1. Yunseok Im and Myoseon Jang
Partitioning-Heterogeneous Reaction Consortium SOA model to Predict Aromatic SOA Formation in the Presence of NOx and SO2
Yunseok Im and Myoseon Jang
October 25, 2011
Department of Environmental Engineering Sciences, University of Florida, Gainesville, Florida.
Hello Everyone,
My name is yunseok im from university of florida.
Today, I am going to talk about the Secondary organic aerosol formation model.
And the title is the

2. Introduction Secondary Organic Aerosol (SOA)
SOA is formed by accommodation of organic compounds which are created from either atmospheric oxidation reactions associated with photochemical NOx cycles in the gas phase or particle phase heterogeneous reactions
SO2 ---> H2SO4
Heterogeneous
reactions
Preexisting
Acidic
Inorganics Kp
Secondary Organic aerosols are formed
by the oxidation of VOCs with atmospheric oxidants such as ozone and OH radicals and produce semivoltiles which can partition into the preexisting particulate matter or form new particle by nucleation.
In addition, through the heterogeneous reaction,
NH3
SOA is major component of atmospheric carbon
(20~90% of Total organic Carbon)

3. Aromatic hydrocarbons
Aromatics are major anthropogenic VOCs in urban area.
Source: Motor vehicles, Solvent use, Biomass burning
(20% of VOC emission from gasoline, Schauer et al, ES&T, 2002)
Concentration ranges of toluene in urban air : 2-39 ppb
(Finlayson-Pitts and Pitts, 2000)
Toluene
Xylene
Aromatic compounds are of great interest in the urban atmosphere
because of their abundance in motor vehicle emission and their potential for ozone formation and SOA formation

4. Motivation Effect of SO2 on SOA formation (Aromatics) (SO2 oxidation)
Current SOA models (partitioning model)
Under-predict the field observed SOA mass
There are something more than partitioning process.
Aerosol phase chemistry (Heterogeneous RXN)
Oligomerization / Acid-catalyzed-heterogeneous RXN
Currently there are some SOA formation models such as J odum’s 2 product model or Volatility basis set (VBS) model
They are basically partitioning model. And these partitioning model
Recently many studies have shown the proofs of aerosol phase chemistry and heterogeneous reaction for additional SOA formation
So, in this study,
It was tried to make a predictive SOA formation model including partitioning and heterogeneous reaction from the aromatics in the presence of SO2
Using this model, the effect of inorganic acid to the SOA formation was evaluated using Aromatic compounds and SO2.
Effect of SO2 on SOA formation
(Aromatics) (SO2 oxidation)

5. PHRCSOA model
(Partitioning-Heterogeneous Reaction Consortium SOA model)
We named the model PHRCSOA model.
Full name is partitioning-Heterogeneous reaction consortium SOA model

6. PHRCSOA Model Structure
PHRCSOA (Partitioning-Heterogeneous Reaction Consortium SOA )model
Model structure
RH + Ox  ox,1 Pox,1 + ox,2 Pox,2 + …+ ox,20 Pox,20
Gas
Gas phase reaction products
MCM
MORPHO
ij: Stoichiometric coefficient
for product groups
Aerosol
Lumping of products
OMH
Heterogeneous reaction SOA mass
OMP
Partitioning SOA mass
This is the structure of the Phrocsoa model.
The PHRCSOA model is comprised of two parts. One is gas phase kinetic model and SOA formation model .
In gas phase kinetic model,
OMAC
Acid-catalysis
OMolg
Oligomerization
OMT
Total Aerosol Mass
OMT = OMP + OMH

7. Example of Toluene oxidation of MCM
776 reactions
147 toluene oxygenated products
This is an example of toluene MCM mechanism.
In MCM,
Toluene has 776 reaction equations and the right side figure shows the first four reactions of toluene with OH radical.
As a result of simulation of total 776 reactions,
eventually, 147 oxidized products are predicted.

