new pathways of the reaction of oh radicals with dimethyl ...ch 3sch 2oo isomerization products (oh...
TRANSCRIPT
Vienna, 6.05.2020
New pathways of the reaction of OH radicals with dimethyl sulfide
based on CH3SCH2OO isomerization
HOOCH2SCHO + OHSO2,etc.
95%
OH
65%HO2
NO/RO2CH3SCH2O
CH3SCH2OOH
- HCHOCH3S
OH OH
OH + S
•O2CH2SCH2OOH
MSA,SO2,etc.OH
S OO
isomeriizzaat
ionpaathway
T. Berndt,1 W. Scholz,2 B. Mentler,2 L. Fischer,2 E. H. Hoffmann,1 A. Tilgner,1
N. Hyttinen,3 N. L. Prisle,3 A. Hansel,2 H. Herrmann1
1 Leibniz Institute for Tropospheric Research (TROPOS), 04318 Leipzig, Germany.2 University of Innsbruck, 6020 Innsbruck, Austria.3 University of Oulu, 90014 Oulu, Finland.
Motivation
DMS- Largest natural sulfur source to the Earth´s atmosphere- Estimated emission rate: (10 - 35) ´ 106 metric tons of sulfur per year over the oceans
Lana et al., Global Biochem. Cy.(2011)- Gas-phase oxidation mainly initiated by the reaction with OH radicals
-> formation of sulfuric acid (H2SO4) and methane sulfonic acid (MSA)- Concentration over the oceans: a few 109 molecules cm-3
- Also emission from soil/vegetation over the continents- Biomass burning in Australia: DMS: 9 x 1011 molecules cm-3 (max.)
DMDS: 3 x 1012 molecules cm-3 (max.)Meinardi et al., GRL(2003)
Reduced sulfur compounds- H2S, OCS, CS2, CH3SH, CH3SCH3, CH3SSCH3
DMS degradation - knowledge in literature (beginning of 2019)
Barnes et al.,Chem. Rev.(2006)
But: results from QC calculations point to rapid CH3SCH2OO isomerization
CH3SCH2O2 (+ O2) ® O2CH2SCH2OOH (1)
O2CH2SCH2OOH ® {HOOCH2SCHOOH} ® HOOCH2SCHO + OH (2)
k1(293 K) = 2.1 s-1; k2(293 K) = 73 s-1
Wu et al.,JPC A(2015)
Experiment
Free jet flow system- 1 bar purified air- Residence time: 3.0 - 7.9 s- “early stage” of a reaction- RO2 radical formation/isomerization- Controlled bimolecular RO2 steps- benefit: „wall-free“ conditions
CI-APi-TOF mass spectrometry- Boulder-Typ inlet system- Detection limit: 103 - 104 molecules cm-3
- Different ionisation schemes:Iodide (I-) / CH3COO- -> clustering with S-speciesRNH3
+ -> clustering with SO3 (indirect OH)(CH3C(O)CH3)H+ -> proton transfer reaction
NH4+-CI3-TOF (Innsbruck)
Observed products from CH3SCH2OO isomerization
OH via O3 + TME OH via i-C3H7ONO photolysis
- I--CI-APi-TOF analysis - reacted DMS: 4.5´107 molecules cm-3 and
reacted DMS-d6: about 2.8´107 molecules cm-3
-> k(H-shift) / k(D-shift) about 15
- I--CI-APi-TOF analysis - reacted DMS: 2.5´108 molecules cm-3
- C2H6O4S: HOOCH2SCH2OOH formedvia HO2 + O2CH2SCH2OOH ?
