The processing actions described below are automated by a combination of MS Dos batch scripts and visual basic programming. The main program is called once each day using Windows Scheduler.

At 7 am each day, a modified version of the WebGet Internet File Retriever is used to download all valid hourly concentrations of ozone and PM2.5 from EPA’s AIRNOWTECH (www.airnowtech.org) website. The current retrieval is limited to monitoring stations located in Texas, Louisiana, Arkansas, and Oklahoma. The monitoring data are imported into MicroSoft Access and a series of queries and macros are used to merge the observational data with the site-specific latitude and longitude information. Basic quality assurance (range checks) are performed before the data are exported into a comma-delimited ASCII text file.

Golden Software's Surfer (www.goldensoftware.com) is used to interpolate the monitoring data to a regular grid. For each hour, all available data are used in the interpolation regardless of the data completeness for that day at a given monitoring station.  The Kriging interpolation scheme is invoked using default options (Variogram Model: Slope = 1, Anisotropy = 1,0; Kriging Type = Point; Drift Type = None. For more information, Kriging references are provided below.) The gridded data are contoured using a 15 ppb contour interval for ozone and a 5 ug/m3 interval for pm2.5. The locations of the monitoring stations with valid data for that hour are labeled using a "+" symbol.  Each hourly map is exported in Windows Media File (wmf) format to maintain the original color scheme.

The hourly contour maps are inserted into MicroSoft PowerPoint and provided to the user as ready to view movies (*.pps) or downloadable files (*.ppt). The PPS files are preset with a one second time delay between frames.

For more information, contact Gary McGaughey.

Kriging References (From Golden Software’s Surfer “Help Topics”)

For a detailed derivation and discussion of Kriging see Cressie (1991) or Journel and Huijbregts (1978). Journel (1989) is, in particular, a concise presentation of geostatistics (and Kriging). Isaaks and Srivastava (1989) offer a clear introduction to the topic, though it does not cover some of the more advanced details. For those who need to see computer code to really understand an algorithm, Deutsch and Journel (1992) includes a complete, well-written, and well-documented source code library of geostatistics computer programs (in FORTRAN). Finally, a well-researched account of the history and origins of Kriging can be found in Cressie (1990).

Abramowitz, M., and Stegun, I. (1972), Handbook of Mathematical Functions, Dover Publications, New York.

Cressie, N. A. C. (1990), "The Origins of Kriging," Mathematical Geology, v. 22, p. 239-252.

Cressie, N. A. C. (1991), Statistics for Spatial Data, John Wiley and Sons, Inc., New York, 900 pp.

Deutsch, C.V., and Journel, A. G. (1992), GSLIB - Geostatistical Software Library and User's Guide, Oxford University Press, New York, 338 pp.

Isaaks, E. H., and Srivastava, R. M. (1989), An Introduction to Applied Geostatistics, Oxford University Press, New York, 561 pp.

Journel, A.G., and Huijbregts, C. (1978), Mining Geostatistics, Academic Press, 600 pp.

Journel, A.G. (1989), Fundamentals of Geostatistics in Five Lessons, American Geophysical Union, Washington D.C.