An aromatic hydrocarbon study with an extended SAPRC99 mechanism of the CMAQ system: Application for the Houston-Galveston area

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1 An aromatic hydrocarbon study with an extended SAPRC99 mechanism of the CMAQ system: Application for the Houston-Galveston area Violeta F. Coarfa, Daewon W. Byun Institute for Multidimensional Air Quality Studies (IMAQS), University of Houston 4 th Annual Community Modeling and Analysis System Center Models-3 Users Conference September, 2005

2 Aromatic hydrocarbons Significant fractions of the reactive hydrocarbons in urban areas Rated among the most important classes of compounds with regard to the formation of photo-oxidants in the lower atmosphere Responsible for about 35% of the anthropogenic ozone formation; their contribution to the total non-methane hydrocarbon (NMHC) emissions was calculated to be 30%, being the second major contributor to the NMHCs ( Chemical processes in atmospheric oxidation, Georges Le Bras) Toluene was measured the most abundant aromatic component in urban air (Jeffries, 1995)

3 Why study aromatics? Aromatics are toxic substances with serious impact on the human health Benzene known human carcinogen Many aromatics, such as benzene, toluene and xylene (BTX), are currently listed as Mobile Source Air Toxics (MSATs) (EPA); aromatics from motor vehicles are potent ozone formers ; they also photochemically react in the atmosphere to produce fine particulate aerosols and dealkylate in the exhaust to yield cancerforming benzene. Study goals: To better understand their impact on the human health and the air quality To protect the public health by limiting their emissions from the man-made sources To help communities prepare to better respond in case of chemical spills of such substances Air toxics assessment activities: - assessment of the emissions: monitoring and measuring air quality, modeling - development and implementation of control strategies of their emissions; - emergency response in case of serious events.

4 Emission distribution based on source category for Harris county (Houston) NEI99 (HAPs) BENZENE - Harris county Toluene - Harris county 16% 7% 1% 24% np acr_nr 8% 17% 0% np acr_nr nr on 17% nr on 52% pt 58% pt Source category legend: np nonpoint acr_nr aircraft nr- nonroad on onroad pt point Ethyl-benzene - Harris county 15% 11% 0% np acr_nr Mobile sources (onroad+nonroad): important emission sources for the aromatic hydrocarbons 39% 35% nr on pt

Clinton site observational data (2000) analysis - hourly observational Clinton data for 2000 year - comparison of atmospheric concentration among different aromatic species at Clinton site 1 2 3 4 5

5 Clinton site observational data (2000) analysis - hourly observational Clinton data for 2000 year - comparison of atmospheric concentration among different aromatic species at Clinton site log (conc) (ppbv) species ID Annual average concentration of aromatic hydrocarbons at Clinton site (2000) conc (ppbv) Jan Feb March April May June July Aug Sep Oct Nov Dec benzene toluene p,m-xylenes Monthly variation of toluene, benzene and m,p- xylene concentrations at Clinton site (2000)

6 Maximum incremental reactivity (MIR) for aromatic hydrocarbons Compound MIR Compound MIR (grams O3/grams VOC) (grams O3/grams VOC) Nitrobenzene Toluene 3.97 P-dichlorobenzene 0.20 P-xylene 4.24 Chlorobenzene 0.36 Methylnaphthalene 4.61 Benzene 0.81 di- methylnaphthalene 5.54 Sec-butylbenzene TMB 7.18 N-propylbenzene 2.20 O-xylene 7.48 Iso-propylbenzene 2.32 M-xylene Ethylbenzene TMB Naphthalene TMB MIR - reactivity of a volatile organic compound (VOC) under atmospheric conditions, where an amount of that VOC has the greatest impact on ozone formation. Source: VOC reactivity data as of February, 5, 2003, William P.L. Carter

Aldine site Clinton site MIR reactivity = MIR x

Clinton sites Source - Estes, Mark et al:

7 Aldine site Clinton site MIR reactivity = MIR x [conc VOC (ppbv)] x [MW VOC /MW Ozone ] biggest contributions to the MIRs came from: xylenes, toluene, trimethylbenzenes for the Aldine and Clinton sites Source - Estes, Mark et al: Reactivity of VOCs measured by automated gas chromatography in Houston,

8 Chemistry of aromatic hydrocarbons Atmospherics oxidation of aromatics -> chamber studies Reactants of aromatic hydrocarbons: O 3, O 3 P, OH, NO 3 Reactions with OH radical -> always important for aromatics; Reactions with O 3 -> important just for aromatic alkenes; Reactions with NO 3 -> important just for aromatic alkenes and phenols, at night; Reactions with O 3 P -> less important in the troposphere;

9 Reaction with OH radical Reaction with OH - quite complicated, and still not fully understood. Main decay process of aromatics; considered in SAPRC99 chemical mechanism OH radical reacts by addition to one of the aromatic ring double bonds (~ 90%). Many of the oxidation products are the result of breaking the ring structure.