8. Heterogeneous Reactivity (Fast, Medium, Slow, Partitioning only)
Lumping based on vapor pressure and reactivity
i= 1 (10-6 mmHg)
i= 2 (10-5 mmHg)
i= 3 (10-4 mmHg)
i= 4 (10-3 mmHg)
i= 5 (10-2 mmHg)
Five different vapor pressure groups
Heterogeneous Reactivity (Fast, Medium, Slow, Partitioning only)
i = 1, j = H-f
i = 1, j = H-m
147 products are lumped to 20 groups based on their vapor pressure and reactivity for heterogeneous reaction.
first, for the 147 products, vapor pressured are calculated using this equation and group to the 5 groups in range of 10-2 to 10-6 mmHg.
Then each group is divided to four groups based on their heterogeneous reactiivity. Which is determined based on their molecular structures and functional groups. For example, aldehyde or multi aldehyde groups have high reactivity and alcohol or nitrate groups have low reactivity for heterogeneous reaction
i = 1, j = H-s
i = 1, j = PO
Cao and Jang, ES&T, 2009

9. Toluene + Ox  ox,1 Pox,1 + ox,2 Pox,2 + …+ ox,20 Pox,20
20 LUMPING GROUPS
147 PRODUCTS
Toluene + Ox  ox,1 Pox,1 + ox,2 Pox,2 + …+ ox,20 Pox,20
Less Volatile
Very Volatile
High Reactivity
Slow Reactivity
Vapor
Pressure 
(mmHg)
H-f
(Fast)
H-m
(Medium)
H-s
(Slow)
H-PO
(Partitioning Only)
i=1 (10-2)
α1,f
α1,m
α1,s
α1,PO
i=2 (10-3)
α2,f
α2,m
α2,s
α2,PO
i=3 (10-4)
α3,f
α3,m
α3,s
α3,PO
i=4 (10-5)
α4,f
α4,m
α4,s
α4,PO
i=5 (10-6)
α5,f
α5,m
α5,s
α5,PO
So, finally, the oxidized products are lumped to the 20 groups based on their volatility and reactivity for heterogeneous reaction and their product yield coefficient alpha values are obtained.

10. The Effect of NOx on SOA formation
NOx = 30 ppb
NOx = 150 ppb
Vapor pressure (mmHg)
Reactivity
This is the example of alpha values of toluene oxidation products at different Nox,
As shown in the figures, alpha values are different in different Nox conditions.
So, In order to account the nox effect on gas phase chemistry.

11. The Effect of NOx on SOA formation
Gas kinetic model (MCM) simulation at various NOx (10-350ppb)
Lumping
α = f (NOx) i j
i= 1
α1,F
α1,M
x x x
α1,S
α1,P
6677.8x x x
i= 2
α2,F
α2,M
α2,S
867.26x x x
α2,P
i= 3
α3,F
6319.5x x x
α3M
1105.7x x x
α3,S
x x x
α3,P
-49651x x x
α4,s
α4,M
α4,P
i= 4
α4,F
2.4111x x
α4,M
5952.6x x x
α4,S
-10021x x x
α4,P
x x
i= 5
α5,F
25062x x x
α5M
24872x x x
α5,S
20500x x x
α5,P
-14972x x x
MCM was simulated at various Nox conditions from 10 to 350 ppb,
This is the example of alpha value change based on the nox concentration for the selected lumping gouprs. Then their regression equations are calculated and applied to the following SOA model

12. PHRCSOA Model Structure
RH + Ox  ox,1 Pox,1 + ox,2 Pox,2 + …+ ox,20 Pox,20
Gas phase reaction products
ij: Stoichiometric coefficient
for product groups
Lumping of products
OMH
Heterogeneous reaction SOA mass
OMp
Partitioning SOA mass
In aerosol model, Organic aerosol formation was calculated by two process.
Partioning and heterogeneous reaction.
OMAC
Acid-catalysis
OMolg
Oligomerization
OMT
Total Aerosol Mass
OMT = OMP + OMH

13. SOA Model Concept CP Cgas Cin (OMP) OMH ORGANIC PHASE INORGANIC PHASE
GAS PHASE
SO2 oxidation H2SO4
Non
ORGANIC
PHASE
Gas kinetic model (MCM)
20 product lumping groups
INORGANIC
PHASE
Cgas CP
(OMP)
Solubility KP
Partitioning
Cin
Acid-Catalyzed
Heterogeneous
Oligomerization
OMH
Phase separation (organic vs. Inorganic)
Inorganic phase – Acid-catalyzed RXN
Organic phase – Oligomerization
(Non-volatile)

