Data assimilation and air quality - Air Pollution Modeling and Its Application - page 263

profile. Multiple local minima of the measured RH indicated co-location of
various cloudy air-mass prevailed over the site. Therefore cloud mixing activities
were speculated to have contributed to the rather uniform profiles.
Unlike the previous two sites, Huntsville, LA is a non-elevated site. The
overshot of 250 m or larger in PBL height prediction was not uncommon during a
developing PBL (Fig. 3) . From measure RH profile, PBL height was inferred to be
at 1,500 m AGL at launch time. In terms of instantaneous surface O 3 concentration,
Cases b, and c performed slightly better than that by Case a. There is virtually no
difference in vertical O 3 concentration profiles between Cases b and c.
At Beltsville, MD, there was an over-estimated PBL height. It was overshot by
about 1,000 m. The inferred PBL height was 1,250 m ( Fig. 4) . The measured O 3
concentration showed well-mixed behavior below the PBL top as reflected rather
well by Cases b and c. Cases b and c illustrated the capping of the mixing activity
below the predicted PBL height by about 500 m as indicated by the inflexion
points of model-predicted O 3 concentration profiles.
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Acknowledgments The authors appreciate numerous valuable discussions with Drs. Rohit
Mathur, Jon Pleim, David Wong, Tanya Otte, George Pouliot, Brian Eder, Jeff Young, and Ken
Schere of the Atmospheric Modeling Division of the National Exposure Research Laboratory,
U.S. EPA. The U.S. EPA AIRNow program staff provided the observations necessary for
quantitative model evaluation. The authors are indebted to Mr. Jerry Gorline of Meteorological
Development Laboratory of NOAA for providing Fig. 1b.