TY - JOUR
T1 - Stability of organic nitrogen in NADP wet deposition samples
AU - Walker, John T.
AU - Dombek, Tracy L.
AU - Green, Lee A.
AU - Gartman, Nina
AU - Lehmann, Christopher M.B.
N1 - Funding Information:
Mention of trade names does not constitute endorsement or recommendation of a commercial product by U.S. EPA. This research was partially funded by the U.S. Environmental Protection Agency , National Risk Management Research Laboratory, Research Triangle Park, NC . The authors gratefully acknowledge the assistance of Michael Snider, field site operator at Bondville, IL, for collecting and processing the field samples in this study.
PY - 2012/12
Y1 - 2012/12
N2 - Organic compounds represent an important yet largely uncharacterized component of atmospheric nitrogen deposition. Rapid progress in understanding the sources and spatiotemporal patterns of organic nitrogen (ON) deposition will require the use of existing large-scale monitoring infrastructure, such as the National Atmospheric Deposition Program's National Trends Network (NADP/NTN). The purpose of this study is to investigate the analytical and sampling requirements for adding ON measurements to the NTN, with specific interest in examining ON stability during sampling and storage. The analytical technique for total nitrogen (TN) used by the NADP's Central Analytical Laboratory (CAL) and associated quality assurance data are described. We then compare TN, inorganic nitrogen (IN = NH4+ + NO3-), and ON (ON = TN - IN) concentrations in a field study between standard weekly NADP/NTN samples (unrefrigerated during sampling and storage), daily event samples collected using the Atmospheric Integrated Research Monitoring Network protocol (AIRMoN, unrefrigerated during sampling but refrigerated during storage), and daily event samples that were preserved via refrigeration in the field upon collection (AIRMoN Ref, refrigerated during sampling and storage). Using AIRMoN Ref as the reference for comparison, total loss of ON in weekly NTN samples in the field and during laboratory storage is approximately 40%. This bias is likely dominated by losses of ON in the collection bucket. However, additional loss may occur during laboratory storage at room temperature prior to analysis. Loss of ON was also observed in AIRMoN samples, though differences relative to AIRMoN Ref (10.8%) were less than weekly NTN samples. Biases in ON are more consistently negative at higher ambient temperatures. Storage experiments indicated that refrigeration at 4 °C at the CAL was sufficient to stabilize ON concentrations. We conclude that weekly sampling for ON is feasible if precipitation is refrigerated or frozen immediately upon collection. Samples should be kept refrigerated or frozen prior to analysis. Preliminary results indicate that NO2-, an additional inorganic species not currently measured by the CAL, makes a small contribution to TN (<1%), but if neglected may cause significant negative bias in ON determined as TN - IN. We recommend that CAL include NO2- quantification as a component of IN for bulk ON determination.
AB - Organic compounds represent an important yet largely uncharacterized component of atmospheric nitrogen deposition. Rapid progress in understanding the sources and spatiotemporal patterns of organic nitrogen (ON) deposition will require the use of existing large-scale monitoring infrastructure, such as the National Atmospheric Deposition Program's National Trends Network (NADP/NTN). The purpose of this study is to investigate the analytical and sampling requirements for adding ON measurements to the NTN, with specific interest in examining ON stability during sampling and storage. The analytical technique for total nitrogen (TN) used by the NADP's Central Analytical Laboratory (CAL) and associated quality assurance data are described. We then compare TN, inorganic nitrogen (IN = NH4+ + NO3-), and ON (ON = TN - IN) concentrations in a field study between standard weekly NADP/NTN samples (unrefrigerated during sampling and storage), daily event samples collected using the Atmospheric Integrated Research Monitoring Network protocol (AIRMoN, unrefrigerated during sampling but refrigerated during storage), and daily event samples that were preserved via refrigeration in the field upon collection (AIRMoN Ref, refrigerated during sampling and storage). Using AIRMoN Ref as the reference for comparison, total loss of ON in weekly NTN samples in the field and during laboratory storage is approximately 40%. This bias is likely dominated by losses of ON in the collection bucket. However, additional loss may occur during laboratory storage at room temperature prior to analysis. Loss of ON was also observed in AIRMoN samples, though differences relative to AIRMoN Ref (10.8%) were less than weekly NTN samples. Biases in ON are more consistently negative at higher ambient temperatures. Storage experiments indicated that refrigeration at 4 °C at the CAL was sufficient to stabilize ON concentrations. We conclude that weekly sampling for ON is feasible if precipitation is refrigerated or frozen immediately upon collection. Samples should be kept refrigerated or frozen prior to analysis. Preliminary results indicate that NO2-, an additional inorganic species not currently measured by the CAL, makes a small contribution to TN (<1%), but if neglected may cause significant negative bias in ON determined as TN - IN. We recommend that CAL include NO2- quantification as a component of IN for bulk ON determination.
KW - Critical loads
KW - NADP
KW - Nitrogen deposition
KW - Organic nitrogen
KW - Wet deposition
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U2 - 10.1016/j.atmosenv.2012.06.059
DO - 10.1016/j.atmosenv.2012.06.059
M3 - Article
AN - SCOPUS:84865857800
SN - 1352-2310
VL - 60
SP - 573
EP - 582
JO - Atmospheric Environment
JF - Atmospheric Environment
ER -