Detecting fossil fuel emissions patterns from subcontinental regions using North American in situ CO2 measurements

Y.P. Shiga, A.M. Michalak, S.M. Gourdji, K.L. Mueller and V. Yadav

Using atmospheric observations to estimate national level fossil fuel emissions would allow for independent verification of fossil fuel emissions estimates that currently rely on accurate self-reporting and a variety of assumptions (e.g. fuel type, combustion efficiency). The goal of independently estimating fossil fuel emissions from atmospheric CO2 observations relies on the ability to differentiate the fossil fuel signal from the natural CO2 signal and other background signals. To reach this goal we must first ask, when and where can we distinguish fossil fuel emissions patterns using atmospheric CO2 observations? In this study, we explore this very question using the 35 tower North American CO2 monitoring network. We find that natural CO2 fluxes and atmospheric transport patterns drastically hamper the detection of fossil fuel emissions patterns during spring, summer and fall and that winter offers the best conditions for detecting and thus estimating fossil fuel emissions using atmospheric CO2 data.

Figure: Results of the model selection analysis by region and season. Colors represent the number of months per season (0 to 3) for which the FF emissions from a region are detectable. Red stars represent continuous observation locations for 2008. The percent of region-months detected per season (Number detected / 33 total region-months × 100%) is also shown.


The ability to monitor fossil fuel carbon dioxide (FFCO2) emissions from subcontinental regions using atmospheric CO2 observations remains an important but unrealized goal. Here we explore a necessary but not sufficient component of this goal, namely, the basic question of the detectability of FFCO2 emissions from subcontinental regions. Detectability is evaluated by examining the degree to which FFCO2 emissions patterns from specific regions are needed to explain the variability observed in high-frequency atmospheric CO2 observations. Analyses using a CO2 monitoring network of 35 continuous measurement towers over North America show that FFCO2 emissions are difficult to detect during nonwinter months. We find that the compounding effects of the seasonality of atmospheric transport patterns and the biospheric CO2 flux signal dramatically hamper the detectability of FFCO2 emissions. Results from several synthetic data case studies highlight the need for advancements in data coverage and transport model accuracy if the goal of atmospheric measurement-based FFCO2 emissions detection and estimation is to be achieved beyond urban scales.

Shiga, Y.P. , A.M. Michalak, S.M. Gourdji, K.L. Mueller, V. Yadav (2014) "Detecting fossil fuel emissions patterns from subcontinental regions using North American in situ CO2 measurements", Geophysical Research Letters, 41, doi:10.1002/2014GL059684.