Contribution of SOA to Ambient PM 2.5 Organic Carbon in Eastern United States Locations

Transcription

1 Contribution of SOA to Ambient PM 2.5 Organic Carbon in Eastern United States Locations Tadeusz E. Kleindienst 1, Edward O. Edney 1, Michael Lewandowski 1, John H. Offenberg 1, and Mohammed Jaoui 2 1 National Exposure Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina USA 2 Alion Science and Technology, Research Triangle Park, North Carolina USA MANE-VU/Midwest RPO Regional Haze Science Meeting Baltimore, Maryland July 10, 2007

2 Background Condensable material formed from gas-phase reactions of hydrocarbons produce secondary organic aerosol (SOA) that comprises part of the organic carbon (OC) in PM2.5. SOA typically contains organic compounds more highly polar than those from primary emissions and can be semivolatile or nonvolatile. Recent data indicates SOA can be a significant summer component of PM2.5 in the eastern U.S. Laboratory experiments indicate that organic products in field samples can be associated with specific hydrocarbon precursors (Edney et al. Atmos. Environ., 2003). Organic tracer technique for SOA has recently been described (Kleindienst et al., Atmos. Environ., in press)

3 Other Approaches for Evaluating Ambient SOA (SOA/OC) Deficit in chemical mass balance between measured OC and primary organic aerosol (POA) from CMB analysis (Schauer et al., 2002; Zheng et al., 2002) Contribution of SOA to PM 2.5 from OC/EC ratio (Turpin and Huntzicker 1995) Relative contributions of anthropogenic and biogenic HCs to SOA based on a combined 14 C and source-receptor method (e.g. Lewis et al., 2004)

4 Simplified View of Ambient Primary and Secondary Carbon Organic Aerosol Component of PM Secondary Sources Primary Sources Distribution of Source Contributions Changes with Season

5 General Description of SOA from Individual Source SOA component from α-pinene reactions with OH, O 3, NO 3 followed by secondary and higher order aerosol-forming processes Tracer compounds α-p SOA Polar multifunctional oxygenates that may include oligomers and other high molecular-weight compounds

6 Objectives for the Study Find tracer compounds representative of the major SOA precursors from laboratory studies. Identify tracer compounds found both in the laboratory and field. Estimate the mass fraction of tracers to the formed SOA Focus on isoprene, α-pinene, β-caryophyllene, toluene Determine major sources of SOA in PM 2.5 in RTP, NC, Detroit, MI, and other locations using the tracer compounds. What fraction of the OC represented by SOC. Compare biogenic vs. anthropogenic contribution. Examine seasonal dependencies. Compare differences in location using the same analysis.

7 Experimental System for Laboratory Studies Ozone, SO 2 and NO/NO x Analyzers Gas Chromatography - Flame Ionization Detector (GC-FID) Other Sampling Hygrometer SOC Msmt Inlet Manifold Semicontinuous Organic Carbon Measurement NERL Dynamic Photochemical Reaction Simulator Volume = 14.5 m 3 40 L min -1 (τ = 6 h) Scanning Mobility Particle Sizer (SMPS) Filter Sampling Devices for Chamber Aerosol Gas Phase Carbonyl Product Measurements Chemical Composition Mass Measurement Inorganic IC GC-MS Gravimetric Mass Organic SOA Msmt MALDI LC-ESI ESI Experiments conducted in a dynamic mode to operate at relatively low reactant concentrations and to collect sufficient aerosol for analysis. Analyze tracer compounds by GC/ITMS and OA and OC by standard methods.

8 Reactive Systems Contributing to SOA Studied Here Isoprene Photooxidation Role of acid catalysis (H 2 SO 4 acidic seed; in presence of SO 2 ) α-pinene Oxidation Photooxidation Ozone reaction Role of acid catalysis Toluene Photooxidation β-caryophyllene Oxidation Photooxidation Ozone reaction

9 Tracer Compounds from Laboratory Irradiations

10 Tracer Compounds for the Source Categories α-pinene SOA Tracers Pinic acid Pinonic acid 3-Acetyl pentanedioic acid 3-Acetyl hexanedioic acid 3-(2-Hydroxyethyl)-2,2-dimethylcyclobutane carboxylic acid 3-Hydroxyglutaric acid 2-Hydroxy-4-isopropyladipic acid 3-Hydroxy-4,4-dimethylglutaric acid Isoprene SOA Tracers 2-Methylglyceric acid 2-Methylerythritol 2-Methylthreitol Toluene SOA Tracer 2,3-Dihydroxy-4-oxopentanoic acid β-caryophyllene SOA Tracer β-caryophyllinic acid (C 14 H 22 O 4 )

