Volatile short lived Iodocarbons from biotic and
abiotic sources effecting atmospheres chemistry
U.R.Thorenz , M. Kundel, R.J. Huang, J. Petersen, N.H. Bings and T. Hoffmann
Johannes Gutenberg University, Department of Inorganic Chemistry and Analytical Chemistry, Duesbergweg 10-14, 55128 Mainz, Germany
[email protected]
Introduction:
Atmospheric Iodine radicals, formed from iodocarbons or molecular iodine, deplete
tropospheric ozone and accelerate the ozone destroying capacity of other halogen species [1].
The oxides formed during this reaction may also undergo further oxidation and form polyoxides
which then can react as cloud condensation nuclei [2]. The iodocarbons found in marine
atmosphere are mainly produced via a biotic pathway from different kinds of macro- and
microalgae. Additionally abiotic pathways of forming these reactive substances are known
[3,4]. The production of iodocarbons in atmospherical particles is discussed.
Figure1:
Iodine related
atmospheric reactions
An overview of the iodine related atmospherical reactions is given in Figure 1.
Methods:
Air samples were pre concentrated on thermal desorption tubes and measured using a self-made thermal desorption device mounted on a GC-MS. The analytes were separated
on a DB624 Durabond column. Measurement of the halocarbons was done using negative chemical ionisation mode with methane as reagent gas. Iodinated compounds (CH3I,
C2H5I, CH 2ICl, CH 2IBr, CH2I2, 1-C3H7I, 2-C3H7I, 1-nC 4H9I, 2-nC4H9I,1-iso-C4H9I) were measured using the m/z 127, whereas brominated compounds (C2H5Br, CH2BrCl, CH2Br2,
CHBrCl2, CHBr2Cl, CHBr3, 1,2-C2H4BrCl, 1,2-C2H4Br2, 1,2-C3H6Br2, 1,3-C3H6BrCl, 1,2-C3H6Br2) used m/z 79/81 in the typicall isotope ratio of 1:1.
A five point calibration was done in the range of 0.01 ng- 1.00 ng using the continuously diluted output of permeation tubes. These tubes were made by filling the pure standards
in Teflon tubes which were sealed with stainless steel balls at both ends. The method detection limit was 0,003 - 0,088 ppt. For sample measurement the calibration was done in
triplicate giving a method precision of 3-13%.
Biotic Sources :
During a measurement campaign at the Alfred Wegener Institute at Helgoland the dependency of Halocarbon and molecular iodine emission (using a TOF-AMS method, see
Poster 3095 ) on ozone mixing ratios was investigated. Different macro algae (Laminaria digitata, Laminaria saccharina, Laminaria hyperborea, Ascophyllum nodosum,
Fuccus serratus, Fuccus vesiculosus, Chondrus crispus and Delesaria sanguinea) were treated with air at different ozone concentrations to investigate weather the elevated
oxidative stress leads to higher emission. Additionally the total iodine amount of these species was measured using ICP-MS.
7
6
5
4
3
2
1
R² = 0.9043
0
0
40
80
120
160
Ozone Concentration / ppb
Figure 2:
The experiments showed an enhanced
halocarbon production of Laminaria digitata by
oxidative stress using ozonized air, Figure 2.
This was also found by Palmer et al. 2005 for
higher ozone concentrations. Other kelps
(Laminaria saccharina, Ascophyllum nodosum
Fuccus serratus and Fuccus vesicolosus)
halocarbon emissions showed no clear
relationship.
A correlation for molecular iodine and
iodocarbon emission was found. [Poster 3095]
The total iodine content and iodocarbon
emission showed a exponential trend, Figure 3.
This indicates that the emission of iodocarbons
may be limited by total iodine content.
100
10
1
R² = 0.8615
0.1
0
Figure 3:
RT: 0.00 - 35.02
95
90
85
80
Different chamber experiments were performed to investigate the abiotic pathways in
halocarbon formation. In experiment 1, Fulvic Acid and HOI were mixed and
atomized, to form particles of organic matter and oxidized iodine. These particles
passed a chamber of 70 L. In this experiment the formation of iodomethane was
observed (Figure 4). Since the Fulvic acid was already contaminated with Iodinated
compounds new experiments with other material as organic matter are planned to
verify the discussed reaction pathway via haloform reaction and to calculate constants
of formation.
1500
2000
2500
Iodocarbon emission and total Iodine
content of different algae at 50 ppb ozone
iodomethane
formed during
experiment
7.02
100
1000
Total Iodine content µg g-1
Ozone dependent emission of
diiodomethane from Laminaria digitata
Abiotic Sources :
500
75
mass trace m/z 127
Iodine in
chamber experiment
NL:
4.84E3
m/z=
126.50-127.50 F:
MS
K1_Kammerexper
imentFulvosaeure
1_06_12_2010
70
65
mass trace m/z 127
Iodine in Fulvic
acid
15.16
60
55
50
45
40
35
19.37
30
25
20
15
10
23.91
5
1.60 2.53 3.16
0
0
2
4.19
4
4.54
6
7.34 8.51
8
9.68
10
11.59 12.29
12
14.31
14
15.45
16
17.36 18.42
18
Time (min)
20.08
20
25.50
21.85 22.03
22
24
26
28.58 28.75 29.89
28
30
32.01 32.33
32
34.77
34
Time / min
Figure 4:
Formation of iodomethane in particle phase
Conclusion:
Outlook:
Oxidative stress by atmospheric relevant ozone mixing ratios enhances the
halocarbon emission
Microalgae are more abundant in the oceans and have higher impact on global
climate models, therefore also different kind of microalgae will be target of future
investigation.
The exponential trend of the iodocarbon emission and the total iodine
content indicates iodine content as imitating factor
Abiotic formation of iodocarbons by Fulvic acid and HOI as it was described
for bulk material [6] also takes place in the particle form
References:
Another abiotic model needs to be tested whereby Fulvic acid will be replaced by
benzyl alcohol to be the organic reaction partner, HOI will be replaced by I2O5.
Different factors like pH, particle diameter, temperature and educt concentration
need to be investigated.
[1] O´Dowd, C. et al. (2002) Nature, 417, 632-636 ; [2] Carpenter, L. et al. (1999). J.Geophys.Res., 104,1679–1689
[3] Mahajan, A. S. et al. (2010) J.Geophys.Res., 115,D20303; [4]Carpenter, L. et al. (2005) Environ. Sci. Technol., 39, 8812-8816
[5] Palmer, C.J. et al. (2005) Environ. Chem. 2, 282-290 ; [6] Carpenter, L et al.(2005) Environ. Sci. Technol. 39, 8812-8816