various concentrations of 'sulfurous acid' and …...oxalic and „sulfurous‟ acids...
TRANSCRIPT
INVESTIGATIONS OF THE REACTIONS BETWEEN AMMONIA AND
“SULFUROUS-OXALIC ACID” AEROSOLSThomas Townsend and John R. Sodeau.
Centre for Research into Atmospheric Chemistry, Department of Chemistry,
University College Cork and Environmental Research Institute, Cork, Ireland.
Soluble trace gases such as
Ammonia, NH3, are produced from
agricultural sources and represent a
significant atmospheric pollutant in
Ireland.
„Sulfurous acid‟ aerosol exists as SO2 in three
forms. With NH3, bisulfite isomers and SO32-
were observed only at or >60% RH: indicating the
importance of H2O in the mechanism.
Oxalic and „sulfurous‟ acids together gave rise to
a variety of aerosols. Deprotonation of oxalic acid
resulted in more uptake of ammonia as opposed
to the sulfurous counterpart.
Vary the interaction times of ammonia with the
aerosols to probe mechanistic and kinetic details.
Investigate the interactions between NH3, H2SO4,
„H2SO3‟ and other organics such as malonic and
succinic acid.
Effects of particles:
Health implications when inhaled
Reduce and distort visibility
Climate change
Provide surfaces for “new” catalytic chemical reactions
Sulfurous acid (H2SO3) has never been characterised
or isolated on Earth. This is caused by the unfavourable
conditions within the atmosphere. Such conditions
(high temperature, water content and oxidation),
however, can be found on the Jupiter moons Io and
Europa. Aqueous dispersions of sulfur dioxide
(SO2.H2O) exist in the Earth‟s atmosphere.
Oxalic acid is mainly produced from biomass burning,
vehicle exhaust emissions and biogenic activity. The
aerosols formed from condensation and nucleation play
an important role in cloud and fog formation and their
radiative properties.
The main purpose of the research is to elucidate the various
mechanisms by which sulfate ions can be formed from SO2 in
aqueous aerosols relevant to the polluted atmosphere.
Hence the interaction between SO2.H2O aerosols with ammonia
over a range of concentrations and humidities was studied. Oxalic
acid was then introduced to this system at different concentrations.
S OO
Sulfur Dioxide
+ H2O
S
O
O
O
Bisulfite
H
OHSO2
S
Hydrogen Sulfonate
O
O O
H
HSO3
-O S
O
O-
NH4+
NH4+
Ammonium Sulfite
NH3
H
H
pH
2 - 7
pH
7 - 12
HO S
O
OH
Sulfurous Acid (H2SO3)
S
O-
O-
OO
Oxalic Acid
Oxalic Sulfonate?
Sulfate Ion
1%wt SO2.H2O 20%RH 0.75%wt C2H2O4 + 0.25%wt „H2SO3‟
Ammonium Oxalate spectrum
0.50%wt C2H2O4 + 0.50%wt „H2SO3‟
0.25%wt C2H2O4 + 0.75%wt „H2SO3‟
60%RH,
300ccm NH3
60%RH
1%wt SO2.H2O
+ 300ccm NH3
60%RH
Aerosol Flow
NH3/N2
Comp. Air
Unit
Humidifier
MCT
Exhaust
RH
To
FTIR
NH3
Analyser
SMPS
TSI 3081
P
Dilution Unit
Carrier Flow
Aerosol sampling NH3/NH4+ sampling
CatalyticConverter
Denuder
Aerosol
Generator
Aerosol Flow
NH3/N2
Comp. Air
Unit
Comp. Air
Unit
Humidifier
MCT
Exhaust
RH
To
FTIRFTIR
NH3
Analyser
SMPS
TSI 3081
SMPS
TSI 3081
P
Dilution UnitDilution Unit
Carrier Flow
Aerosol sampling NH3/NH4+ sampling
CatalyticConverter
DENUDER Coated with
oxalic acid, removes NH3(g)
Aerosol GeneratorRELATIVE HUMIDITY
(RH) tuned between 1% and 70%.
PARTICLE SIZER (SMPS)
Monitors aerosol fraction,
particle size, mass, surface
area, volume.
INTRODUCTION
RESULTS: „H2SO3‟ RESULTS: „H2SO3‟/C2H2O4
INSTRUMENTATION
CONCLUSIONFUTURE OUTLOOK
FTIR: SO2 is produced from “sulfurous acid”. in three
different forms, aqueous, liquid and gas (1347,1356,1373 cm-1)
Bisulfite isomers (1200 and 1030cm-1) and sulfite (950cm-1) are observed on the introduction of NH3 at high humidities.
