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Intercomparison of Clean Air Status and Trends Network (CASTNET) NO3 - and HNO3 Measurements with Data from Other Monitoring Programs
Citation:
Lavery, T., C. Rogers, R. E. BAUMGARDNER, AND K. Mishoe. Intercomparison of Clean Air Status and Trends Network (CASTNET) NO3 - and HNO3 Measurements with Data from Other Monitoring Programs. JOURNAL OF AIR AND WASTE MANAGEMENT. Air & Waste Management Association, Pittsburgh, PA, 59:214-226, (2008).
Impact/Purpose:
Manuscript will be published in journal
Description:
The EPA Clean Air Status and Trends Network (CASTNET) utilizes an open face filter pack system to measure concentrations of atmospheric sulfur and nitrogen species. The purpose of this study was to estimate the uncertainty in seasonal and annual concentrations of HNO3, NO3 - , and NH4 +. Data from CASTNET, other monitoring networks, and inter-comparison studies were used to investigate the hypothesis that under certain conditions a fraction of the ammonium nitrate (NH4NO3) collected on the Teflon® filter dissociates into HNO3 and ammonia resulting in an overestimate of HNO3 concentrations and an underestimate of particulate NO3 -. Measurements of nitrogen species from the Maryland Aerosol Research and Characterization (MARCH) monitoring site at Ford Meade, MD were compared with nitrogen concentrations at three nearby CASTNET sites. Results indicate that CASTNET measured higher particulate NO3- and lower gaseous HNO3 concentrations although total nitrogen (HNO3+NO3-+NH4+) measurements were comparable. Comparisons of particulate nitrate measurements from 34 collocated CASTNET and Interagency Monitoring of Protected Visual Environments (IMPROVE) sites show that CASTNET nitrate measurements were typically higher than the corresponding IMPROVE values, although the site-to-site variability was considerable. While CASTNET uses an open face filter pack, both the MARCH and IMPROVE samplers have a size selective particle inlet.