Agricultural Emissions of Ammonia in California’s Central Valley

Ammonia (NH₃) is an unregulated air pollutant in the US. It contributes to fine particle formation and nitrogen deposition. Anthropogenic sources, particularly agriculture, combustion, and industrial activities, dominate emissions of NH₃. However, observations of the atmospheric sources, sinks, and phase partitioning of NH₃ are limited compared to other major anthropogenic pollutants. In contrast to declining emissions of nitrogen oxides (NO_x) from combustion sources, the emissions of NH₃ from combustion and agricultural activities have grown, and the deposition of reduced nitrogen has increased. Here, we use a suite of airborne trace gas measurements including NH₃, methane (CH₄), ethane (C₂H₆), carbon monoxide (CO), carbon dioxide (CO₂), nitrogen oxides (NO_x), and aircraft state parameters to identify and isolate emissions associated with agricultural operations in California’s Central Valley. New measurements highlighted in this work were collected aboard the NASA DC-8 aircraft during the Atmospheric Emissions and Reactions Observed from Megacities to Marine Areas (AEROMMA) field campaign conducted in summer 2023. We will use these measurements to quantify the ΔNH₃/ΔCH₄ enhancement ratios from agricultural operations in the Central Valley and compare them with prior reported values from ground-based and airborne studies in the Central Valley and in the Northeastern Colorado Front Range. Tracer-tracer relationships will be used to identify and isolate agricultural emissions from other sources such as oil and gas production activities, industry, and combustion.