Novel Tracer Method To Measure Isotopic Labeled Gas-Phase Nitrous Acid (HO¹⁵NO) in Biogeochemical Studies

Abstract

Gaseous nitrous acid (HONO), the protonated form of nitrite, contributes up to ∼60% to the primary formation of hydroxyl radical (OH), which is a key oxidant in the degradation of most air pollutants. Field measurements and modeling studies indicate a large unknown source of HONO during daytime. Here, we developed a new tracer method based on gas-phase stripping-derivatization coupled to liquid chromatography-mass spectrometry (LC-MS) to measure the 15N relative exceedance, ψ(15N), of HONO in the gas-phase. Gaseous HONO is quantitatively collected and transferred to an azo dye, purified by solid phase extraction (SPE), and analyzed using high performance liquid chromatography coupled to mass spectrometry (HPLC-MS). In the optimal working range of ψ(15N)=0.2-0.5, the relative standard deviation of ψ(15N) is <4%. The optimum pH and solvents for extraction by SPE and potential interferences are discussed. The method was applied to measure HO15NO emissions from soil in a dynamic chamber with and without spiking 15) labeled urea. The identification of HO15NO from soil with 15N urea addition confirmed biogenic emissions of HONO from soil. The method enables a new approach of studying the formation pathways of HONO and its role for atmospheric chemistry (e.g., ozone formation) and environmental tracer studies on the formation and conversion of gaseous HONO or aqueous NO2- as part of the biogeochemical nitrogen cycle, e.g., in the investigation of fertilization effects on soil HONO emissions and microbiological conversion of NO2- in the hydrosphere.

Emission of nitrous acid from soil and biological soil crusts represents a dominant source of HONO in the remote atmosphere in Cyprus

“…Here, we compare our results to studies which applied the same method (with the same or very similar conditions). The emission rates are consistent with these studies where HONO-N or NO-N emissions from soil between 1-3000 ng m -2 s -1 were found (Su et al, 2011;Oswald et al, 2013;Mamtimin et al, 2016;Wu et al, 2014;Weber et al, 2015). Mamtimin et al (2016) observed NO-N fluxes at 25°C of 57.5 ng m -2 s -1 , 18.9 ng m -2 s -1 and 4.1 ng m -2 s -1 for soil of grape and cotton fields and desert soil from an oasis in China, respectively.…”

“…The dynamic chamber method for analyzing NO and HONO emissions from soil samples was already introduced before (Oswald et al, 2013;Weber et al, 2015;Wu et al, 2014 and water vapor were quantified. HONO was analyzed with a commercial long path absorption photometer (LOPAP, QUMA GmbH; Wuppertal, Germany), with a detection limit of ~4 ppt and 10% uncertainty (based on the uncertainties of liquid and gas flow, concentration of calibration standard and regression of calibration).…”

Emission of nitrous acid from soil and biological soil crusts represents an important source of HONO in the remote atmosphere in Cyprus

“…Here, we compared our results to studies that applied the same method (with the same or very similar conditions). The emission rates were consistent with the studies in which HONO-N or NO-N emissions from soil between 1 and 3000 ng m −2 s −1 were found (Su et al, 2011;Oswald et al, 2013;Mamtimin et al, 2016;Wu et al, 2014;Weber et al, 2015). Mamtimin et al (2016) observed NO-N fluxes of 57.5, 18.9 and 4.1 ng m −2 s −1 at 25 • C for soil of grape and cotton fields and desert soil from an oasis in China, respectively.…”

“…The dynamic chamber method for analyzing NO and HONO emissions from soil samples was already introduced before (Oswald et al, 2013;Weber et al, 2015;Wu et al, 2014) and in general showed good agreement with flux measurements in the field (van Dijk et al, 2002;Rummel et al, 2002). Under the prevailing dry and hot conditions in Cyprus, macropores and cracks are likely to be present in the soil layer.…”

Biological soil crusts accelerate the nitrogen cycle through large NO and HONO emissions in drylands

“…Further investigations comprising multiple nitrogen compounds and isotopes should unravel the interplay of different chemical and biological species and processes in the cycling of nitrogen by biocrusts (33)(34)(35)(36).…”