Determination of Total Dissolved Nitrogen (TDN) in Wet Deposition Samples Preserved During Collection and Post Collection

Tracy Dombek1, Christopher Lehmann1 and John Walker2

Concentrations of ammonium and nitrate, the dissolved components of nitrogen, are routinely determined in wet deposition samples analyzed by the National Atmospheric Deposition Program/Central Analytical Laboratory (NADP/CAL). To quantify the contribution of all nitrogen species, the U.S. EPA has provided funding to the NADP/CAL to analyze total dissolved nitrogen (TDN) in select NADP National Trends Network (NTN) and Atmospheric Integrated Research Monitoring Network (AIRMoN) samples. This data set will provide additional information on spatio-temporal patterns of nitrogen in deposition, and determine the feasibility of operating a national-scale network to measure TDN.

There is evidence in the literature that organic fractions of nitrogen are unstable and sample preservation must be considered when evaluating the total nitrogen concentration in wet deposition. A collocated sampler study was conducted by the CAL at its monitoring site located at Bondville, IL during summer 2009 (June 1 August 31). The purpose of this study was to compare total, organic, and inorganic nitrogen measurements for weekly NTN samples, daily AIRMoN samples, and daily samples from a third chilled collector. Preliminary data indicate that the AIRMoN and field-chilled samples have higher total nitrogen concentrations than NTN samples.

Two additional sample preservation techniques were evaluated on samples with adequate volume. Select NTN and AIRMoN samples from Bondville were acidified to pH < 2.0 using sulfuric acid and some samples were frozen post-collection. This poster will present a comparison of the nitrogen species concentrations in the NTN, AIRMoN, and field-chilled samples as well as a comparison of sample preservation methods (field-chilled, acidified, and frozen). Quality assurance data will also be presented to quantify method detection limits, analytical reproducibility, and analytical bias.

1 Central Analytical Laboratory, National Atmospheric Deposition Program, 2204 Griffith Dr.; Champaign, IL 61820; 217-265-6812; .
2 U.S. EPA, National Risk Management Research Laboratory, Air Pollution Prevention and Control Division, Research Triangle Park, NC; 919-541-2288; .