SOA Model by Partitioning and Heterogeneous Reactions in the Presence of Inorganic Species

1. SOA Model by Partitioning and Heterogeneous Reactions in the Presence of Inorganic Species Myoseon Jang1, Gang Cao2, Amanda Northcross2 November 20, 2007 1 Department of Environmental Engineering Sciences, University of Florida, Gainesville, Florida, USA. 2 Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, NC, USA. Today I am going to talk about Secondary Organic Aerosol Production by Heterogeneous Acid-Catalyzed Reactions.Today I am going to talk about Secondary Organic Aerosol Production by Heterogeneous Acid-Catalyzed Reactions.

2. Overview I. Background SOA formation Heterogeneous reactions in acidic aerosols. II. New SOA Model III. Evaluation of new SOA model using chamber data This is the overview of today’s presentation. I will simply introduce 1and 2. Most of presentation will be focused on 3. This is the overview of today’s presentation. I will simply introduce 1and 2. Most of presentation will be focused on 3.

3. Before going to detail of heterogeneous chemistry of organic and inorganic acid, let us see the structure of the current PM2.5 module in CMAQ as a regional model. There are inorganic aerosol module and OC module. These two model is separately setup without any interaction. For example, Inorganic aerosol formation include inorganic thermodynamics. OC has two part. The primary organic carbon linked to source based model and secondary organic model. However, inorganic and organic Before going to detail of heterogeneous chemistry of organic and inorganic acid, let us see the structure of the current PM2.5 module in CMAQ as a regional model. There are inorganic aerosol module and OC module. These two model is separately setup without any interaction. For example, Inorganic aerosol formation include inorganic thermodynamics. OC has two part. The primary organic carbon linked to source based model and secondary organic model. However, inorganic and organic

4. Secondary Organic Aerosol Formation SOA is a major component of atmospheric organic carbon. SAO mass ranges from 20-90% of total organic carbon. Here is atmospheric particle reactor and its main recipes. VOCs from biogenic and aromatics react 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. SOA is a major component of atmospheric organic carbon. SAO mass ranges from 20-90% of total organic carbon. Here is atmospheric particle reactor and its main recipes. VOCs from biogenic and aromatics react 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.

5. I will shows possible reaction mechanisms of carbonyl species. This looks complex but there are two key information. 1. The carbonyl reaction is accelerated in the presence of an acid catalyst. 2. Secondly particle phase heterogeneous reactions produce high MW products which have low volatility. Aldehyde can be hydrated in the particle phase and this hydrate form of carbonyls also reacted with more carbonyl again and undergo polymerization. Such a reaction chain could lead to long chain polymers. Aldol condensation is also another way to increase molecular weight. Another important reaction pathway is the reaction of organics with sulfuric acid forming organic sulfate. 3. Notice the functional group transformation from carbonyl double bond to C-O-C bond. I will shows possible reaction mechanisms of carbonyl species. This looks complex but there are two key information. 1. The carbonyl reaction is accelerated in the presence of an acid catalyst. 2. Secondly particle phase heterogeneous reactions produce high MW products which have low volatility. Aldehyde can be hydrated in the particle phase and this hydrate form of carbonyls also reacted with more carbonyl again and undergo polymerization. Such a reaction chain could lead to long chain polymers. Aldol condensation is also another way to increase molecular weight. Another important reaction pathway is the reaction of organics with sulfuric acid forming organic sulfate. 3. Notice the functional group transformation from carbonyl double bond to C-O-C bond.

7. Next, heterogeneous aerosol formation was proved to biogenic SOA. Isoprene or acrolein was reacted with ozone in the presence of acidic aerosol. Notice higher yields in the presence of acid catalyst than neutral seed. (The SOA yields were normalized by ozone and initial VOC concentrations)Next, heterogeneous aerosol formation was proved to biogenic SOA. Isoprene or acrolein was reacted with ozone in the presence of acidic aerosol. Notice higher yields in the presence of acid catalyst than neutral seed. (The SOA yields were normalized by ozone and initial VOC concentrations)

8. SOA from ozonolysis of various monoterpenes The same trend has been observed for biogenic terpenes showing higher aerosol yields in the presence of acidic aerosol seeded with sulfuric acid. The same trend has been observed for biogenic terpenes showing higher aerosol yields in the presence of acidic aerosol seeded with sulfuric acid.

