Science Inventory

Improving characterization of reduced nitrogen at IMPROVE and CSN monitoring sites


Rogers, C., K. Mishoe, M. Stewart, K. Barry, J. Rice, X. Chen, JohnT Walker, M. Puchalski, R. Baumgardner, AND B. Schichtel. Improving characterization of reduced nitrogen at IMPROVE and CSN monitoring sites. U.S. Environmental Protection Agency, Washington, DC, 2021.


Total reduced nitrogen (NHx) measurements are not routinely performed in the US and currently no regulatory requirements exist to measure NHx. However, scientific and policy interest in the increasing trend in NHx concentrations in many regions of the US has evolved since NHx can lead to atmospheric fine particulate matter (PM2.5) formation and visibility impairment and, once atmospherically deposited, can cause eutrophication, loss of species biodiversity and algal blooms. This study, set in the southeastern US, was designed to measure total and speciated NHx and to assess measurement methods for implementation in long-term monitoring networks, specifically the Interagency Monitoring of Protected Visual Environments (IMPROVE) and Chemical Speciation (CSN) networks. Incorporating an NHx measurement into the CSN and IMPROVE networks would leverage existing infrastructure, reduce costs and provide national monitoring coverage.


The goal of this study was to determine whether acid-coated filters could be deployed at existing sites using existing network equipment to measure NHx concentrations in hot, humid environments. Acid-coated filters were deployed in both CSN and IMPROVE systems in North Carolina and Florida during the summer of 2017. For CSN and IMPROVE, a filter module containing a phosphorous acid (H3PO3) impregnated cellulose filter was adding to the sampler. A URG annular denuder filter pack system (ADFPS) was used as a reference method to measure NHx as well it’s components NH3 and NH4+. This report summarizes comparisons between the measurement systems for NHx and additional measurements to characterize aspects of sampler performance.

Record Details:

Product Published Date: 01/18/2021
Record Last Revised: 02/05/2021
OMB Category: Other
Record ID: 350728