A recently completed study by Walker et al. (2012) examined the feasibility of quantifying bulk soluble organic nitrogen (ON) concentrations in standard weekly National Atmospheric Deposition Program (NADP) National Trends Network (NTN) and daily Atmospheric Integrated Research Monitoring Network (AIRMoN) precipitation samples by comparison to a daily sample immediately refrigerated upon collection. Compared to the daily refrigerated sample, total loss of ON in weekly NTN samples in the field and during laboratory storage was approximately 40%.  Loss of ON was also observed in AIRMoN samples, though differences relative to the daily refrigerated sample (10.8%) were less than weekly NTN samples.  Storage experiments indicated that refrigeration at 4^oC at the NADP Central Analytical Laboratory (CAL) was sufficient to stabilize ON concentrations.  Walker et al. (2012) concluded that weekly sampling for ON may be feasible if precipitation is refrigerated immediately upon collection. The authors also recommended that nitrite (NO₂^-) be included as a component of the inorganic nitrogen from which the bulk ON concentration is calculated (i.e., ON = Total N – NH₄⁺ – NO₃^- – NO₂^-).

This study extends the work of Walker et al. (2012) by comparing refrigerated (weekly and daily) and unrefrigerated (weekly) samples collected using the a glass sampling train (i.e., glass collection funnel and amber glass sample collection bottle). The stability of ON in daily refrigerated versus weekly refrigerated samples is compared to assess the feasibility of weekly sampling of ON where daily sampling is logistically impractical or cost prohibitive.  Weekly refrigerated and unrefrigerated samples are compared to further assess, relative to Walker et al. (2012), potential losses of ON in weekly unrefrigerated field samples. Results comparing total soluble ON concentration, NH₄⁺, NO₃^-, and NO₂^- in weekly refrigerated, daily refrigerated, and weekly unrefrigerated samples are compared for the period January, 2013 to June, 2015 at a suburban forest site in the southeast U.S.   Relationships between the stability of nitrogen species, sample temperature, and precipitation chemical characteristics are also presented. 

Walker, J.T., Dombek, T., Green, L., Gartman, N., Lehmann, C. 2012.  Stability of organic nitrogen in NADP wet deposition samples. Atmospheric Environment, 60, 573 – 582.