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

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 NH _x. 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 NH _x 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 ppb_v. This work presents the first laboratory verified method for δ¹⁵N-NH₃ analysis and will be useful in future air quality studies.