Aqueous „Sulfurous‟ and oxalic acids with ammonia gave complex IR spectra suggesting the formation of reactive metastable intermediates possibly including “oxalic sulfonate”.
NOx Monitor: An increase of 0.1ppm [NH4]+ occurs to
SO2.H2O, due to the formation of ammonium sulfite which favours alkaline conditions as opposed to the HSO3
-/OHSO2-
isomers (bisulfite and hydrogen sulfonate).
The organic component (C2O42-) leads to more [NH4]
+
formation, especially at high humidities possibly due to H+
production from deprotonation.
There is less uptake of NH3 by sulfurous-dominating solutions at higher humidities.
SMPS: Humidity appears to increase the amount and size of particles for „H2SO3‟. Increased [NH3] results in smaller particle numbers with larger diameters suggesting more extensive incorporation of ammonia.
Oxalic-dominant solutions appear to produce larger sized but smaller amounts of particles when humidity was raised implying H2O uptake.
Bimodal distributions were evident at equal concentrations suggesting production of aerosols with different components.
DISCUSSION
ACKNOWLEDGEMENTS!: I would like to thank the following funding
institutions for supporting this research, as well as the CRAC lab crew!
Various concentrations of 'Sulfurous acid' and
Oxalic acid with Ammonia at high humidities
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0 50 100 150 200 250 300 350Ammonia ccm
[NH
4]+
pp
m
0.75%wt sa and 0.25%wt oa 0.5%wt sa and 0.%%wt oa0.75%wt oa and 0.255wt sa
Effect of humidity on [NH4+] for 0.75%wt oxalic
and 0.25%wt'sulfurous'
0
0.05
0.1
0.15
0.2
0 10 20 30 40 50 60 70% Humidity
[N
H4]+
0.25%wt 'sulfurous acid' and 0.75%wt oxalic acid
0.00E+00
5.00E+05
1.00E+06
1.50E+06
2.00E+06
2.50E+06
3.00E+06
3.50E+06
1 10 100 1000particle diameter (nm)
co
nc
. (d
N#
cm
3)
at dry conditions 55%RH and with 300ccm ammonia left longer
'Sulfurous acid' SO2.H2O at various conditions
0.00E+00
2.00E+05
4.00E+05
6.00E+05
8.00E+05
1.00E+06
1.20E+06
1.40E+06
1 10 100 1000Particle Diameter (nm)
co
nc
. (d
N #
cm
3)
Dry sulfurous acid Wet sulfurous acid Wet sulfurous acid and ammonia
AEROSOL FLOW-REACTOR
Made of glass, ID: 10cm, maximal
reactive length Z: 80cm.
Operated at room temperature and
atmospheric pressure.
FTIR Digilab FTS 3000
using an MCT detector
and BaF2 windows:
monitors both gas and
aerosol condensed phase.
0.75%wt SO2.H2O and 0.25%wt C2H2O4
0.00E+00
5.00E+05
1.00E+06
1.50E+06
2.00E+06
2.50E+06
3.00E+06
3.50E+06
1 10 100 1000particle diameter nm
co
nc. (d
N #
cm
3)
Solution on 100ccm ammonia 200ccm ammonia 300ccm ammonia
20%RH
0.5%wt oxalic and 'sulfurous' acid
0.00E+00
5.00E+05
1.00E+06
1.50E+06
2.00E+06
2.50E+06
3.00E+06
3.50E+06
4.00E+06
4.50E+06
1 10 100 1000particle diameter nm
co
nc. (d
N #
cm
3)
solution on 100ccm ammonia 200ccm ammonia 300ccm ammonia
20%RH
Aerosols are tiny particles suspended in the air. Those larger
than about 1μm in size are mainly produced by windblown
dust and sea-spray. Aerosols smaller than 1μm are mostly
formed by condensation processes e.g. conversion of SO2 gas
released from volcanic eruptions to sulfate-type particles.
OO-
O-O
CC
Ammonium Oxalate
NH4+
NH4+
H3O+
H3O+
→NH3 ,H2O
H3O+
H2O
O
O
CC
OH
OH
O
O
C
OH
C S
O
O
O-
AIM OF THIS WORK
H3O+
CHEMILUMINESCENCE
NOx Monitor. Catalytic
oxidation of NH3/NH4+ to NO.
AMMONIA
(100ppm standard,
NH3/N2) diluted to ppb
range. Admitted to flow
tube via a 6mm diameter
movable, glass injector.
AEROSOL GENERATION
„H2SO3‟/C2H2O4 aerosol
generated by passing a flow
(200-500 ccm) of air over a
heated solution or via a
nebuliser.