Feature An ozone prediction map shows predicted ozone concentration. ArcGIS, site-by-site analyses were completed and the individual monitors ranked based on the number of parameters monitored at each site, measured concentrations, and the population and area served. Population and area served were represented by Thiessen polygons. Ranking gave insight into the importance of each monitoring site. Site-by-site analyses don’t evaluate the entire network, and each monitoring site is scored independently from the others. To understand the overall network and determine the deficiencies, further analyses were performed to examine the phenomena that influence high pollutant concentrations. The ArcGIS Geostatistical Analyst extension provides interpolation methods for producing surfaces based on the data samples. Kriging was used to produce the two raster surfaces— a map of predicted ozone values and a map of standard errors associated with ozone predicted values. Prediction standard error, distance to roads, population, NOx emissions, and VOC emissions grids were input to the weighted overlay analysis. The rasters were reclassified to a common scale of 1 to 10 (with 1 being the least suitable and 10 being the most suitable location for placing new monitors). Each raster was assigned percentage weights. The weighted overlay allows the user to look at the areas with the lowest suitability and where the uncertainty of the network is the greatest and place new monitors if needed. The model was built with ModelBuilder to ensure that the whole process could easily be repeated. Conclusion GIS and the tools developed by BAQ increased productivity and led to greater efficiency and accuracy. It became easy to query and analyze millions of records and display only relevant information. Since GIS has become an integral part of the BAQ’s daily operations, it is possible to make informed decisions and provide better services for the public. About the Author Elzbieta Covington is a GIS manager at the Bureau of Air Quality at the South Carolina Department of Health and Environmental Control. She came to the department in 2006 after working for 12 years at Earth Sciences and Resources Institute at the University of South Carolina. the years 2006–2008. The 300-meter and 500-meter back trajectories showed transport just south of the Atlanta area, eastward into the central Savannah River area of South Carolina. Exceedances of the 8-hour ozone standard occurred across the Atlanta area on May 2 and May 3, 2007. Ozone precursors from the Atlanta area moved into the central Savannah River area on May 3, 2007, and this, combined with meteorologic conditions, resulted in an ozone exceedance at the Jackson site. Ambient Air Monitoring Network Assessment BAQ is mandated by EPA to perform air monitoring network assessment every five years. The assessment determines if the new monitoring sites are needed and whether some of the existing sites can be terminated. The current assessment is in progress and has to be submitted to EPA in 2010. There are many steps involved in performing network assessment. With the use of www.esri.com ArcUser Summer 2010 29