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

Nitrogen stable isotope analysis (δN) of ammonia (NH) has shown potential to be a useful tool for characterizing emission sources and sink processes. However, to properly evaluate NH emission sources and sink processes under ambient conditions, it is necessary to collect and characterize the chemical speciation between NH and particulate ammonium (p-NH), together referred to as NH . Current NH collection methods have not been verified for their ability to accurately characterize δN-NH and/or provide necessary chemical speciation (i.e., δN-NH and δN-NH). Here, we report on the suitability of an established collection device that can provide NH 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 δN-NH under a variety of laboratory-controlled conditions and field collections. The collection method was tested under varying NH 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 δN-NH analysis is found to have excellent accuracy and precision of ±1.6‰ (2σ), with an operative capacity of ∼400 μg of collected NH for concentrations ≤207 ppb. This work presents the first laboratory verified method for δN-NH analysis and will be useful in future air quality studies.