10 How aromatics lead to ozone formation? Aromatics + HO -> peroxy radicals + other products NO + peroxy radicals -> NO 2 NO 2 + hν -> NO + O( 3 P) O( 3 P) + O 2 -> ozone

11 Aromatic hydrocarbon reaction scheme TOLUENE main source - Jack G. Calvert et al.: The Mechanisms of atmospheric oxidation of aromatic hydrocarbons, Oxford University Press, 2002

12 Motivation for refining the aromatic hydrocarbon representation in SAPRC99 Currently, in the SAPRC99 chemical mechanism of CMAQ system, the aromatic hydrocarbons are represented by two lumped species, ARO1 and ARO2: a. ARO1 - aromatics with K OH < 2x10 4 ppm -1 min -1 b. ARO2 - aromatics with K OH > 2x10 4 ppm -1 min -1 ARO1 + HO = 0.224*HO *RO2_R *RO2_N *PROD *GLY *MGLY *PHEN *CRES *DCB *DCB3 ARO2 + HO = 0.187*HO *RO2_R *RO2_N *GLY *MGLY *CRES *DCB *DCB *DCB3 To more accurately analyze the impact of such hydrocarbons on ozone formation and study the physical and chemical properties of such aromatics, we extend the SAPRC99 mechanism so that it explicitly represents several aromatic hydrocarbon species emitted into the atmosphere in significant amounts.

13 Aromatic hydrocarbon reactions in SAPRC99 mechanism - oxidation products and the corresponding model species in SAPRC99 - Aromatics + OH Addition to the ring 90% H-abstraction 10% - phenol -type, cresol -type: PHEN, CRES - aromatic aldehydes: BALD - aromatic ketones: PROD2 - α-dicarbonyl ketones: BACL - glyoxal: GLY - alkyl-glyoxal: MGLY - other products, such as DCB1, DCB2, DCB3 unsaturated dicarbonyl compounds VERY REACTIVE the oxidation products, especially the 1,4-unsaturated carbonyls: toxics or possible toxics with both carcinogenic and mutagenic properties

14 Aromatic species included in the SAPRC99 mechanism new chemical mechanism SAPRC99_ARO - extracted from ARO1 lumped species: 1. benzene 5. iso-propylbenzene 2. toluene 6. N-propylbenzene 3. ethylbenzene 7. p-dichloro-benzene 4. chlorobenzene 8. nitrobenzene 9. sec-butyl-benzene - extracted from ARO2 lumped species: 1. O-xylene 5. 1,2,4-trimethylbenzene 2. M-xylene 6. 1,3,5-trimethylbenzene 3. P-xylene 7. naphthalene 4. 1,2,3-trimethylbenzene 8. methylnaphthalene 9. dimethylnaphthalene

15 OH radical reaction constants at 300K for aromatics in the SAPRC99_ARO chemical mechanism. Source - Carter, W.P.L.: Documentation of the SAPRC99 chemical mechanism for VOC reactivity assessment, May8, 2000

16 Methodology of refining SAPRC99 - SMOKE processing input files (W.P.L. Carter s software: ProfPro and SpecPro programs) - CMAQ input files (W.P.L. Carter s software: MechPro and EmitSum programs, CMAQ mechanism compiler) (Source W.P.L. Carter: Development of chemical speciation database and software for processing VOC emissions, June 09, 2004) - EBI program (EPA) to create a new EBI solver that accounts for the new aromatic species - SMOKE1.4, CMAQ4.4 simulations: comparison of the simulation results with the observational data

17 Simulation details Inventory NEI99 (final version 3) Modeling domain: 4km_83x65 Modeling episode: 22 Aug 01 Sept, 2000 SMOKE2.1 CMAQ4.4

Smoke2.1 results ARO1 and ARO2 case 12 12 ARO1_SAPRC99.

moles/hour SAPRC99reg: ARO1 contains only 0.295 benzene (0.

18 Smoke2.1 results ARO1 and ARO2 case ARO1_SAPRC99.ARO ARO1_SAPRC99 22 August - 01 September, 2000 emissions in moles/hour SAPRC99reg: ARO1 contains only benzene (0.705 is inert) SAPRC99_ARO: BENZ contains benzene ARO1_SAPRC99.ARO ARO1_SAPRC99 22 August - 01 September, 2000 emissions in moles/hour

19 CMAQ4.4 simulation results ozone comparison

20 Ozone simulated concentration comparison with observational data at CAMs sites Q15: CB4, TEI base5b psito2n2 Q60: SAPRC99, NEI99fv3 Q61: SAPRC99_ARO, NEI99fv3

21 Ozone simulated concentration comparison with observational data at super sites

22 Formaldehyde simulated concentration comparison with observational data

23 SMOKE2.1 results for toluene and ethylbenzene

24 CMAQ4.4 results for aromatics August 25, 1 pm GMT and 9 pm GMT

25 Comparison of CMAQ4.4 simulated concentrations with observational data Surface measurement data sets Clinton, La Porte Aircraft measurement data sets: Baylor, NOAA

26 Comparison with observational data Clinton site BENZENE simulation observational Clinton conc (ppbv) 8/21 8/22 8/23 8/24 8/25 8/26 8/27 8/28 8/29 8/30 8/ ETHYLBENZENE observational Clinton simulation conc (ppbv) 8/21 8/22 8/23 8/24 8/25 8/26 8/27 8/28 8/29 8/30 8/31

