Spurious nitrous oxide emissions from acidic nitrite solutions: a cautionary tale on the critical role of experimental apparatus

Nitrite (NO₂⁻) is known to undergo disproportionation into nitric oxide (NO) and nitrogen dioxide (NO₂) via an abiotic pathway in acidic aqueous solutions. However, whether a direct pathway for its conversion to nitrous oxide (N₂O) exists remains unclear. This study investigated this potential pathway under both ambient air and nitrogen-purged conditions. Initial experiments yielded substantial N2O production, appearing to validate a novel abiotic process in the nitrogen cycle. However, through a series of exclusion experiments involving physical barriers and comparative analysis of sealing materials, these emissions were revealed to be entirely spurious. Analysis of water extracts from these materials demonstrated dissolved organic carbon (DOC) concentrations ranging from 37.67 to 736.8 μg g−1. A significant positive correlation (R2 = 0.585, p = 0.047) between leachable DOC and headspace N2O accumulation indicates that organic leachates from the stoppers serve as the primary substrates for this artifact. Mechanistically, the reaction is initiated by the volatilization of nitrous acid (HONO) from the acidic solution, which subsequently partitions into the condensed water film on the stopper surface. Within this interface, HONO undergoes reduction coupled with the oxidation of leached organic electron donors—a process that was significantly suppressed under oxygen-depleted conditions. Crucially, this experimental error was effectively mitigated by using rigid polypropylene (PP) caps, premium-grade silicone stoppers, or by subjecting standard stoppers to alkali washing. These findings highlight the unintended reactivity of seemingly inert materials as a critical error source, underscoring the imperative for rigorous apparatus validation to prevent misinterpreting fundamental biogeochemical processes.