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.