Abstract

This review paper explores recent efforts to estimate state and national-scale carbon dioxide (CO2) and methane (CH4) emissions from individual anthropogenic source sectors in the United States. Nearly all state and national climate change regulations in the US target specific source sectors, and detailed monitoring of individual sectors presents a greater challenge than monitoring total emissions. We particularly focus on opportunities to synthesize disparate types of information on emissions, including emissions inventory data and atmospheric greenhouse gas data. 5 We find that inventory estimates of sector-specific CO2 emissions are sufficiently accurate for policy evaluation at national scale but that uncertainties increase at state and local levels. CH4 emissions inventories are highly uncertain for all source sectors at all spatial scales, in part because of the complex, spatially-variable relationships between economic activity and CH4 emissions. In contrast to inventory estimates, top-down estimates use measurements of atmospheric concentrations to infer emissions at the surface; these efforts have had little success identifying CO2 emissions from anthropogenic sources 10 but have successfully identified sector-specific CH4 emissions in several opportunistic cases. We also describe a number of forward-looking opportunities that would aid efforts to estimate sector-specific emissions: fully combine existing top-down datasets, expand intensive aircraft measurement campaigns and measurements of secondary tracers, and improve the economic and demographic data (e.g., activity data) that drive emissions inventories. These steps would better synthesize inventory and top-down data to support sector-specific emissions reduction policies. 15