Improving the Representation of Atmospheric Chemistry in WRF

William R. StockwellDepartment of Chemistry

Howard University

Comparison of space-based measurements with CMAQ air quality model simulations shows that CMAQ overestimates NO2 concentration near sources and it greatly under-predicts the NO2 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 NOx and HNO3, 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 NOx 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 NOx in the rural eastern U.S. atmosphere near the surface, as well as the NOx/NOy ratio during the day.

Past chemical mechanism development and evaluation may have contributed to deficiencies in gas-phase chemistry.

Atmospheric Chemistry Model Development

Summertime El Paso, TX

CMAQObs-TCEQ

WRF-CHEM

R. Fitzgerald, et al., in preparation (2007)NOAA Center for Atmospheric Science - Howard University

Tropospheric NO2 column density (molecules 1015 cm-2) as observed from space (SCIAMACHY) and as estimated by the CMAQ air quality model for the summer of 2004.

Air quality model overestimatesNO2 in source regions and it decreases much too rapidly away from sources.

Source NOAA/ARL - EPA

Source NOAA/ARL - EPA

Vertical Profiles of NOy: ICARTT Obs, CMAQ-SAPRC, CMAQ-CB5 O3HNO3NO

NOx/NOyPANNO2

600

0 (

m)

0 (

m)

600

0 (

m)

0 (

m)

400

0 (

m)

0 (

m)

400

0 (

m)

0 (

m)

10005 5000200 8040

20002 1600400 1.00.0(ppt) (ppt)

(ppb)(ppt) (ppt)

Regional Atmospheric Chemistry Mechanism, version 2 (RACM2) Ancestry

RADM2Regional Acid Deposition Mechanism, version 2 (Stockwell et al., 1990): Developed to predict Regional Atmospheric Chemistry and acid rain formation.

RACM1Regional 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.

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

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.

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

ConclusionImproving 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 NO2 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.