Inorganic Gas-Aerosol Partitioning in and around Concentrated Animal Feeding Operations

Ammonia (NH3) emissions from concentrated animal feeding operations (CAFOs) are an increasingly important source of reactive nitrogen in the US, but despite their ramifications to air quality and ecosystem health, few studies have aimed to quantify its near-source evolution. To this end, the Transport and Transformation of Ammonia (TRANS2AM) field campaign was conducted in the northeastern Colorado Front Range and characterized atmospheric composition downwind of CAFOs on 15 research flights under varying meteorological conditions. Airborne measurements of NH3, methane (CH4), nitric acid (HNO3), and water-soluble aerosol species collected onboard the University of Wyoming King Air (UWKA) research aircraft present a unique opportunity to (1) evaluate the current understanding of gas-aerosol partitioning through thermodynamic models and (2) investigate the sensitivity of particulate matter (PM) formation to CAFO emissions. Preliminary results from both the ISORROPIA-II and E-AIM IV aerosol thermodynamics models show that the modeled PM formation is highly sensitive to the presence of non-volatile cations (NVCs; e.g., Na+, K+, Mg2+, Ca2+), which are commonly found in dust particles. Hence, it is plausible that the particles sampled by the UWKA are an external mixture of dust and accumulation-mode particles from other sources, which influences NH3 partitioning. Finally, we investigate (1) the role of organic acids to the partitioning of inorganic species and (2) the overall enhancements of aerosol species within the plume relative to background.