The Atmospheric Impact of Energy and Food Production

Abstract

Fossil fuel extraction and modern industrial agricultural practices both emit greenhouse gases and pollutants, including methane (CH4), nitrous oxide (N2O), ethane (C2H6), and black carbon (BC). Our understanding of emissions magnitudes, processes that control these emissions, and expected future emissions behavior from these sources and of these important atmospheric compounds have large uncertainty. Accurate, precise measurements made from aircraft can provide essential insights into emissions and their impact on climate and air quality. This thesis presents airborne observations using high-precision spectroscopy of atmospheric greenhouse gases and pollutants to quantify emissions. First, with airborne measurements we assess natural gas flaring efficiency of CH4, C2H6, and BC in the Bakken Shale region of North Dakota. We discover emissions from flares exhibit a heavy-tailed distribution and superemitter behavior with a small number of inefficient flares dominating the total source. This skewed distribution translates to total flaring emissions of CH4 and C2H6 that are 2.5 times higher than if standard flare efficiency is assumed. While we observe a skewed distribution for BC, emissions are lower than previous estimates and there is no significant correlation with CH4 emissions. Next, we describe the development and evaluation of an airborne system using an N2O, CO2, CO, and H2O laser spectrometer. Ambient pressure-related artifacts in the instrument are corrected for with a mass flow-controlled frequent calibration technique to achieve an 88% duty cycle with high precision and accuracy. The resultant flight system represents the current state-of-the-art airborne N2O system. Finally, with this new system and a series of flights, emissions from agricultural activity and fertilizer production are evaluated in the Lower Mississippi River Basin. The quantification of emission rates from two productive fertilizer plants finds good agreement with reported emissions of N2O and CO2, but a large underestimation in CH4, suggesting significant natural gas leakage. We calculate N2O emissions fluxes from cropland using the airborne mass balance technique, a first application of this method for N2O. The impact on emissions by associated factors—crop type, fertilizer application, soil moisture, and soil temperature—is investigated. We find the strongest predictors in a multiple linear regression are soil moisture and crop type. An average early-growing season N2O flux of 1.8 ± 1.4 g N2O-N ha^-1 hr^-1 is quantified for the region. The results demonstrate the ability to evaluate N2O emissions at regional scales from sources with large environmental heterogeneity using airborne observations. This thesis highlights the utility of aircraft measurements for investigating emissions of greenhouse gases and pollutants at varying spatial scales and from diverse sources associated with energy and food production supply chains.