INVESTIGATION OF THE
HETEROGENEOUS REACTION BETWEEN
AMMONIA, SULFATE/BISULFATE AND
SULFURIC ACID AEROSOLS
Colette Noonan
Dr Arnaud Allanic and Prof John R. Sodeau
Centre for Research into Atmospheric Chemistry
CRAC, University College Cork
Environmental Research Institute, Cork
AEROSOLS
Typical
aerosols
Visibility
reduction
dueortosolid
light
reduction
• Suspensions
ofatmospheric
liquid
particles in gas
1979
• Man-made or natural
• Why study particles?
g/m3
Particulate
Conc.
7
Forest
fires
10 μm < Ø
2003
3 μm < Ø < 10 μm
Particulate
Conc. 12 g/m3
Soil erosion
1. Health effects
0.03 μm < Ø < 3
μm
2. Visibility
Most of the aerosol mass is deposited in the upper
Particulate while
Conc.
21 highest
g/m3 effects
Particulate
Conc. 65
g/m3
airways,
the
numbers
deposit
in
alveoli
3.
Climate
Volcano eruptions
Industrial activities
SULFATE PRODUCTION IN
THE TROPOSPHERE
O2
HOSO2
H2 O
SO3
H2 SO4 (g)
GAS
OH
SO2
H2O2, O3, O2, OH, NO2
Condensation
Nucleation
SO42-
AQUEOUS
AEROSOL
????????
Roughly 4% of the S
emitted by combustion
sources is sulfate.
AMMONIA IN THE TROPOSPHERE
5 x 1010 kg per year emitted
to
atmosphere
S
E
C
REDU ENTAL
RONM TION
I
V
N
E
IFIC A
ACID
ONIA
M
M
A
NCE S
A
H
N
E
IC LE
PART ION
AT
FORM
LE I N E
O
R
Y
KE
LFAT
U
S
/
E
AT
NITR I TIONIN G
PART
SULFATE AND AMMONIA
INTERACTION IN THE TROPOSPHERE
Ammonia
OBJECTIVES OF THIS WORK
Using NH3(g) as a trace gas we are looking at:
Interaction with sulfuric acid aerosol
Determinin
g uptake
coefficient
Determining
effect of
humidity on
reaction
Using FTIR to help follow the
mechanism of reaction
Experimental Setup
Dilution Unit
P
Aerosol
Generator
Humidifier
Aerosol Flow
Carrier Flow
Z0
Comp. Air
Unit
Z1
SMPS
TSI 3081
NH3
Analyser
Z2 NH3/N2
Z3
FTIR
MCT
Catalytic
Converter
Aerosol sampling
NH3/NH4+ sampling
Exhaust
Denuder
RH
To
DETECTION 1: NOx BOX
NH3 on
Diffusion separator
NH3
NH3 off
Chemiluminescence
Cell (NOx Box)
Flowtube
Denuder coated
with Oxalic acid
NH4+
750oC
Z0
4NH3 5O2
Z1
Z2
Yb/P r/Cuoxides,750o C
NO O3
*
2
NO
*
2
NO
NO2 h
Lanthanide oxides
doped with copper
Z3 oxides
4NO 6H2O
O2
f
Determination of uptake (γ)
Surface area
of particle
d NH4
dt
kr NH4
Mean molecular
speed of
ammonia
" Wall losses"
Ln([NH4]/[NH4]o)
γ
4k r
A c
1st order rate coefficient
First- order rate
coefficient, kr:
kr
Aerosol on
0
0/zo
Time (s) / injector
position
values at
25% RH (Relative Humidity)
Aerosol
0.1% w NaHSO4
1.1*10-5
0.1% w Na2SO4
No uptake
0.1% w NaHSO4 +
0.2% w H2SO4
H2SO4
9*10-5
4*10-3
DETECTION 2: SMPS
Scanning Mobility Particle Sizer
H2SO4 / H2O aerosol sizing
9.00E+05
8.00E+05
7.00E+05
6.00E+05
5.00E+05
4.00E+05
3.00E+05
2.00E+05
1.00E+05
0.00E+00
1%
Relative
Humidity
Number NH3 off
10
100
Mean size
Number- coarse mode
306 nm
1000
Diameter (nm)
8.0E+03
Mean size
27nm
50%
Relative
Humidity
Number (/cm3)
Number (/cm3)
Number transition 02 Sept 03 (c)
6.0E+03
Number- coarse
mode
4.0E+03
2.0E+03
0.0E+00
10
100
Diameter (nm)
1000
H2SO4 /H2O / NH3 aerosol sizing
Mean size
33 nm
Number transition
2.0E+06
1.5E+06
Number pre
1.0E+06
Number post
1% Relative
Humidity
5.0E+05
0.0E+00
100
Number Transition
1000
Diameter (nm)
2.0E+05
Mean size
38 nm
50%
Relative
Humidity
7.0E+03
6.0E+03
5.0E+03
4.0E+03
3.0E+03
2.0E+03
1.0E+03
0.0E+00
1000
1.5E+05
1.0E+05
5.0E+04
0.0E+00
10
100
Diameter (nm)
Number post
Number pre
Number pre
(/cm3)
10
Number post
(/cm3)
Number (/cm3)
2.5E+06
DETECTION 3: FTIR
Sulfuric Acid Aerosol
1.6% water
H2O
36% water
H3O+
HSO4-
Gaseous ammonia with water
1.5% water
4
2
No “condensation nuclei” available to form aerosol
Ammonium sulfate and bisulfate
aerosol
SO42-
Sulfate
NH4+
Bisulfate
HSO4-
H2SO4 /H2O / NH3 aerosol IR (1)
NH4+
36% water
SO42-
H2SO4 /H2O / NH3 aerosol IR (2)
NH4
SO42-
+
HSO4-
29% water
NH3…H2O
H2SO4 /H2O / NH3 aerosol IR (3)
1.6% water
NH4+
HSO4SO3?
SO42-
NH3…H2O
CONCLUSIONS: UPTAKE
No sulfate uptake but bisulfate system is reactive
IR data indicate that uptake proceeds via an NH4+
forming reaction. Likely mechanism:
NH3(g) + H2SO4(s)  (NH4)HSO4(s) (1)
(NH4)HSO4(s) + NH3(g)
 (NH4)2SO4(s)
(2)
Based on the γ measured for NaHSO4, step (2)
is slow and therefore rate controlling
CONCLUSIONS: MECHANISM
At high %RH (>35%): reaction “complete” and
only production of [NH4]2SO4 is observed by
FTIR
At lower %RH (< 30%): the bisulfate intermediate
is observable as well as interfacial, NH3…H2O.
At very low %RH (<2%) the possible release of SO3
is observable.
This is the first experiment to follow the full details
of this “simple” chemistry on an aerosol
ACKNOWLEDGEMENTS!
Prof John Sodeau
Dr Arnaud Allanic
All the crew in the CRAC lab
Enterprise Ireland
56th Irish Universities
Chemistry Research Colloquium
University of Limerick
23rd-25th June 2004
Uptake, Accommodation and
Reaction
NH3
H2SO4
36-50%
1-2%
water
water
NH3…H2O
SO3 ?
HSO4-
NH4+
SO42-
Mean
Meansize
size =38nm
=33nm
NaHSO4 /H2O / NH3 aerosol IR
+
NHHSO
4
4
1.6% water
NH4+
SO3?
HSO4SO42SO42-
NH3…H2O
Aerosol
Flow
Carrier
Flow
Entrance region
Turbulent mixing
Movable
Injector
Laminar flow
conditions
NH3/N2
z
Reaction
region
Sampling
line