Modification and validation of a commercial dynamic chamber for reactive nitrogen and greenhouse gas flux measurements

Abstract

Reactive nitrogen gases (NO, NO2, HONO, NH3 and others; Nr) play important roles in atmospheric processes, and their cascading impacts throughout the Earth system have adverse effects on both the environment and human health. The fluxes of these gases at the surface-atmosphere interface have been studied in isolation or smaller subsets, but simultaneous fluxes of all Nr alongside standard greenhouse gases (GHGs) have not been reported. Here, a dual-dynamic chamber system was developed for Nr by modifying a commercially available system for GHG fluxes for use with destructive analyzers. It includes a reference chamber to account for chemical reactions and surface interactions. The resulting platform makes the measurement of Nr and by extension, other reactive gases, more widely accessible to the scientific community because custom chambers do not need to be fabricated. System modifications to passivate surfaces reduced an initial 36 % loss of NO2 to below analyzer detection limits (∼ 10 %) for relevant atmospheric conditions. The modified 72 L chamber response times (τ) did not change for GHGs or NO (τ = 37–39 min versus a theoretical 36 min) at a flow rate of 2 L min−1. The modifications improved the transfer of NO2, HONO, and NH3 by up to 2 min, but substantial surface interactions for NH3 remain. A surface interaction term was characterized for these gases to obtain accurate field fluxes via a mass balance framework. Proof-of-concept measurements of Nr fluxes from agricultural soil samples under controlled lab conditions as a function of soil water content were able to quantify emissions of NO, NO2, HONO, NH3, and N2O simultaneously. We observed soil fluxes without amendment and when subject to Nr fertilization. Unfertilized soils showed variability in NO2 and HONO emissions when soil structure was minimally disturbed, consistent with in-situ field measurements from other researchers. These oppose maximum potential fluxes in prior lab soil manipulations, particularly for HONO relative to NO. Last, Nr field fluxes were quantified with the dual-chamber system on an in-use agricultural soil, including baseline conditions and a urea-based fertilizer perturbation to stimulate microbial and chemical transformation and transfer Nr to the atmosphere. Good agreement with other field flux techniques was found. The mass balance terms within the dual-chamber approach are fully inspected from the pilot deployment in the field, along with an error analysis, to aid in the uptake of this approach by the community.