Emissions of Nitrous Oxide and Methane in North America

Abstract

Methane (CH_4) and nitrous oxide (N_2O) are the second- and third-most important long-lived greenhouse gas species after carbon dioxide (CO_2) in terms of radiative forcing. This thesis describes the magnitude, spatial distribution, and seasonality of N_2O and CH_4 sources over North America using atmospheric data. We also investigate the environmental drivers and/or anthropogenic source sectors that can explain these emissions patterns. Overall, this thesis provides information on the magnitude, distribution, and likely drivers of greenhouse gas emissions to aid existing or future climate change mitigation policies in the US and Canada.

We estimate anthropogenic N_2O and CH_4 emissions that greatly exceed most existing inventory estimates. Our US budgets for N_2O and CH_4 are approximately 2.8 and 1.5 times higher, respectively, than inventory estimates from the US EPA. Much of the discrepancy in methane appears to stem from oil and natural gas industry and agricultural emissions.

In contrast, we estimate natural CH_4 sources that are smaller than most existing process-based biogeochemical models. These estimated fluxes have a spatial distribution centered around the Hudson Bay Lowlands. Most existing models estimate fluxes that are far more spatially distributed across the Canadian shield. These estimates provide negative information on the spatial distribution of fluxes relative to a spatially-constant model. We find that a simple model using only three environmental variables can describe flux patterns (as seen by the atmospheric observations) as well as any process-based estimate.