Template Assessment of the Sources of Organic Carbon at Monitoring Sites in the Southeastern United States using Receptor and Deterministic Models Ralph Morris and Jaegun Jung, ENVIRON Intl. Corp. Eric Fujita, Desert Research Institute Patricia Brewer, National Park Service 2009 CMAS Conference October 19-21, 2009 Chapel Hill, North Carolina

CMAS Organic Carbon Mass (OCM) is an Important Component of Total PM 2.5 Mass and Visibility Impairment in the Southeastern U.S. Time series of annual PM 2.5 at Great Smoky Mountains NP OCM second highest PM 2.5 component to Ammonium Sulfate

CMAS Projected Improvements in PM 2.5 Mass and Visibility Impairment in Southeastern U.S. primarily due to Reductions in Ammonium Sulfate Estimated percent change in particle extinction from to 2018 for Worst 20% days at VISTAS Class I areas

CMAS VISTAS Organic Carbon Source Apportionment Study Visibility Improvement State and Tribal Association of the Southeast (VISTAS) undertook a multi-pronged study to understand the source of OCM in the southeastern U.S. –Enhanced PM monitoring at 5 sites  Organic Tracers  14 C dating –Receptor OCM/EC source apportionment modeling  Chemical Mass Balance (CMB) and PMF –Deterministic OCM/EC source apportionment modeling  Particulate Source Apportionment Technology (PSAT) in CAMx

CMAS VISTAS OCM Source Apportionment Study Total Carbon (TC) consists of OCM and EC –Most of TC is OCM –Primary emitted and secondarily formed in the atmosphere (SOA) –Anthropogenic and biogenic sources –Past CMB studies identified three largest components as:  Vegetative Burning  Mobile Sources  Unexplained Carbon –Unexplained Carbon presumed to be secondary in origin –Large seasonal and spatial variability in the TC Five monitoring sites with enhanced measurements –4 Class I areas plus Raleigh, NC (Millbrook)

CMAS VISTAS TC Source Apportionment Modeling CMB Receptor TC SA Modeling for 2004/2005 (Fujita et al., 2009): –Gasoline Vehicle Exhaust –Diesel Vehicle Exhaust –Hardwood Combustion –Softwood Combustion –Meat Cooking –Vegetative Detritus –Unexplained Carbon (UC) CAMx/PSAT TC SA Modeling for 2002 (Morris et al., 2009): –Gasoline Combustion –Diesel Combustion –Biomass Burning –Other Point Sources –Other Area Sources –Anthropogenic SOA (SOAA) –Biogenic SOA (SOAB)

CMAS CAMx PSAT TC Source Apportionment Modeling TC Source Apportionment SMOKE emissions modeling to separate TC source categories CAMx photochemical grid model Particulate Source Apportionment Technology (PSAT) to obtain TC source contributions for primary EC and OCM emissions Standard model output to obtain SOAA and SOAB contributions Model performance evaluation VISTAS km Continental U.S. Database –CMAQ and CAMx

CMAS Model Performance Evaluation for OCM –Monthly Fractional Bias (FB) for OCM shows large underprediction bias –OCM underprediction bias greatest for urban-oriented STN network and during summer –Identification of the source of OCM underprediction bias one of objectives of VISTAS TC source apportionment study

CMAS Comparison of CMB & PSAT TC Apportionment Convert CAMx/PSAT OCM into OC using source- specific OCM/OC ratios –e.g., 1.4 for gasoline and 2.2 for SOA Combined OC with EC to make TC Compare seasonal average PSAT & CMB TC Map PSAT and CMB source categories: CMB UC split between modern (UC m ) and fossil (UC f ) Carbon using 14 C data

CMAS TC Gasoline Contributions, CMB vs. PSAT for Winter and Summer –PSAT gasoline contributions much lower than CMB –Variability in PSAT 24-hour gasoline TC contributions shown –Largest difference at suburban MILL site –CMB gasoline TC ~5 times greater than PSAT Gasoline Winter Gasoline Summer

CMAS TC Diesel Contributions, CMB vs. PSAT for Winter and Summer –PSAT seasonal average always lower than CMB –PSAT 24-hour variability overlaps with CMB goodness of fit –On average CMB Diesel TC contributions factor of ~2 greater than PSAT Diesel Winter Diesel Summer

