Dataset includes reduced nitrogen (NHx) concentrations that were collected at Duke Forest, NC and Gainesville, FL using a CSN MetOne SuperSASS and IMPROVE PM sampler from May - October 2017. Using an acid impregnated filter in the CSN and IMPROVE samplers, NHx concentrations were compared to URG annular denuder measurements. Results are summarized in a report: Improving characterization of reduced nitrogen at IMPROVE and CSN monitoring sites (https://www.epa.gov/system/files/documents/2021-11/nhx_summary-report_final.pdf). Citation information for this dataset can be found in the EDG's Metadata Reference Information section and Data.gov's References section.