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Abstract Ammonia (NH₃) from animal feeding operations (AFOs) is an important source of reactive nitrogen in the US, but despite its ramifications for air quality and ecosystem health, its near‐source evolution remains understudied. To this end, Phase I of the Transport and Transformation of Ammonia (TRANS²Am) field campaign was conducted in the northeastern Colorado Front Range in summer 2021 and characterized atmospheric composition downwind of AFOs during 10 research flights. Airborne measurements of NH₃, nitric acid (HNO₃), and a suite of water‐soluble aerosol species collected onboard the University of Wyoming King Air research aircraft present an opportunity to investigate the sensitivity of particulate matter (PM) formation to AFO emissions. We couple the observations with thermodynamic modeling to predict the seasonality of ammonium nitrate (NH₄NO₃) formation. We find that during TRANS²Am northeastern Colorado is consistently in the NH₃‐rich and HNO₃‐limited NH₄NO₃formation regime. Further investigation using the Extended Aerosol Inorganics Model reveals that summertime temperatures (mean: 23°C) of northeastern Colorado, especially near the surface, inhibit NH₄NO₃formation despite high NH₃concentrations (max: ≤114 ppbv). Finally, we model spring/autumn and winter conditions to explore the seasonality of NH₄NO₃formation and find that cooler temperatures could support substantially more NH₄NO₃formation. Whereas NH₄NO₃only exceeds 1 μg m⁻³∼10% of the time in summer, modeled NH₄NO₃would exceed 1 μg m⁻³61% (88%) of the time in spring/autumn (winter), with a 10°C (20°C) temperature decrease relative to the campaign. 

Abstract Phase One of the Transportation and Transformation of Ammonia (TRANS²Am) field campaign took place in northeastern Colorado during the summer of 2021. One of the goals of TRANS²Am was to measure ammonia (NH₃) emissions from cattle feedlots and dairies. Most of these animal husbandry facilities are co‐located within oil and gas development, an important source of methane (CH₄) and ethane (C₂H₆) in the region. Phase One of TRANS²Am included 12 near‐source research flights. We present estimates of NH₃emissions ratios with respect to CH₄(NH₃EmR), with and without correction of CH₄from oil and gas, for 29 feedlots and dairies in the region. The data shows larger emissions ratios than previously reported in the literature with a large range of values (i.e., 0.1–2.6 ppbv ppbv⁻¹). Facilities housing cattle and dairy had a mean (std) of 1.20 (0.63) and 0.29 (0.08) ppbv ppbv⁻¹, respectively. We also found that only 15% of the total ammonia (NH_x) is in the particle phase (i.e., ) near major sources during the warm summertime months. We examined the evolution of NH₃in one plume that was sampled at different distances and altitudes up to 25 km downwind and estimated the NH₃lifetime against deposition and partitioning to the particle phase to be 87–120 min. Finally, we calculated estimates of NH₃emission rates from four optimally sampled facilities. These ranged from 4 to 29 g NH₃ · h⁻¹ · hd⁻¹.