9. No exception has found in Aromatic aerosol. In general, aromatic VOC is categorized into two classes. High and low SOA yield aromatic. Lee methyl substituted aromatic VOC such as toluene is in the category of high SOA yield and more methyl substituted such as trimethyl benzene is in lower SOA yield aromatics. SOA yields higher with acidic aerosol in both toluene and TMB. Overall, Photoirradiation reduces the SOA yields and also alters effects of acidity depending upon the aromatic system. No exception has found in Aromatic aerosol. In general, aromatic VOC is categorized into two classes. High and low SOA yield aromatic. Lee methyl substituted aromatic VOC such as toluene is in the category of high SOA yield and more methyl substituted such as trimethyl benzene is in lower SOA yield aromatics. SOA yields higher with acidic aerosol in both toluene and TMB. Overall, Photoirradiation reduces the SOA yields and also alters effects of acidity depending upon the aromatic system.

10. Effect of %RH on SOA yield Particle acidity effects is strongly related to humidity and inorganic seed composition. For example, SOA yield is higher at lower humidity and with higher sulfuric acid fraction in inorganic seed aerosol.Particle acidity effects is strongly related to humidity and inorganic seed composition. For example, SOA yield is higher at lower humidity and with higher sulfuric acid fraction in inorganic seed aerosol.

11. II. SOA Model

12. Gas Phase Reaction and Products explicit chemical mechanisms for product distribution: e.g. ?-pinene using Master Chemical Mechanism (MCM) and UNC mechanisms chemical solver to execute mechanisms: MORPHO by Jeffries et al. Application of ?-pinene kinetics to other terpenes (e.g. d-limonene and terpinolene) based on MCM protocol The gas phase concentration is estimated using MCM the master chemical mechanism A series of differential equations represents each reaction within the mechanism MORPHO a chemical solver will be used to compile and solve the equations given inputs of temperature, time, Initial ozone and terpene concentration MCM produces a nearly explicit product distribution Each terpene will have a model created for the ozonolysis rxns “A fundamental assumption in its construction, therefore, is that the kinetics and products of a large number of unstudied chemical reactions can be defined on the basis of the known reactions of a comparatively small number of similar chemical species, by analogy and with the use of structure-reactivity correlations.” (Saunders et al. 2003a). The gas phase concentration is estimated using MCM the master chemical mechanism A series of differential equations represents each reaction within the mechanism MORPHO a chemical solver will be used to compile and solve the equations given inputs of temperature, time, Initial ozone and terpene concentration MCM produces a nearly explicit product distribution Each terpene will have a model created for the ozonolysis rxns “A fundamental assumption in its construction, therefore, is that the kinetics and products of a large number of unstudied chemical reactions can be defined on the basis of the known reactions of a comparatively small number of similar chemical species, by analogy and with the use of structure-reactivity correlations.” (Saunders et al. 2003a).

13. SOA formation: Precursor volatile hydrocarbons Biogenic hydrocarbons: chemical species from vegetation. Anthropogenic hydrocarbons: Aromatics and long chain alkanes

14. SOA major products from the ozone reaction of ?-pinene Ozonolysis of a-Pinene produce various oxidation products. Most of products has aldehyde, alcohol, carboxylic acid in their molecular structure. What we learn is these oxygenated products are much less volatile compared to original terpenes. Ozonolysis of a-Pinene produce various oxidation products. Most of products has aldehyde, alcohol, carboxylic acid in their molecular structure. What we learn is these oxygenated products are much less volatile compared to original terpenes.

15. SOA products from Toluene/NOx/Sun-light Using outdoor chamber, toluene was photo-irradiated in the presence of NOx. The multifunctional carbonyls such as conjugated carbonyls and bicarbonyl was identified using GC-ion trap associated with various derivatization method. These products are potentially highly reacted and further transformed to higher molecular products in the aerosol phase.Using outdoor chamber, toluene was photo-irradiated in the presence of NOx. The multifunctional carbonyls such as conjugated carbonyls and bicarbonyl was identified using GC-ion trap associated with various derivatization method. These products are potentially highly reacted and further transformed to higher molecular products in the aerosol phase.

