EPA's Clean Air Status and Trends Network (CASTNET) is a long-term atmospheric monitoring program with approximately 90 sites located throughout the United States with one site located in Canada. Since its inception in 1986 as the National Dry Deposition Network, CASTNET has featured quality assured measurements of ambient temperature predominately at a 9-meter probe height. To examine statistical trends in the data record, hourly temperature data were retrieved from 50 CASTNET sites and split into six regions across the United States: Northeast, Southeast, Midwest, Southwest, Rocky Mountain, and Pacific. The data ranges from 1990 to 2021 for sites in the eastern United States, and 1995 to 2021 for western sites. Linear regression of the annual temperatures over time was used to illustrate the rate of change in temperature for each region and season. Prior to the analysis, missing data were replaced using linear interpolation, and outliers were identified and removed.

The results illustrate an increasing trend for spring, summer, and fall for all regions, a decreasing trend for winter in the Pacific, Rocky Mountain and Midwest regions, and an increasing trend for winter in the Southwest, Southeast and Northeast regions. Improved analysis and additional years of data are required to enhance future temperature trend observations. It is recommended that seasonal trend analysis is done on data sets spanning more than thirty years for small geographical regions and a geo-spatial statistical approach be considered for interpolation of missing data before calculating annual averages.

¹ WSP USA Environment & Infrastructure, Gainesville, FL

² WSP USA Environment & Infrastructure, Jacksonville, FL

* Corresponding Author: jayde.alderman@wsp.com