11 Structures for Selected Tracer Compounds α-pinene tracers Pinonic acid Pinic acid HO O OH O A 5 A 6 Isoprene tracers T 3 Toluene tracer A 2 O HO O O OH I 1 β-caryophyllene tracer A 3 I 2 C 1 A 4 HO O O O OH I 3

12 Laboratory Data for Mass Fractions (e.g., α-pinene photooxidation; OM/OC α-p = 1.37 ± 0.15) Experiment ID [hc o ] (ppmc) [NO X,o ] (ppm) [SOA] (μg m -3 ) Σ [tr i ] (μg m -3 ) α-p α-p α-p α-p α-p α-p α-p α-p α-p α-p α-p α-p α-p α-p α-p f soa average f soa, α-p ± average f soc, α-p ± 0.111

13 PM 2.5 Field Measurements Research Triangle Park, NC* Summer 2000, 2001 Baltimore, MD* Summer 2001 Philadelphia, PA (NEOPS)* Summer 2001 New York, NY* Summer 2001 Tampa, FL (BRACE) Summer 2002 Research Triangle Park, NC Entire Year 2003 Detroit, MI (DEARS) Summer 2004, 2005 Detroit, MI (DEARS) Winter * Qualitative measurements with double derivative, PFBHA/BSTFA

14 Example of Tracer Compounds from TIC (Detroit, MI, 24 Aug 2004; OC = 3.72 μg m -3 ) Sum of Tracer Concentrations as KPA I : Isoprene: 168 ng m -3 A: α-pinene: 153 ng m -3 B: β-caryophyllene: 6.8 ng m -3 T : Toluene: 4.4 ng m -3

15 Relative Abundance of Tracer Compounds in RTP, NC 2003

16 Method for Estimating SOC Source Contributions Laboratory measurements Irradiated single component hydrocarbon/no X mixtures; repeat for other conditions Identify tracer compounds and determine concentrations as ketopinic acid Calculate the mass fraction of the tracer compounds to the measured SOC Apply to field measurements Measure SOC tracers in ambient PM 2.5 Apply the mass fraction factor to get the SOC for each precursor type Compare SOC contributions to the measured OC Assumptions and uncertainties Assume mass fraction of the tracers is the same in the field as in the laboratory. Other possible of sources of the tracer compounds currently not known Standard deviation of the mass fraction measurements were on average 35% Extrapolations from single hydrocarbon contributions to compound classes. Measurement of ambient OC and the precursor contribution to OC are independent quantities.

17 Contribution of Isoprene SOC to Ambient OC (Using 2-methylglyceric acid and two 2-methyl tetrols; RTP, NC USA) 8 7 Winter Spring Summer Fall OC isoprene ugc m -3 Julian Date

18 Contribution of Monoterpene SOC to Ambient OC (Nine tracers for α-pinene; RTP, NC USA) Winter Spring Summer Fall OC a-pinene Julian Date ugc m -3

19 Contribution of Sesquiterpene SOC to Ambient OC (Tracer using β-caryophyllinic acid; RTP, NC USA) Winter Spring Summer Fall OC b-caryophyllene Julian Date ugc m -3

20 Contribution of Aromatic SOC to Ambient OC (Tracer using 2,3-dihydroxy-4-oxopentanoic acid; RTP, NC USA) 8 7 Winter Spring Summer Fall OC toluene ugc m -3 Julian Date

21 SOC Contributions to Ambient OC (2003 Research Triangle Park, NC) Winter Spring Summer Fall other toluene b-caryophyllene isoprene a-pinene Julian Date 2003 ug C m -3

22 Bimonthly Contribution of SOC to Ambient OC (2003 Research Triangle Park, NC) OC Contributions (ug/m3) estimated fraction SOC Jan-Feb March-April May-June July-August Sept-Oct Nov-Dec Isoprene a-pinene b-caryophyllene Toluene Other OC Other OC = OC - Isoprene SOA - Aromatic SOA - Monoterpene SOA - Sesquiterpene SOA Other OC includes biomass comb, gasoline exhaust, diesel emissions and meat cooking operations

