaigns in this work. SOI was
verified globally ubiquitous due to the presence in the different sampling locations and
its high proportion in TSI in the marine aerosols. The correlations between SOI and
iodide were obtained not only in different locations but also in different seasons,
implying the possible mechanism of iodide production through SOI decomposition.
Nevertheless, future studies are needed for improving the current understanding of
iodine chemistry in the MBL (e.g. SOI identification and quantification as well as the
update modeling involving organic matters).

II Table of Contents
TABLE OF CONTENTS
ABSTRACT ............................................................................................................................................ I
1. INTRODUCTION ..............................................................................................................................1
1.1 SOURCE OF IODINE IN THE MBL......................................................................................................1
1.1.1 Volatile Organic Iodine ...........................................................................................................1
1.1.2 Elemental Iodine .....................................................................................................................2
1.2 IODINE CHEMISTRY IN THE ATMOSPHERE ........................................................................................4
1.2.1 Gaseous Processes and Tropospheric Ozone Depletion .........................................................5
1.2.2 New Particle Formation..........................................................................................................7
1.3 IODINE SINK ..................................................................................................................................10
1.3.1 Wet Deposition of Atmospheric Iodine ..................................................................................10
1.3.1 Ocean .................................................................................................................................... 11
1.3.3 Terrestrial Aqueous Environment..........................................................................................12
1.4 OBJECTIVES OF THIS WORK...........................................................................................................12
1.4.1 Method development .............................................................................................................12
1.4.2 Iodine Speciation in Marine Aerosols ...................................................................................13
2. DEVELOPMENT OF ANALYTICAL METHODS FOR IODINE SPECIATION IN MARINE AEROSOLS...........15
2.1 SAMPLING .....................................................................................................................................15
2.1.1 Sampling Objectives..............................................................................................................15
2.1.2 Sampling Techniques.............................................................................................................16
2.2 SAMPLE PRETREATMENT...............................................................................................................22
2.3 TOTAL SOLUBLE IODINE AND TOTAL INSOLUBLE IODINE MEASUREMENT IN MARINE AEROSOLS .23
2.3.1 Experimentation ....................................................................................................................25
2.3.2 Results and Discussion....................................