Characterization of Reduced Nitrogen at IMPROVE and CSN Monitoring Sites in the Southeastern United States

Christopher Rogers1, John Walker2, Rich Scheffe3, Kevin Mishoe4, Doris Chen5, Katherine Barry6, Melissa Puchalski7, Bret Schichtel8 and Joann Rice9

The Interagency Monitoring of Protected Visual Environments (IMPROVE) and Chemical Speciation (CSN) networks have provided two decades of routine particulate matter (PM) speciation data that support regional haze and PM NAAQS programs. As shown by the NADP wet deposition record over the same period, the chemical composition of the ambient atmosphere has changed markedly from one dominated by nitrate, sulfate, and carbonaceous aerosols, and their associated precursor gases to an atmospheric mixture that includes a significant amount of reduced inorganic nitrogen – particulate ammonium (NH4+) and its precursor gas, ammonia (NH3). The magnitude of this change is reflected by a nationwide shift in the atmospheric composition from one dominated by inorganic oxidized compounds, to one where reduced inorganic nitrogen species (NHx = NH3 + NH4+) now have similar or greater contributions to the total nitrogen budget.

To address this change, it becomes necessary to characterize reduced nitrogen emission sources and atmospheric composition. Previous studies conducted primarily in the western United States have examined the possibility of using acid-impregnated filters in the IMPROVE system to measure NHx. Results were considered successful leading to a current study using acid-impregnated filters in both the IMPROVE and CSN systems to conduct similar measurements in the southeastern United States.

The study is occurring from late May through late November 2017 at Duke Forest, NC (near Research Triangle Park) and Gainesville, FL. Both sites are running CSN, IMPROVE, and URG annular denuder systems as the reference method to measure NHx. In addition, both sites include NH4+ and NH3 measurements from the CASTNET filter pack and NADP/AMoN, respectively. The Duke Forest site also has a Monitor for Aerosols and Gases in Ambient Air (MARGA) collecting hourly measurements of NH3 and NH4+. Here, results from the Duke Forest and Gainesville sites are compared to determine the feasibility of adding an acid-impregnated filter to capture NHx at a subset of the IMPROVE and CSN long-term measurement stations.


1Amec Foster Wheeler,
2USEPA, Office of Research and Development,
3USEPA, Office of Air Quality Planning and Standards,
4Amec Foster Wheeler,
5USEPA, Office of Research and Development,
6Amec Foster Wheeler,
7USEPA, Clean Air Markets Division,
8NPS, Cooperative Institute for Research in the Atmosphere, Colorado State University,
9USEPA, Office of Air Quality Planning and Standards,