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Robert Paine and Carl Berkowitz
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Daniel J. McNaughton, Carl M. Berkowitz, and Robert C. Williams

Abstract

Predicted concentrations from the Regional Air Pollutant Transport (RAPT) model are compared with the corresponding observed values of sulfate, and the results used to define strengths and weaknesses in the model formulation.

RAPT was developed to provide long-term (i.e., monthly) average values of pollutants. It has hourly time steps, and incorporates a number of simplifying assumptions on mixing heights, horizontal diffusion and emission averaging. Daily predicted values were analyzed for diagnostic use only, rather than for verification of prediction ability.

The analysis indicates that the model performed reasonably well with regard to short-term temporal predictions of spatially averaged concentrations. Less confidence can be placed in site-specific predictions. Spatial patterns in the analysis highlight the sensitivity of the model's short-term simulations to several features including input data, boundary conditions and the assumption of horizontal dispersion being wholly defined by trajectory variations.

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John W. Nielsen-Gammon, Christina L. Powell, M. J. Mahoney, Wayne M. Angevine, Christoph Senff, Allen White, Carl Berkowitz, Christopher Doran, and Kevin Knupp

Abstract

An airborne microwave temperature profiler (MTP) was deployed during the Texas 2000 Air Quality Study (TexAQS-2000) to make measurements of boundary layer thermal structure. An objective technique was developed and tested for estimating the mixed layer (ML) height from the MTP vertical temperature profiles. The technique identifies the ML height as a threshold increase of potential temperature from its minimum value within the boundary layer. To calibrate the technique and evaluate the usefulness of this approach, coincident estimates from radiosondes, radar wind profilers, an aerosol backscatter lidar, and in situ aircraft measurements were compared with each other and with the MTP. Relative biases among all instruments were generally less than 50 m, and the agreement between MTP ML height estimates and other estimates was at least as good as the agreement among the other estimates. The ML height estimates from the MTP and other instruments are utilized to determine the spatial and temporal evolution of ML height in the Houston, Texas, area on 1 September 2000. An elevated temperature inversion was present, so ML growth was inhibited until early afternoon. In the afternoon, large spatial variations in ML height developed across the Houston area. The highest ML heights, well over 2 km, were observed to the north of Houston, while downwind of Galveston Bay and within the late afternoon sea breeze ML heights were much lower. The spatial variations that were found away from the immediate influence of coastal circulations were unexpected, and multiple independent ML height estimates were essential for documenting this feature.

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Larry K. Berg, Carl M. Berkowitz, John A. Ogren, Chris A. Hostetler, Richard A. Ferrare, Manvendra K. Dubey, Elisabeth Andrews, Richard L. Coulter, Johnathan W. Hair, John M. Hubbe, Yin-Nan Lee, Claudio Mazzoleni, Jason Olfert, and Stephen R. Springston

The primary goal of the Cumulus Humilis Aerosol Processing Study (CHAPS) was to characterize and contrast freshly emitted aerosols below, within, and above fields of cumuli, and to study changes to the cloud microphysical structure within these same cloud fields in the vicinity of Oklahoma City during June 2007. CHAPS is one of few studies that have had an aerosol mass spectrometer (AMS) sampling downstream of a counterflow virtual impactor (CVI) inlet on an aircraft, allowing the examination of the chemical composition of activated aerosols within the cumuli. The results from CHAPS provide insights into changes in the aerosol chemical and optical properties as aerosols move through shallow cumuli downwind of a moderately sized city. Three instrument platforms were employed during CHAPS, including the U.S. Department of Energy Gulfstream-1 aircraft, which was equipped for in situ sampling of aerosol optical and chemical properties; the NASA Langley King Air B200, which carried the downward-looking NASA Langley High Spectral Resolution Lidar (HSRL) to measure profiles of aerosol backscatter, extinction, and depolarization between the King Air and the surface; and a surface site equipped for continuous in situ measurements of aerosol optical properties, profiles of aerosol backscatter, and meteorological conditions, including total sky cover and thermodynamic profiles of the atmosphere. In spite of record precipitation over central Oklahoma, a total of 8 research flights were made by the G-l and 18 by the B200, including special satellite verification flights timed to coincide with NASA satellite A-Train overpasses.

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