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Diagnostic Ozone Sensitivity Tests the St. Louis 8-Hour Ozone and PM 2.5 Study

Diagnostic Ozone Sensitivity Tests the St. Louis 8-Hour Ozone and PM 2.5 Study. Ralph Morris, Ou Nogmoncol, Abby Hoats, Gerry Mansell and Chris Emery ENVIRON International Corporation St. Louis 8-Hour Ozone/PM 2.5 Workgroup Meeting March 20, 2006. Background.

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Diagnostic Ozone Sensitivity Tests the St. Louis 8-Hour Ozone and PM 2.5 Study

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  1. Diagnostic Ozone Sensitivity Tests the St. Louis 8-Hour Ozone and PM2.5 Study Ralph Morris, Ou Nogmoncol, Abby Hoats, Gerry Mansell and Chris Emery ENVIRON International Corporation St. Louis 8-Hour Ozone/PM2.5 Workgroup Meeting March 20, 2006

  2. Background • Phase I of the St. Louis 8-Hour Ozone and PM2.5 Study developed three 8-hour ozone episodes for the CAMx and CMAQ models • Working with the Four Modeling Hubs, the episodes were evaluated • Ozone performance characterized by a general underestimation bias • CAMx was performing better than CMAQ • Given time constraints, Modeling Hubs decided to focus on the CAMx model for 8-hour ozone

  3. Background • Ozone underestimation tendency • St. Louis urban core ozone hole overstated • Modeled ozone formation too slow so that peaks occur further downwind than observed • Magnitudes of the peaks comparable to observed • Potential causes of ozone performance • Insufficient sunlight intensity • Insufficient vertical mixing • Too little VOC in StL • Too much NOx in StL • Other???

  4. Sensitivity Tests • Analyze MM5 cloud estimates to see if excessive – attenuates photolysis rates • Perform sensitivity tests • Base 3 w/ Mech 3 (compare with Mech4) • Kz_min =1.0 m2/s • Kvpatch with Kz_min =2.0 m2/s • 1.5 x ISOP (biogenic) • 1.5 x non-ISOP VOC (anthropogenic) • 0.75 x NOx (anthropogenic)

  5. 8-hr Ozone June 21, 2002 CAMx Mech 4 Base 2

  6. 8-hr Ozone July 15, 2002 CAMx Mech 4 Base 2

  7. Example Cloud EvaluationFairly Good Agreement – No Over-statement MM5 Predicted Satellite

  8. June/July Episode Sensitivity • Mech 3: Norm Bias = -13% to -38% • Mech 4: Norm Bias = -9% to -32% • Mech 4 improves Bias by 2-5 percentage points • Likely due to renoxification reaction • Kzmin = 2.0 m2/s • Improves bias by ~2 percentage points

  9. June/July Episode Sensitivity • Mech 3 & Kzmin=2: Norm Bias –12% to –36% • 1.5 x Biogenic Isoprene Emissions • Improvement in June (south wind) episode with Norm Bias increasing 3-5 percentage points • Little effect for July episode • 0.75 x Anthropogenic NOx Emissions • Little effects (Norm Bias <+2% change) • Urban ozone increases offset by rural ozone reductions • 1.5 x Anthropogenic VOC Emissions • Minor (1 percentage point increase) improvements

  10. Base 3 Mech 3 Kz_min=2.0 1.5 x ISOP 0.75 x NOx June 21, 2002 Daily Maximum 8-Hour Ozone (ppb)

  11. Kz_min=2.0 Base 3 Mech 3 0.75 x NOx 1,5 x ISOP July 15, 2002 Daily Maximum 8-Hour Ozone (ppb)

  12. Emission Sensitivity Tests • 1.5xISOP emissions sensitivity buys about 5% points in bias for June 21, little effect on July 15 • June 21 has transport from south where high biogenic isoprene occurs • Supports rerunning biogenic emissions with MM5 temperatures adjusted to correct bias • 0.75xNOx & 1.5xnon-ISOP VOC less of an effect • Although overstated low-level NOx in urban core could still be part of the problem

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