23 SOC Contributions to Ambient OC (DEARS Ambassador Bridge Site, Detroit, MI, 11 Aug 1 Sep 2004) Avg SOC mass: 1.55 μgc m -3 Avg fraction SOC: Anthrop SOC/Total SOC: 0.13 Organic Carbon (ugc/m3) Sample Isoprene a-pinene b-caryophyllene Toluene Other

24 Summary of Key Points Secondary organic aerosol from isoprene, monoterpenes, sesquiterpenes, and aromatics contributes substantially to organic carbon in PM 2.5 in the eastern U.S. mainly during the summer. Other U.S. areas under study. Aromatic contribution higher than typically predicated in air quality models. Organic carbon in PM 2.5 was found to range from 2 5 μgc m -3 throughout the year with primary sources dominating in the winter and SOC dominating during the summer. Primary and secondary contributions can be offsetting leading to minor seasonal trends. Estimates of SOC contribution from biogenic HC precursors found to be substantially greater than anthropogenic HC precursors in the eastern U.S. Results consistent with SOC contributions to the organic carbon measured in laboratory mixtures and with 14 C data measured in laboratory experiments and from 14 C in field studies.

25 Next Steps Conduct studies combining both CMB analysis for primary compounds and mass fractions for secondary compounds to see the degree of consistency between SOA and other OC from the CMB analysis. Look at alternative double derivative technique to improve sensitivity of tracers from aromatic hydrocarbons. Use information from laboratory and field studies to provide basis for an improved SOA module for CMAQ. Determine tracers compounds from other classes of possible SOA producing hydrocarbons, such as, high MW alkanes, etc. Determine tracer compounds from additional high volume aromatic hydrocarbons (e.g., m-xylene, 1,2,4-TMB) and sesquiterpenes (e.g., α- humulene, α-farnesene). Examine SOA production from complex mixtures. Further study role of acid-catalysis on SOA formation and possible tracer compounds produced.

26 Bibliography Edney et al., 2003, Polar organic oxygenates in PM 2.5 at a southeastern site in the United States, Atmos. Environ. 37, Kleindienst et al., 2004, Determination of secondary organic aerosol products from the photooxidation of toluene and their implications in PM 2.5. J. Atmos. Chem. 47, Jaoui et al, 2004, Identification and quantification of aerosol polar oxygenated compounds bearing carboxylic or hydroxyl groups. 1. Method development. Analyt. Chem. 76, Jaoui et al., 2005, Identification and quantification of aerosol polar oxygenated compounds bearing carboxylic or hydroxyl groups. 2. Organic tracer compounds from monoterpenes, Environ. Sci. Tech. 39, Edney et al., 2005, Formation of 2-methyl tetrols and 2-methylglyceric acid in secondary organic aerosol from laboratory irradiated isoprene/no X /SO 2 /air mixtures and their detection in ambient PM 2.5 samples collected in the eastern United States, Atmos. Environ. 39, Offenberg et al. 2006, Thermal properties of secondary organic aerosols. Geophys. Res. Lett. 33, L03816 Claeys et al. 2007, Hydroxydicarboxylic acids: Markers for secondary organic aerosol from the photooxidation of α- pinene. Environ. Sci. Technol. 41, Jaoui et al., 2007, β-caryophyllinic acid: An atmospheric tracer for β-caryophyllene secondary organic aerosol. Geophys. Res. Lett. 34, L Surratt et al. 2007, Evidence for organosulfates in secondary organic aerosol. Environ. Sci. Technol. 41, Lewandowski et al., 2007, Composition of PM 2.5 during the summer of 2003 in Research Triangle Park, North Carolina. Atmos. Environ. 47, Offenberg et al. 2007, Contributions of toluene and α-pinene to SOA formed in an irradiated toluene/α-pinene/no X /air mixture: Comparison of results using 14 C content and SOA organic tracer methods. Env. Sci. Technol. 41, Kleindienst et al., 2007, Estimates of the contribution of biogenic and anthropogenic hydrocarbons to secondary organic aerosol at a Southeastern U.S. Location, Atmos. Environ. (in press).

27 Disclaimer Although this work was reviewed by U.S. EPA and approved for publication, it may not necessarily reflect official Agency policy.