Near‐Source Ammonia (NH<sub>3</sub>) Fluxes and Evolution Observed From Airborne Measurements in Plumes Up To 25 km Downwind From Large Beef Cattle Facilities | CU Experts

AbstractThe Transport and Transformation of Ammonia (TRANS2Am) campaign took place in northeastern Colorado in the summers of 2021 and 2022. One of the goals of TRANS2Am was to study the evolution of ammonia (NH3) in plumes from large animal feeding operations. This work investigates the nearfield deposition of NH3 in four plumes from large animal husbandry facilities observed during TRANS2Am using a mass balance approach with methane (CH4) as a conservative tracer in the timescales of plume transport. Since the plumes in TRANS2Am were not sampled in a pseudo‐Lagrangian manner, an empirical model is developed to correct for variations in summertime NH3 emissions as a function of time of day. The mass balance approach results show that the average summertime NH3 decay time to 80% and 60% against deposition in plumes from large animal sources is 43 (+11/−7) and 85 (+19/−14) min, respectively. Additionally, we present estimates of net fluxes every 5 km downwind of the plume. Under the hot, dry summertime midday conditions sampled during TRANS2Am, we found that within 10–15 km of the large emission sources studied, NH3 undergoes net deposition. Beyond this distance, the complex environmental exchange of NH3 between the atmosphere and the surface suggests that fresh NH3 emissions from smaller nearby sources could switch the direction of the net flux to emission.

Juncosa Calahorrano JF; Sullivan AP; Pollack IB; Roscioli JR; Caulton DR; McCabe ME; Steinmann KM; Li E; Pierce JR; Naimie LE

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