CH3SCH2O2 (+ O2) ® O2CH2SCH2OOH (1)
O2CH2SCH2OOH ® {HOOCH2SCHOOH} ® HOOCH2SCHO + OH (2)Wu et al.,JPC A(2015)
230 240 250 260
0.0
0.5
1.0
DMS-d6
DMS
(O2CH
2SCH 2OO
H)I-
(HOO
CH2SC
HO)I-
signa
l (cp
s)
mass / charge (Th)220 230 240 250
0
2
4
6
(C2H 6O 4S)
I-
(O2CH
2SCH 2OO
H)I-
(HOO
CH2SC
HO)I-
signa
l (cp
s)mass / charge (Th)
CH3SCH2OO isomerization products (OH via O3 + TME)
0 2x107 4x107 6x1070.0
0.0005
0.0010
HOOCH2SCHO
O2CH2SCH2OOH
reacted DMS (molecules cm-3)
norm
alize
d sig
nal
0.0 5.0x108 1.0x109 1.5x1090
5x10-5
1x10-4
C2H6O4SO2CH2SCH2OOH
HOOCH2SCHO
norm
alize
d sig
nal
reacted DMS (molecules cm-3)
NH4+-CI3-TOF (Innsbruck) (CH3C(O)CH3)H+-CI-APi-TOF
0.0 5.0x108 1.0x109 1.5x1090.0
0.004
0.008HOOCH2SCHO
reacted DMS (molecules cm-3)
norm
alize
d sig
nal
0 50 100 150
0.0
0.0005
0.0010
(O2CH2SCH2OOH)I -
(HOOCH2SCHO)I -
TME
and
DMS
off
C 3H 8 off
C 3H 8 on
DMS
onTM
E on
O3 on
norm
alize
d sig
nal
measurement cycle
I--CI-APi-TOF
→reacted DMS: 4.5´107 molecules cm-3
CH3SCH2OO isomerization rate
Competition kinetics:- Signals of O2CH2SCH2OOH and HOOCH2SCHO = f(NO) -> k1 / k3 if k2 >(or better: >>) k1
But: NO addition changes HOx system-> NO + HO2 -> OH + NO2
-> measurement of the integral OH conc. via SO3 formation from OH + SO2- low SO2 addition: r(OH+SO2) / r(OH+DMS) = 0.05- SO3 formation allows to account for rising OH conc.
-> k1 / k3 = (2.1 ± 0.4)´1010 molecule cm-3 (HOOCH2SCHO)(1.5 ± 0.3)´1010 molecule cm-3 (O2CH2SCH2OOH)
-> k1 = 0.23 ± 0.12 s-1 at 295 ± 2 K (k3 from literature)
0 1x1010 2x1010 3x1010 4x1010 5x10100
1
2
3
4
HOOCH 2SCHO
O2CH2SCH2OOH
[NO] (molecules cm-3)
prod
uct /
reac
ted
DMS
(arb
itrar
y)
A)
B)0.0001
0.001
0.01HO2
SO3
HOOCH2SCHO
O2CH2SCH 2OOH
norm
alize
d sig
nal
CH3SCH2O2 (+ O2) ® O2CH2SCH2OOH (1)O2CH2SCH2OOH ® {HOOCH2SCHOOH} ® HOOCH2SCHO + OH (2)CH3SCH2O2 + NO ® products (3)
Experiment- OH via i-C3H7ONO photolysis
OH radical recycling
-> constant OH formation rate via i-C3H7ONO photolysis-> constant OH consumption rate via OH + DMS/organic
-> measurement of the integral OH conc. via SO3 formation from OH + SO2
-> enhanced integral OH signal for OH + DMS-> OH recycling
CH3SCH2O2 (+ O2) ® O2CH2SCH2OOH (1)O2CH2SCH2OOH ® {HOOCH2SCHOOH} ® HOOCH2SCHO + OH (2)
0 50 100 150 200 2500.0
0.002
0.004
0.006
0.008no hydrocarbon
OH + DMS
OH +
α-p
inene
OH +
dec
alin
OH +
TM
E OH + DMS
photolytic OH formation and SO2 on
norm
alize
d SO
3 sign
al(in
tegr
al OH
sign
al)
measurement cycle
no DMS
Updated scheme
Berndt et al., JPC Lett.(2019)
DMSOH +
CH3SCH2O2CH3S(OH)CH3O2
X-XO
HO2 -O2
CH3SCH2OOH
CH3SCH2O
CH3S
-HCHO
O2,O3
products(MSA, SO2, etc.)
O2
products
isomerizationO2
O2CH2SCH2OOHisomerization
HOOCH2SCHO
-H2O
-HO2
CH3S(O)CH3
O2
CH3S(OH)CH3
DMSO
-O2
O2
addition channel 35%
abstraction channel 65%
-OH
products(SO2, etc.)
OH
-> Supported by measurements from field campaigns of U.S. and U.K. groupssee: Veres et al.,
P.N.A.S.(2020)
Summary
• Rapid two-step CH3SCH2OO isomerization process forming finallyHOOCH2SCHO
• Isomerization rate outruns “traditional” bimolecular CH3SCH2OO reactions with HO2, NO, RO2
• Still open question: Formation of SO2 and MSA• A next example for a rapid unimolecular RO2 pathway
important for atmospheric conditions
-> Improved techniques allow a more direct insight into a reaction!
Thanks!
K. Pielok
A. Rohmer
Thank you for your attention!
N. Hyttinen
W. ScholzB. MentlerL. Fischer
ACD modeling group (TROPOS)