14. Model Equations Modification of the mass balance equation used in CMAQ
Schell et al., JGR, 2001
𝚫𝐎𝐌 𝑯 = 𝒊 𝒋 𝑻 𝑯,𝒐,𝒊𝒋 − 𝜷 𝟏,𝒊𝒋 𝜷 𝟐,𝒊𝒋 𝒕𝒂𝒏 𝒂𝒓𝒄𝒕𝒂𝒏 𝜷 𝟐,𝒊𝒋 𝜷 𝟏,𝒊𝒋 𝑻 𝑯,𝒐,𝒊𝒋 − 𝜷 𝟏,𝒊𝒋 𝜷 𝟐,𝒊𝒋 𝐭
Where, 𝜷 𝟏,𝒊𝒋 = 𝒌 𝑯−𝒋 𝑴 𝒊𝒏𝒈 𝟏𝟎𝟎𝟎 + 𝒌 𝒐−𝒋 𝑪 𝒊𝒏,𝒊𝒋 𝟐 𝑴 𝒊𝒏𝒈 𝑴𝑾 𝒊𝒋 𝝆 𝒊𝒏 𝟏𝟎 𝟑
𝜷 𝟐,𝒊𝒋 = 𝒌 𝒐−𝒋 𝝆 𝑶𝑴 𝟏𝟎 𝟑 𝑲 𝑷,𝒊 𝟐 𝑶 𝑴 𝑻 𝑴𝑾 𝒊𝒋 · (𝟏+ 𝑲 𝑷,𝒊 𝑶𝑴 𝑻 ) 𝟐
Acid-catalysis
Oligomerization
Excess
acidity
Inorganic
thermodynamics
Basicity of
organics
lumping parameter

15. Chamber experiments
= 104 m3
The chamber experiments have been done by University Florida atmospheric photochemical outdoor dual chamber as shown in figure. The chamber is located on the roof of the research building. So the sampling lines can directly connected to the reasearch lab just located under the chamber.
The outdoor chamber structure is dual chamber, we called east and west chamber. Each chamber is 52m3.
So, this dual structures enable us to compare two experiment in the same meteorogical conditions.
UF Atmospheric Photochemical Outdoor Reactor (UF-APHOR) dual chambers
Toluene, P-Xylene
(200ppb)
NOx
(30 ppb)
With/
without
SO2
(80 ppb)

16. Toluene Gas phase simulation vs. Exp.
Without SO2
Toluene O3
Temp: 16 – 42 oC
RH : 10 – 33 %
NOx
With SO2
Reasonably prediction
Toluene decay
O3 formation
NOx chemistry
Artificial OH radical
:2.0E+8 molecules cm-3s-1
Bloss et al : 4.0E+8
Cao et al: 4.0E+8
Toluene O3
Original MCM under-predicted the toluene decay.
Artificial OH radical is added to the mechanism.
This under-prediction of toluene decay also reported by other studies.
And they also added the artificial OH radical to the mechanism.
And the reaction rate is in similar range.
SO2
NOx

17. Toluene SOA simulation vs. Exp.
Without SO2
Exp.
OMT
Yield increase
: 20~40%
OMP
OMH
With SO2
Exp.
OMT
OMP
OMH

18. P-xylene Gas phase simulation vs. Exp.
Without SO2
P-xylene
Gas phase
simulation vs. Exp.
P-Xylene O3
Temp: 14 – 41 oC
RH : 9 – 35 %
NOx
With SO2
O3 under-prediction
Artificial OH radical
:1.7E+8 molecules cm-3s-1 O3
P-Xylene
SO2
NOx

19. P-Xylene SOA simulation vs. Exp.
Without SO2
Exp.
Yield increase
: 20~40%
OMT
OMP
OMH
With SO2
Exp.
OMT
OMP
OMH

20. Conclusion Uncertainty of Model (inorganic phase was assumed as water)
The model reasonably predicts the Experiments for Aromatics
Gas kinetics : MCM
SOA formation : PHRCSOA model.
In the presence of SO2,
30 % yield increase for SOA from Toluene and P-xylene.
Uncertainty of Model
Accuracy of gas product prediction of MCM
Solubility calculation of organic compounds on inorganic phase
(inorganic phase was assumed as water)

21. Future Work - Model evaluation for other individual SOA precursors.
and the Mixtures of VOCs.
- Application to the regional Air quality Model, CMAQ
SOA module (partitioning and Heterogeneous OM)

22. Thank you