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

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)

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

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)

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

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

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. http://mcm.leeds.ac.uk/MCM/browse.htt?species=TOLUENE

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

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.

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.

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 -784.41x3 + 56.704x2 - 1.3875x + 0.0172 α1,S α1,P 6677.8x3 - 451.6x2 + 8.0669x + 0.0162 i= 2 α2,F α2,M α2,S 867.26x3 - 46.81x2 + 0.3279x + 0.0099 α2,P i= 3 α3,F 6319.5x3 - 424.58x2 + 7.563x - 0.0003 α3M 1105.7x3 - 68.122x2 + 0.7903x + 0.0177 α3,S -401.87x3 + 43.206x2 - 1.5424x + 0.0197 α3,P -49651x3 + 3283.3x2 - 65.29x + 0.4762 α4,s α4,M α4,P i= 4 α4,F 2.4111x2 - 0.1293x + 0.0019 α4,M 5952.6x3 - 387.47x2 + 6.3498x + 0.0289 α4,S -10021x3 + 663.49x2 - 15.313x + 0.2143 α4,P -20.733x2 + 0.7243x + 0.026 i= 5 α5,F 25062x3 - 1682.7x2 + 34.584x + 0.1777 α5M 24872x3 - 1648.6x2 + 32.532x + 0.2432 α5,S 20500x3 - 1337.1x2 + 26.141x + 0.2188 α5,P -14972x3 + 1011.2x2 - 18.723x + 0.2254 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

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

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)

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

Chamber experiments 52 + 52 = 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)

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

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

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

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

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)

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)

Thank you