labs_title

Constraining sector-specific CO2 and CH4 emissions in the US

S.M. Miller and A.M. Michalak

We review recent efforts to estimate state- and national-scale carbon dioxide (CO2) and methane (CH4) emissions from individual anthropogenic source sectors in the United States. Examples include total CO_2 emissions from coal power plants or total methane emissions from the natural gas industry. State and federal greenhouse gas regulations almost always target reductions from specific source sectors, and reliable emission estimates are important to support these policies. In the paper, we evaluate the reliability of existing emissions estimates and make several recommendations for future improvements. Overall, we find that CO2 emissions estimates are often sufficiently accurate to support state and national policy evaluation but that CH4 estimates are highly uncertain for most important source sectors.


Figure: This figure displays different estimates for CO2 and CH4 emissions in the US, broken down by source sector. These estimates are from the Environmental Protection Agency and EDGAR (Emissions Database for Global Atmospheric Research). CO2 totals are consistent among different estimates, but CH4 totals vary widely, an indication of uncertainty in CH4 emissions. (Note that EDGAR includes CO2 from heating in its electricity estimate while EPA does not. As a result, the EDGAR CO2 estimate is higher than EPA's estimate.)

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 US. 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 emission inventory data and atmospheric greenhouse gas data.

We find that inventory estimates of sector-specific CO2 emissions are sufficiently accurate for policy evaluation at the national scale but that uncertainties increase at state and local levels. CH4 emission 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 mixing ratios to infer emissions at the surface; thus far, these efforts have had some success identifying urban CO2 emissions and 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 emission inventories. These steps would better synthesize inventory and top-down data to support sector-specific emission reduction policies.

Miller, S.M., A.M. Michalak(2017) "Constraining sector-specific CO2 and CH4 emissions in the US", Atmospheric Chemistry and Physics, 17 (6), 3963-3985, doi:10.5194/acp-17-3963-2017.