1. Improving the Representation of Atmospheric Chemistry in WRF William R. Stockwell Department of Chemistry Howard University

2. Comparison of space-based measurements with CMAQ air quality model simulations shows that CMAQ overestimates NO 2 concentration near sources and it greatly under-predicts the NO 2 concentration outside of source regions. Comparison of NOAA P-3 ICARTT measurements with CMAQ air quality model simulations show: CMAQ has relatively low bias at altitudes less than 2 km for NO x and HNO 3, but at higher altitudes the CMAQ estimates are too low. PAN is an exception: CMAQ over-predicts at all altitudes with both CB4 and SAPRC chemical mechanisms. The absence of lightning NO x emissions is one obvious source of error at higher altitudes but sensitivity tests indicate that this is not the problem. CMAQ and WRF do not predict the observed range of ozone concentrations in general. CMAQ under-predicts NO x in the rural eastern U.S. atmosphere near the surface, as well as the NO x /NO y ratio during the day. Past chemical mechanism development and evaluation may have contributed to deficiencies in gas-phase chemistry. Atmospheric Chemistry Model Development

3. Summertime El Paso, TX CMAQ Obs-TCEQ WRF-CHEM R. Fitzgerald, et al., in preparation (2007) NOAA Center for Atmospheric Science - Howard University

4. Tropospheric NO 2 column density (molecules 10 15 cm -2 ) as observed from space (SCIAMACHY) and as estimated by the CMAQ air quality model for the summer of 2004. Air quality model overestimates NO 2 in source regions and it decreases much too rapidly away from sources. Source NOAA/ARL - EPA

5. Vertical Profiles of NOy: ICARTT Obs, CMAQ-SAPRC, CMAQ-CB5 O3O3 HNO 3 NO NO x /NO y PANNO 2 6000 (m) 0 (m) 6000 (m) 0 (m) 4000 (m) 0 (m) 4000 (m) 0 (m) 1000550002008040 2000216004001.00.0(ppt) (ppb)(ppt)

6. Regional Atmospheric Chemistry Mechanism, version 2 (RACM2) Ancestry RADM2 Regional Acid Deposition Mechanism, version 2 (Stockwell et al., 1990): Developed to predict Regional Atmospheric Chemistry and acid rain formation. RACM1 Regional Atmospheric Chemistry Mechanism, version 1 (Stockwell et al., 1997):  The aromatic chemistry scheme was improved using available laboratory data.  Included reaction schemes for biogenic compounds such as isoprene, limonene and  -pinene.

7. RACM2 RACM2 is being developed from RACM1. It contains a new schemes for: Acetone Aromatic compounds (based upon Calvert et al. (2002)) Isoprene (based upon Geiger et al. (2003) and improved by adding methyl vinyl ketone explicitly)  -Pinene d-Limonene About 110 Chemical Species in 300 Reactions

8. Key Research Activities and Objectives to Improve the Atmospheric Chemistry in WRF/Chem (1)Extend RACM2 to include organic aerosol formation. (2)Implement the Regional Atmospheric Chemical Mechanism (RACM2) and associated new aerosol chemistry in WRF. (3)Perform sensitivity tests to identify key parameters and reaction rates to prioritize chemical mechanism development efforts. (4)Given key sensitivities refine the chemical mechanism. (5)Assist in the comparison of WRF/Chem simulations with Satellite, Aircraft and Field Data.

9. Air Quality Modeling Projects that can be Leveraged for WRF/Chem Development Graduate Student Support: Air Quality Research NCAS Biogenic Organic Chemistry/Organic Aerosols/Climate NSF/NCAR WRF/Chem Meteorological and Air Quality Simulations NSF/NCAR Other Research Support: Development of RACM2 for CMAQ EPA/NOAA/ARL Collaboration in Air Quality Forecasting NOAA/NCEP

10. Conclusion Improving the Chem in WRF/Chem Air Quality Model Problems: Models fail to predict observed ranges of ozone mixing ratios. Comparison of space-based measurements with air quality model simulations shows that models overestimate NO 2 mixing ratios near sources and greatly under-predict them in rural regions. Past chemical mechanism development and evaluation for highly polluted conditions may have contributed to these and other model deficiencies. Proposed Research: Implement the gas-phase Regional Atmospheric Chemical Mechanism (RACM2) and extended aerosol chemistry based on RACM2 in WRF/Chem. Implement RACM2 and aerosol chemistry in WRF/Chem. Assist in the comparison of WRF/Chem simulations with satellite, aircraft and field data. Perform sensitivity tests to prioritize further mechanism development efforts.