17. This is the example of lumping and associated stoichiometic coefficients for the a-pinene ozonolysis system. This is the example of lumping and associated stoichiometic coefficients for the a-pinene ozonolysis system.

18. Stoichiometric Coefficients for Product Groups

19. II. SOA Model

20. Semiempirical models for kinetics of carbonyl reactions in acidic aerosol Now What we need is estimation of heterogeneous aerosol formation. We have built up the semiempirical model for kinetics of carbonyl reaction in the aerosol phase. 1 The rate constant consists of environmental parameters associated with particle acidity and molecular structure information. 3. We are implementing a lumping method to categorize the molecular structure for diverse secondary organic products. Now What we need is estimation of heterogeneous aerosol formation. We have built up the semiempirical model for kinetics of carbonyl reaction in the aerosol phase. 1 The rate constant consists of environmental parameters associated with particle acidity and molecular structure information. 3. We are implementing a lumping method to categorize the molecular structure for diverse secondary organic products.

21. observed OM vs. OM predicted by a partitioning In the early state, we have develop the semiempirical model for heterogeneous organic aerosol formation using various simple model carbonyls. This example shows how the semiempirical model is feasible to predict the heterogeneous aerosol productions. Organic aerosol growth of diverse carbonyls has been observed in diverse environments such as different humidity and compositions. The aerosol growth predicted by partitioning did not the predictive power. However, you can see the remarkable improvement for prediction power for aerosol growth when the semi-empirical model is implemented. In the early state, we have develop the semiempirical model for heterogeneous organic aerosol formation using various simple model carbonyls. This example shows how the semiempirical model is feasible to predict the heterogeneous aerosol productions. Organic aerosol growth of diverse carbonyls has been observed in diverse environments such as different humidity and compositions. The aerosol growth predicted by partitioning did not the predictive power. However, you can see the remarkable improvement for prediction power for aerosol growth when the semi-empirical model is implemented.

22. Log kH-j = x2X + z2log (aw CH+) + r2 pKBH+ + s2I + c2 Based on rate constants of heterogeneous reactions, stoichiometic coefficients of lumping species, consumption of VOC, we can estimate heterogeneous aerosol production using 2nd order reaction rate. Based on rate constants of heterogeneous reactions, stoichiometic coefficients of lumping species, consumption of VOC, we can estimate heterogeneous aerosol production using 2nd order reaction rate.

23. Once the SOA mass is predicted by the heterogeneous reaction model, this OMh is can be feedbacked to the regional model to estimate OMp based on mass balance. Once the SOA mass is predicted by the heterogeneous reaction model, this OMh is can be feedbacked to the regional model to estimate OMp based on mass balance.

25. Terpene and Ozone Decay Results

26. Time profile of aerosol yields in acidic and neutral aerosols The model developed using from maximum aerosol mass in the indoor chamber has been extended to the time profile of SOA formation prediction. As you see in this figure, OMH aerosol yield is high at the initial stage which OMP increases with time as OM increases. We can see that the model predicted OMh reasonable agree with experimental OMh time profile. The model developed using from maximum aerosol mass in the indoor chamber has been extended to the time profile of SOA formation prediction. As you see in this figure, OMH aerosol yield is high at the initial stage which OMP increases with time as OM increases. We can see that the model predicted OMh reasonable agree with experimental OMh time profile.

27. The predicted OMH at different Mseed levels (%RH = 20), Fs (%RH = 20), and %RH These are example of model simulation for the OMH. Aerosol mass was simulated for different acidic seed mass, different composition, and humidity.These are example of model simulation for the OMH. Aerosol mass was simulated for different acidic seed mass, different composition, and humidity.

29. Extrapolation of the model from high-medium acidity to weak acidic and neutral systems The model has been extended to weak and neutral aerosol systems which are more relevant to ambient aerosol. This shows how much fraction of OMH is present in total SOA mass. The model has been extended to weak and neutral aerosol systems which are more relevant to ambient aerosol. This shows how much fraction of OMH is present in total SOA mass.

