1. Office of Research and Development National Exposure Research Laboratory, Atmospheric Modeling and Analysis Division Office of Research and Development National Exposure Research Laboratory Golam Sarwar, Wyat Appel, Annamrie Carlton, Rohit Mathur, Keneth Schere, Mohammed Majeed October 11, 2010 Impact of an updated toluene mechanism on air quality in the western US

2. Office of Research and Development National Exposure Research Laboratory, Atmospheric Modeling and Analysis Division Office of Research and Development National Exposure Research Laboratory Background Chemical mechanisms are a critical component of air quality models Toluene is an imporant chemical compound that can affect O 3 and SOA; however its chemistry is poorly understood Different chemical mechanisms use different approximations for toluene chemistry Models using different chemical mechanisms produce different results – Faraji et al. (2008) noted CB-IV & SAPRC99 lead up to 40 ppbv O 3 difference in Houston A large part of the difference was attributed to differences in aromatic chemistry – Whitten et al. (2010) updated the toluene chemistry in CB05 (Whitten et al., 2010. A new condensed toluene mechanism for Carbon Bond: CB05-TU, AE)

3. Office of Research and Development National Exposure Research Laboratory, Atmospheric Modeling and Analysis Division Office of Research and Development National Exposure Research Laboratory Background Chemical mechanisms are evaluated using chamber experimental results – updated toluene chemistry performed better than base chemistry Earlier, we evaluated impact of the updated toluene chemistry on air quality in the eastern US (Sarwar et al., 2010) – Monthly mean 8-hr O 3 increased by up to 2.0 ppbv Here, we examine impact of the updated toluene chemistry on O 3 and PM in the western US

4. Office of Research and Development National Exposure Research Laboratory, Atmospheric Modeling and Analysis Division Office of Research and Development National Exposure Research Laboratory TOL CRESTO2 NTR OH CRO OPEN OH HO2 (benzaldehyde) 36%56% 8% NO 10%90% OH NTR NO2 HO2 C2O3 PAN NO2 Ref: Yarwood et al., 2005 Existing toluene chemistry in CB05 mechanism CB05-Base (simplified)

5. Office of Research and Development National Exposure Research Laboratory, Atmospheric Modeling and Analysis Division Office of Research and Development National Exposure Research Laboratory TOL CRES TO2 NTR OH CRO OPEN OH HO2 (benzaldehyde) 18% 65% 10% NO 14%86% OH CRON NO2 HO2 OPO3 OPAN NO2 OH 7% CRNO 2 NTR CRN2 O3 NO OH NO2 CRPX OH Ref: Whitten et al., 2010 Updated toluene chemistry in CB05 mechanism CB05-TU (simplified)

6. Office of Research and Development National Exposure Research Laboratory, Atmospheric Modeling and Analysis Division Office of Research and Development National Exposure Research Laboratory Modeling details CMAQ model CMAQ model version 4.7 was used Horizontal grid resolution = 12-km Number of horizontal grids = 213 X 192 Number of vertical layers = 14 Surface layer thickness = 36 meter Simulation period: July 1 – 31, 2002 Two different model simulations were performed – with CB05-Base – with CB05-TU Used generalized Rosenbrock solver for gas-phase chemistry – Model with CB05-TU required 6% additional computational time

7. Office of Research and Development National Exposure Research Laboratory, Atmospheric Modeling and Analysis Division Office of Research and Development National Exposure Research Laboratory Modeling details Meteorology and emissions Meteorological fields – PSU/NCAR MM5 system Anthropogenic emissions – 2002 National Emissions Inventory (NEI) Biogenic emissions – Biogenic Emissions Inventory System (BEIS) Model-ready emissions – Sparse Matrix Operator Kernel Emission (SMOKE)

8. Office of Research and Development National Exposure Research Laboratory, Atmospheric Modeling and Analysis Division Office of Research and Development National Exposure Research Laboratory CMAQ: impact on daily maximum 8-hr O 3 Changes in mean 8-hr O 3 (CB05-TU - CB05-Base) Mean TOL/VOC (CB05-Base) Monthly mean 8-hr O 3 (CB05-Base) O 3 increases where toluene/VOC ratio is high ppbv

9. Office of Research and Development National Exposure Research Laboratory, Atmospheric Modeling and Analysis Division Office of Research and Development National Exposure Research Laboratory CMAQ: variation of daily maximum 8-hr O 3 (CB05-TU – CB05-Base) While CB05-TU increases daily maximum 8-hr O 3 by up to 5-6 ppbv, impact on many other days are low to moderate Los AngelesPortlandSeattle

10. Office of Research and Development National Exposure Research Laboratory, Atmospheric Modeling and Analysis Division Office of Research and Development National Exposure Research Laboratory CMAQ: NO z with CB05-Base and increases in NO z with CB05-TU Monthly mean NO z with CB05-Base Changes in mean NO z (CB05-TU - CB05-Base) CB05-TU increases NO z compared to CB05-Base

11. Office of Research and Development National Exposure Research Laboratory, Atmospheric Modeling and Analysis Division Office of Research and Development National Exposure Research Laboratory CMAQ: ozone production efficiency (OPE) CB05-Base at Los Angeles CB05-TU at Los Angeles CB05-TU increases O 3 but not OPE

12. Office of Research and Development National Exposure Research Laboratory, Atmospheric Modeling and Analysis Division Office of Research and Development National Exposure Research Laboratory Comparison with observed data Daily maximum 8-hr O 3 at Seattle MB with CB05-TU decreases slightly at higher observed O 3 and increased slightly at lower observed O 3

13. Office of Research and Development National Exposure Research Laboratory, Atmospheric Modeling and Analysis Division Office of Research and Development National Exposure Research Laboratory Comparison with observed data Daily maximum 8-hr O 3 at Los Angeles MB decreases slightly with CB05-TU at all observed O 3

14. Office of Research and Development National Exposure Research Laboratory, Atmospheric Modeling and Analysis Division Office of Research and Development National Exposure Research Laboratory Impact on SOA from toluene Monthly mean SOA with CB05-Base CB05-TU / CB05-Base Predicted SOA increased slightly with CB05-TU (maximum 7%) However, impact on PM 2.5 was also small

15. Office of Research and Development National Exposure Research Laboratory, Atmospheric Modeling and Analysis Division Office of Research and Development National Exposure Research Laboratory Summary Updated toluene chemistry enhances monthly mean 8-hr O 3 by up to 2.8 ppbv Updated toluene chemistry produces more NO z than CB05-Base Updated toluene chemistry increase O 3 but not OPE Updated toluene chemistry slightly decreases MB at higher observed O 3 Updated toluene chemistry slightly increases SOA; impact on PM 2.5 is smaller Results are consistent with those reported by Sarwar et al. (2010) for eastern US – CB05-TU increased monthly mean 8-hr O 3 by up to 2.0 ppbv in eastern US