Development and Validation of a Commercial Dynamic Chamber System for Measuring Reactive Nitrogen Gas Fluxes

Nitrogen oxides (NO₂ + NO = NOx) and nitrous acid (HONO) are important trace pollutant gases in the atmosphere that catalyze and generate oxidants in the atmosphere, leading to the formation of ozone and other secondary pollutants. Production of HONO at atmospheric interfaces of many surfaces have been widely reported in recent years but the relative importance of experimentally identified sources and formation mechanisms remain poorly constrained. Furthermore, a large discrepancy exists between field and laboratory estimates of HONO fluxes from soils by orders of magnitude. Therefore, there is a clear need for a method which can be deployed in the field for obtaining HONO flux estimates and enable characterization of specific surface mechanisms. Here, we present a dynamic chamber system for HONO flux measurements developed for the first time by modification of commercially available chambers. We will present the rationale of the chamber along with the results of validation studies performed which minimize transformations of the reactive nitrogen species NO, NO₂ and HONO in the chambers. Chamber response times for each of these reactive gases and previously validated greenhouse gases (CH₄ and CO₂) will be compared to theoretically predicted values. Proof-of-concept lab and field measurements measuring reactive gas fluxes from agricultural soil surfaces will be presented, alongside co-located measurements of greenhouse gas fluxes with the new Picarro G2509 analyzer, which is also capable of measuring NH₃ and N₂O. The linkages between processes driving reactive and greenhouse gas fluxes will be explored in the context of our current understanding.