Long-Term Variability and Source Signature of Gases Emitted from Oil and Natural Gas and Cattle Feedlot Operations in the Colorado Front Range

Multiple tropospheric gases are analyzed in eight years of observations using a ground-based solar absorption Fourier Transform InfraRed (FTIR) instrument in the Colorado Northern Front Range (CNFR). The first year of measurements in 2010 coincide with the tremendous increase of oil and natural (O&NG) extraction in the region. We show seasonal variations and trends of atmospheric gases related to these activities (C₂H₆, CH₄). In addition, results are presented for gases related to cattle feedlot operations (NH₃), urban emissions (CO, C₂H₂), and volatile organic compounds related to photo-chemistry and ozone production (H₂CO, HCOOH). A significant positive trend of about 5 %·yr^-1 has been reported for C₂H₆ from 2010 to mid 2014 (Franco et al., 2016). We will show that that trend has not been sustained and the revised linear trend is 0.27 ± 0.41 %·yr^-1 through 2017. This coincides with a decline in the production of oil in the region during 2015 to 2017. NH₃ shows the greatest annual rate of change (5.6 ± 1.1 %·yr^-1) during this period that may be due to an increase in the emissions related to cattle feedlot operations or to the decrease in NH₃ removal via its rate limiting reaction with H₂SO₄ from a reduction in coal power plant emissions. Simulations of the evolution of these gases are presented using the CAM-Chem model and are compared with FTIR observations Finally, we will show here a concise approach to identify local enhancements of gases related to nearby O&NG and concentrated animal feedlot operations. These enhancements are used to estimate emission ratios (ER) relative to CO, which lead to estimates emission factors (EF) of co-emitted species. We will present results for HCN emissions from a western US biomass burning event, and C₂H₆ from O&NG activities. We further complement the study by analyzing airborne observations during the Front Range Air Pollution and Photochemistry Experiment (FRAPPE) intensive period in 2014.