CMAS TC Vegetative Burning Contributions, CMB vs. PSAT Winter and Summer –Comparable seasonal average TC contributions from fires –Lots of variability in the 24- hour PSAT Vegetative Burning TC contributions Fires Winter

CMAS Modern vs. Fossil TC comparisons: 14 C vs. CMB vs. PSAT for Mammoth Cave, KY –CMB and PSAT frequently overstating the fraction of Fossil Carbon –CMB best fit with 14 C data if assume UC is modern (i.e., SOAB)

CMAS CMB vs. PSAT TC Apportionment Comparisons Gasoline: CMB TC ~5 times greater than PSAT Diesel: CMB TC ~2 times greater than PSAT Fires: CMB and PSAT TC comparable Other Area: CMB and PSAT comparable Other Point: No comparable source category in CMB Both CMB w/ 14 C and PSAT estimate that SOA is dominated by SOAB –Exception is suburban Millbrook site that has some higher SOAA Several confounding aspects to the comparison: –CMB frequently overstates amount of fossil carbon –36 km grid cell size in CAMx PSAT diluting TC signal at MILL –PSAT point source has no counterpart in CMB  Maybe partially embedded in gasoline or diesel CMB contributions

CMAS Summary CMB vs. PSAT TC Contributions 5-Site and 4-Site average CMB vs. PSAT TC contributions –Why CMB gasoline (~5x) and diesel (~2x) greater than CAMx/PSAT? –Why CMB/ 14 C SOAB (~1.5-2x) greater than CAMx/PSAT? –Why does CMB not attribute TC to stationary sources (points)?

CMAS Gasoline/Diesel TC Contributions CAMx/PSAT gasoline and diesel TC emissions –MOBILE6 on-road mobile sources  LDGV dominate gasoline  HDDT large component of diesel –NONROAD non-road mobile source emissions  Large component of diesel  Locomotive, marine vessels and airplanes separately EPA’s MOBILE6 and NONROAD being replaced by new EPA/OTAQ MOVES model –Preliminary MOVES vs. MOBILE6 comparisons just becoming available

CMAS Motor Vehicle Emissions Simulator (MOVES) MOVES estimating times more PM 2.5 emissions from on- road mobile sources than MOBILE6 for three test cities (Source: Beardsley and Dolce, 2009)

CMAS Kansas City Vehicle Measurement Study KC motor vehicle measurements used in MOVES Also found high emission levels of Semi-Volatile Organic Compounds (SVOC) from LDGV –SVOC compounds not typically collected in vehicle exhaust VOC measurement studies  e.g., alkanes with 12 carbons or more, PAH compounds –SVOC emissions from LDGV 1.5 times the TC emissions  SVOC can condense to form an SOAA that would increase amount of TC from LDGVs  Unclear where condensed LDGV SVOC emissions would be in the CMB source apportionment (gasoline and/or UC)

CMAS Secondary Organic Aerosol (SOA) SOA an area of current research and development Significant progress over last 5 years –MEGAN biogenic emissions model –CMAQ SOAmods (2005), CAMx V4.5 (2008) and CMAQ V4.7 (2008)  Added SOAB from isoprene and sesquiterpene and other processes not treated in previous versions Several researchers are attributing more SOAA to aromatic VOC precursors (e.g., Toluene) than in current models –e.g., UofWI, NOAA, Kleindienst, etc.

CMAS VISTAS Source Apportionment Conclusions Comparison of CMB and CAMx/PSAT TC source apportionment provides insight into both methods and identifies areas for further research to improve our OCM modeling capability Current emission inventories underestimate particulate Carbon emissions from gasoline and diesel combustion –New MOVES on-road and non-road mobile source emissions factor model will make up much of the shortfall –KC vehicle study SVOC emissions may also help with gasoline OCM and/or SOAA shortfall –CMB gasoline contribution may also be overstated  Where are the stationary source TC contributions in the CMB analysis? SOA due to biogenic emissions is an area of current research –Implementation of SOA basis set treatment in CAMx will allow more flexibility in treating SOA from SVOC emissions and biogenic VOCs

CMAS Acknowledgements Acknowledge Dr. Eric Fujita’s colleagues at Desert Research Institute who performed sampling and CMB/PMF modeling –David Campbell, Johann Engelbrecht and Barbara Zielinska Acknowledge Woods Hole Oceanographic who made 14 C measurements that were documented by Roger Tanner of TVA This study was sponsored by VISTAS and acknowledge John Hornback and Ron Methier of SESARM for their support