Enhancements in Ammonia and Methane from Agricultural Sources in the Northeastern Colorado Front Range Using Observations from a Small Research Aircraft.

Quantifying ammonia (NH 3 ) to methane (CH 4 ) enhancement ratios from agricultural sources is important for understanding air pollution and nitrogen deposition. The northeastern Colorado Front Range is home to concentrated animal feeding operations (CAFOs) that produce large emissions of NH 3 and CH 4 . Isolating enhancements of NH 3 and CH 4 in this region due to agriculture is complicated because CAFOs are often located within regions of oil and natural gas (O&NG) extraction that are a major source of CH 4 and other alkanes. Here, we utilize a small research aircraft to collect in situ 1 Hz measurements of gas-phase NH 3 , CH 4 , and ethane (C 2 H 6 ) downwind of CAFOs during three flights conducted in November 2019. Enhancements in NH 3 and CH 4 are distinguishable up to 10 km downwind of CAFOs with the most concentrated portions of the plumes typically below 0.25 km AGL. We demonstrate that NH 3 and C 2 H 6 can be jointly used to separate near-source enhancements in CH 4 from agriculture and O&NG. Molar enhancement ratios of NH 3 to CH 4 are quantified for individual CAFOs in this region, and they range from 0.8 to 2.7 ppbv ppbv -1 . A multivariate regression model produces enhancement ratios and quantitative regional source contributions that are consistent with prior studies.