United States Environmental Protection Agency Office of Research and Development National Exposure Research Laboratory Research Abstract Government Performance Results Act (GPRA) Goal # 4 Annual Performance Measure # 274 Significant Research Findings: Estimates of the Distribution and Patterns of Atmospheric Nitrogen Stressors' Airborne Concentration and Deposition in the Eastern US Scientific To determine the impact(s) of legislatively driven pollutant control strategies, Problem and baseline conditions must be defined. This research documents the seasonal Policy Issues behavior and spatial patterns of both dry and wet nitrogen species in the eastern US just prior to the January, 1995 implementation of Phase I of the Clean Air Act Amendments of 1990. Research The goal was to define the seasonal and spatial patterns of nitrogen species" Approach concentration and deposition in the eastern US. Monitoring data from two national networks were used to perform this research. Dry data came from EPA's CASTNET (Clean Air Status and Trends Network) and wet data came from NADP (National Acid Deposition Program). Weekly dry and wet concentration, and dry and wet deposition of selected nitrogen species monitored at or near 34 rural sites in the east were adjusted for known biases and composed into seasonal values according to peer-reviewed protocols. To ensure representative results, five-year (1990-1994) averages were examined. Results and In the East, dry concentration, deposition velocity, precipitation, and dry, wet, and Impact total deposition of each of the monitored chemical constituents display regular seasonal cycles of behavior. With few exceptions, seasonal extremes tend to occur in the summer and winter. Much of the seasonal behavior may be explained by summertime enhancement of atmospheric chemistry and convective processes. Nitric acid (HN03) is the dominant contributor to dry deposition of measured oxidized nitrogen (NOx) and measured total nitrogen (N). Wet deposition is a major contributor to total deposition, generally peaking in the summer or spring. Total NOx, and N deposition peak in the summer, with summertime measured total deposition exceeding the winter value by a factor of ~2. Dry deposition of HN03, NOx, and N is the highest at the high elevation subset of sites. The proportion of dry to total deposition also appears to be highest at high elevation sites in the East, underscoring the importance of dry deposition as a stressor to high elevation ecosystems in the eastern US. This documentation of the seasonal behavior and spatial patterns of both dry and wet nitrogen species in the eastern US just prior to the implementation of Phase I of the Clean Air Act Amendments of 1990 (i.e., January 1, 1995) will help define the baseline against which future changes resulting from legislatively mandated control strategies can be detected, measured and demonstrated. ------- Research Collaboration and Research Products Examples of recent publications from this study include: Shadwick, D. S., Sickles, J. E.. II, 2004. Sample size for seasonal mean concentration deposition velocity, and deposition: a resampling study. Atmospheric Enviromnent 38, 477-489. Sickles, J. E., II, Shadwick, D. S., 2002a. Biases in the Clean Air Status and Trends Network filter pack results associated with sampling protocol. Atmospheric Enviromnent 29, 4687-4698. Sickles, J. E., II, Shadwick, D. S., 2002b. Precision of atmospheric dry deposition data from the Clean Air Status and Trends Network. Atmospheric Environment 36, 5671-5686. Future Research A study contrasting the behavior of nitrogen species in the first half of the 1990's (1990-1994) with that in the second half (1995-1999) is underway. Upon its completion, a second study will begin of the changes occurring after 2000 when several oxides of nitrogen (NOx) control measures commenced. Contacts for Additional Information Questions and inquiries can be directed to: Joseph E. Sickles, II, Ph.D. U.S. EPA, Office of Research and Development National Exposure Research Laboratory, MD-E243-05 Research Triangle Park, North Carolina 27711 Phone: 919/541-2446 E-mail: sickles.ioseph@epa.gov Funding for this project was through the U.S. EPA's Office of Research and Development, National Exposure Research Laboratory, and the work was conducted by the Environmental Sciences Division, Landscape Characterization Branch. Additional funding for this research was administered under EPA contract number 68-W01032. ------- |