What Controls the Ratio of Primary Reduced and Oxidized Forms of Gas Phase Reactive Nitrogen in Young Wildfire Smoke?

The Western wildfire Experiments for Cloud Chemistry, Absorbing Aerosol, and Nitrogen (WE-CAN) field campaign in July and August 2018 involved a comprehensive suite of gas phase and aerosol measurements on board the NSF/NCAR C-130 aircraft. During the WE-CAN intensive the NSF/NCAR C-130 sampled a diverse array of wildfire smoke plumes across the U.S. west. We report on fast-response in situ gas phase ammonia (NH₃) measurements in wildfire smoke, made with an Aerodyne QC-TILDAS (quantum cascade tunable infrared laser direct absorption spectrometer), and in situ measurements of NO and NO₂ from the NCAR 2-channel chemiluminescence instrument. The WE-CAN campaign, including the test flights that occurred in September 2017, represents the first deployment of active continuous passivation for rapid-response measurements of NH₃ from a research aircraft. Injecting a strong perfluorinated base (e.g., 1H,1H perfluorooctylamine) into the sample stream at the inlet tip prevents the adsorption of both water and basic species to instrument sampling surfaces. Using carbon monoxide from the NCAR Aerodyne QC-TILDAS CO instrument to identify smoke plumes, we investigate the ratio of primary reduced (NH₃) and oxidized (NO_x) fractions of reactive nitrogen in young wildfire smoke plumes. We relate different fire characteristics and environmental conditions such as modified combustion efficiency, fuel type, and relative humidity to the variability in this ratio and explore its influence on photochemistry during plume aging.