Collection of Ammonia for High Time-Resolved Nitrogen Isotopic Characterization Utilizing an Acid-Coated Honeycomb Denuder

Nitrogen stable isotope analysis (δ15N) of ammonia (NH3) has shown potential to be a useful tool for characterizing emission sources and sink processes. However, to properly evaluate NH3 emission sources and sink processes under ambient conditions, it is necessary to collect and characterize the chemical speciation between NH3 and particulate ammonium (p-NH4+), together referred to as NHx. Current NH3 collection methods have not been verified for their ability to accurately characterize δ15N-NH3 and/or provide necessary chemical speciation (i.e., δ15N-NH3 and δ15N-NH4+). Here, we report on the suitability of an established collection device that can provide NHx speciation, an acid-coated (2% citric acid (w/v) + 1% glycerol (w/v) in 80:20 methanol to water solution) honeycomb denuder (HCD) with a downstream filter pack housed in the ChemComb Speciation Cartridge (CCSC), for characterizing δ15N-NH3 under a variety of laboratory-controlled conditions and field collections. The collection method was tested under varying NH3 concentration, relative humidity, temperature, and collection time at a flow rate of 10 L per minute (LPM). The acid-coated HCD collection device and subsequent chemical processing for δ15N-NH3 analysis is found to have excellent accuracy and precision of ±1.6‰ (2σ), with an operative capacity of ∼400 μg of collected NH3 for concentrations ≤207 ppbv. This work presents the first laboratory verified method for δ15N-NH3 analysis and will be useful in future air quality studies.