30. Simulation of heterogeneous SOA formation in the ambient condition The model can be applied to the realistic ambient SOA formation. With 10 ug of inorganics, SOA mass by heterogeneous reaction was predicted and also compared to neutral system. Notice that about 3 ug of SOA mass is from heterogeneous reactions.. This aerosol mass can fill the missing SOA mass in the regional model. The model can be applied to the realistic ambient SOA formation. With 10 ug of inorganics, SOA mass by heterogeneous reaction was predicted and also compared to neutral system. Notice that about 3 ug of SOA mass is from heterogeneous reactions.. This aerosol mass can fill the missing SOA mass in the regional model.

31. I will briefly explain the structure of SOA model including both partitioning and heterogeneous reactions. The SOA Model comprises the gas phase kinetics of precursor VOCs producing gas phase product. The resulting gas phase products are lump by stoichiometic coefficients considering partitioning and the tendency in heterogeneous reactions. Aerosol mass by heterogeneous reactions of organics is predicted by a sub model for the reaction rate in the particle phase. Total SOA mass is estimated by the sum of OMp by partitioning and the OMH by heterogeneous reaction. I will briefly explain the structure of SOA model including both partitioning and heterogeneous reactions. The SOA Model comprises the gas phase kinetics of precursor VOCs producing gas phase product. The resulting gas phase products are lump by stoichiometic coefficients considering partitioning and the tendency in heterogeneous reactions. Aerosol mass by heterogeneous reactions of organics is predicted by a sub model for the reaction rate in the particle phase. Total SOA mass is estimated by the sum of OMp by partitioning and the OMH by heterogeneous reaction.

32. Future Work Study SOA in the presence of inorganic aerosols such as salts containing Na, Cl, NH4, SO4 Understand effects of mixtures of different VOCs Heterogeneous SOA production in the presence of acidic seed and NOx Study SOA heterogeneous production in the presence of SO2 Study effect of nitric acid on SOA production Include heterogeneous SOA production to a regional SOA model Non-destructive analytical method for the bulk aerosol Find more evidence of acid effects on SOA formation in field studies

33. Ph.D. Students? Gang Cao (Ph.D. student) ? aromatics? Chunhao Xu (Ph.D student) ? SO2 /SOA? Amanda Northcross ( Ph.D. student)? diverse terpenes ? Dr Nadine Czoschke (05/2006) ? ?-pinene ? Dr. Sangdon Lee (2004) ? effects of indigenous soot particle acidity Acknowledgements Grant from the Atmospheric Chemistry of National Science Foundation (ATM-0314128 and ATM-0703914). Nano-Grant from National Science Foundation (NER-0508247) Start up funding from U. Florida US Environmental Protection Agent Star program One atmosphere project (US Environmental Protection Agent) This research has been supported by NSF and on atmospheric projects. These are the students who have been involved for the heterogeneous aerosol products. Nadine is working on acid catalyst effects on a-pinene aerosol yield. Amanda is working on the mixture of aromatic systems. Sang worked on indigenous acid effects on SOA formation in the soot particles. Gang is working on the aromatic terpeneThis research has been supported by NSF and on atmospheric projects. These are the students who have been involved for the heterogeneous aerosol products. Nadine is working on acid catalyst effects on a-pinene aerosol yield. Amanda is working on the mixture of aromatic systems. Sang worked on indigenous acid effects on SOA formation in the soot particles. Gang is working on the aromatic terpene

36. Chamber experiment This is fundamental components for SOA experiments in the chamber. Chamber is equipped with gas injection system, gas monitoring instruments, particle measurement, and various sampling systems linked to SOA characterization using various thermal, optical, spectroscopic analysis and mass spectrum. Initially the seed particle is injected to the chamber. Then ozone is generated by an ozone generator. The reaction is initiated with injection of precursor VOCs such as terpene into the chamber. The gas phase reaction was progressed by ozone reaction and generate SOA on preexisting particles. This is fundamental components for SOA experiments in the chamber. Chamber is equipped with gas injection system, gas monitoring instruments, particle measurement, and various sampling systems linked to SOA characterization using various thermal, optical, spectroscopic analysis and mass spectrum. Initially the seed particle is injected to the chamber. Then ozone is generated by an ozone generator. The reaction is initiated with injection of precursor VOCs such as terpene into the chamber. The gas phase reaction was progressed by ozone reaction and generate SOA on preexisting particles.

37. Partitioning of inert organic products