Individual methane emissions from animal feeding operations in northeastern Colorado Front Range.

Abstract:

In complicated regions containing anthropogenic and biogenic emissions, source interference creates difficulties measuring individual plumes. Distinguishing the sources of methane in these regions is essential to reduce uncertainties associated with the quantification of individual emissions. In this study, we conduct a detail analysis for agriculture plumes interfering with oil and natural gas operations. During November of 2019, the University of Wyoming King Air research aircraft (UWKA) completed three test flights in the northeast Colorado Front Range measuring methane (CH₄), ethane (C₂H₆) and ammonia (NH₃). This location has a high number of concentrated animal feeding operations (CAFOs) that house large numbers of beef and dairy cattle including CAFOs nearing 100 thousand cattle heads. However, this area also has many oil and natural gas operations which makes it difficult to separate CH₄ sources. During test flights, the UWKA flight paths were executed around CAFOs to allow upwind and downwind spirals, and stacked transects downwind. The UWKA’s small aircraft size was able to conduct these flight patterns with tight turns and lower flying speeds, allowing for 1 Hz data to be collected with an average 90 m/s ground speed during the transects providing high resolution. On November 13^th, 2019, UWKA flew transects downwind of one large CAFO with high cattle head capacity. The results show distinct plumes of NH₃ and CH₄, indicating large emissions from the CAFO, with areas of high C₂H₆ from oil and natural gas extraction emissions. Both C₂H₆ to CH₄ and NH₃ to CH₄ enhancement ratios are demonstrated to distinguish the sources of the elevated CH₄ values. Finally, the CH₄ emission rates from the individual CAFO is calculated by removing other interfering emissions. Current results show overall CH₄ values within the transect to be ~3700 g/s with C₂H₆ values of 609 g/s and NH₃ values of 505 g/s. However with removing oil and natural gas emissions, through the C₂H₆ to CH₄ enhancement ratio, the agriculture CH₄ decreases to ~510 g/s. The sensitivity of these results to different assumptions of C₂H₆ to CH₄ ratios is also discussed. These rates will provide for a better understanding of CH₄ budgets and decrease the uncertainties around interfering sources in complicated regions.