Investigating Gas-Particle Partitioning of Reduced Nitrogen in Western Wildfire Smoke

The partitioning of gas-phase ammonia into aerosol within wildfire smoke increases the lifetime of reduced nitrogen in the troposphere and impacts earth's radiation budget. Here, we report on in situ gas phase and aerosol measurements of reduced nitrogen species made on board the NSF/NCAR C-130 aircraft during the Western wildfire Experiment for Cloud Chemistry, Absorbing Aerosol, and Nitrogen (WE-CAN) field campaign in July and August 2018. We focus on measurements of smoke plumes that were sampled over the course of several hours of aging in order to investigate the gas-particle partitioning of ammonia within young western U.S. smoke plumes. We find significant variability in the fraction of ammonia converted to ammonium within 2-4 hours of aging. We explore this partitioning as a function of environmental parameters, initial fraction of reduced vs oxidized nitrogen, and the rate of photochemical oxidation within the plume, among other variables. We also employ an inorganic aerosol partitioning model (ISORROPIA) to examine whether inorganic partitioning may explain the total gas-particle conversion of ammonia in young smoke plumes or if other processes involving organic molecules should be considered.