27 8/30 8/31 8/29 8/ TOLUENE observational Clinton simulation 8/26 8/27 O-XYLENE 8/25 8/24 8/23 8/ observational Clinton simulation 8/30 8/31 8/29 8/28 8/26 8/27 8/25 8/24 8/23 8/22 conc (ppbv) conc (ppbv)

28 P+M-XYLENES /22 8/23 8/24 8/25 8/26 8/27 8/28 8/29 8/30 8/31 conc (ppbv) simulation observational Clinton O-XYLENE /22 8/23 8/24 8/25 8/26 8/27 8/28 8/29 8/30 8/31 conc (ppbv) observational Clinton simulation

29 8/29 8/30 8/31 8/ TMB 8/26 8/ TMB simulation observational Clinton 8/25 8/24 8/23 conc (ppbv) 8/21 8/ observational Clinton simulation 8/29 8/30 8/31 8/28 8/26 8/27 8/25 8/24 8/23 conc (ppbv) 8/21 8/22

30 N-PROPYLBENZENE /21 8/22 8/23 8/24 8/25 8/26 8/27 8/28 8/29 8/30 8/31 conc (ppbv) observational Clinton simulation ISO-PROPYLBENZENE /21 8/22 8/23 8/24 8/25 8/26 8/27 8/28 8/29 8/30 8/31 conc (ppbv) observational Clinton simulation

31 Comparison with observational data La Porte site 6.00 Toluene La Porte site simulation observational 5.00 conc (ppbv) /22 8/23 8/24 8/25 day 8/26 8/29 8/30 8/31

32 Comparison with observational data aircraft NOAA data Ethyl-benzene NOAA data conc (ppbv) observation simulation 0 25-Aug 27-Aug 28-Aug 30-Aug BENZENE NOAA data conc (ppbv) observation simulation 0 25-Aug 27-Aug 28-Aug 30-Aug

33 Comparison with observational data aircraft Baylor data Benzene Baylor aircraft data conc (ppbv) simulation observation 0 8/22 8/25 8/26 8/29 8/30 Toluene baylor data conc (ppbv) Aug 25-Aug 26-Aug 29-Aug 30-Aug observation simulation

34 Process analysis in CMAQ work in progress CMAQ predicts the spatial and temporal distributions of pollutants using a solving system of differential equations ( chemical solvers) cumulative effect of all chemical and physical processes (chemical reactions, emissions, diffusion, advection). Process analysis: IRR and IPR - tools that help us quantify the impact of different physical/chemical processes on model predictions; - IPR = Integrated Process Rate Analysis effects of all physical and net effect of chemistry on model simulated concentrations - IRR = Integrated Reaction Rate Analysis effects of the chemical transformations on model predicted concentrations SAPRC99_ARO mechanism gives us the possibility to make the PA study for different aromatics and understand their physical and chemical processes

35 IPR preliminary results with SAPRC99_ARO for Toluene Impact of each physical and net chemical processes on predicted modeled concentrations

36 IRR preliminary results with SAPRC99_ARO HO2 radical production - which aromatic species have big impact on ozone formation on HGA?

37 Conclusions For the Houston-Galveston area, where mobile sources are important emissions sources for aromatic species, the new chemical mechanism, SAPRC99_ARO gives us a better chemical resolution to study certain aromatic compounds, such as benzene, toluene, xylene isomers (BTX), known as mobile source air toxics; There are ozone differences between SAPRC99_ARO and regular SAPRC99 (max absolute difference = 9 ppbv) caused by aromatic emission differences; Comparisons of the simulated aromatic species concentrations with observational data showed a good agreement for some of the analyzed species; however a better inventory for HGA (Texas Emission Inventory) will be used for new simulations with SAPRC99_ARO; SAPRC99_ARO gives the possibility to study the effect of physical and net chemical processes on predicted model concentrations, as well as to understand the chemical transformations for the aromatic species included in the new mechanism and their impact on ozone formation.

38 Acknowledgments Dr. William.P.L. Carter, University California, Riverside, CA Dr. Soontae Kim, IMAQS, University of Houston, TX emissions preprocessing Ms. Fang Yi, IMAQS, University of Houston, TX meteorology

J1.7 IMPACT OF THE ON-ROAD AND MOBILE SOURCES ON THE BENZENE AND TOLUENE EMISSIONS AND CONCENTRATIONS IN THE HOUSTON-GALVESTON AREA

J1.7 IMPACT OF THE ON-ROAD AND MOBILE SOURCES ON THE BENZENE AND TOLUENE EMISSIONS AND CONCENTRATIONS IN THE HOUSTON-GALVESTON AREA J. IMPACT OF THE ON-ROAD AND MOBILE SOURCES ON THE BENZENE AND TOLUENE EMISSIONS AND CONCENTRATIONS IN THE HOUSTON-GALVESTON AREA Violeta F. Coarfa*, Daewon W. Byun Institute for Multidimensional Air Quality