Partitioning of Urban CO2ff Emissions By Source Sector: Results from the Influx Project

Tuesday, 16 December 2014: 4:20 PM
Jocelyn C Turnbull1,2, Anna Karion2,3, Colm Sweeney2,3, Timothy Newberger2,3, Scott Lehman4, Kenneth J Davis5, Thomas Lauvaux6, Natasha L Miles5, Scott Richardson5, Paul B Shepson7, Maria Obiminda L Cambaliza8, Kevin R Gurney9, Risa Patarasuk9 and James R Whetstone10, (1)GNS Science, National Isotope Centre, Lower Hutt, New Zealand, (2)University of Colorado at Boulder, CIRES, Boulder, CO, United States, (3)NOAA Boulder, ESRL, Boulder, CO, United States, (4)University of Colorado at Boulder, INSTAAR, Boulder, United States, (5)Penn State Univ, University Park, PA, United States, (6)Pennsylvania State University Main Campus, University Park, PA, United States, (7)Purdue Univ, West Lafayette, IN, United States, (8)Purdue University, West Lafayette, IN, United States, (9)Arizona State University, Tempe, AZ, United States, (10)National Institute of Standards and Technology Gaithersburg, Gaithersburg, MD, United States
Urban areas contribute ~75% of fossil fuel CO2 (CO2ff) emissions, and city governments are often leading the way in emission reduction efforts. As emissions are regulated and assigned a price, there is an increasing need to independently evaluate the reported bottom-up emissions and to attribute them to specific source sectors (e.g. electricity production, industry, vehicles). We demonstrate how multispecies atmospheric observations can be used to achieve this.

The Indianapolis Flux Experiment (INFLUX) aims to develop and evaluate methods for detection and attribution of urban GHG fluxes. The INFLUX observation network includes twelve towers measuring in situ CO2 and CO and flask measurements of another 50 species. 14CO2 measurements have shown that in winter, the total CO2 enhancement over Indianapolis approximates the CO2ff added. This somewhat surprising result allows us to use the wintertime in situ total CO2 and CO measurements to determine the observed CO:CO2ff ratio (RCO) at high resolution. First, we demonstrate that the USEPA CO inventory for Indianapolis overestimates CO emissions by a factor of about 2.5. Then we use the Hestia bottom-up CO2ff data product and revised characteristic RCO values for each CO2ff source sector to predict the diurnal cycle in RCO for Indianapolis. The tower observations and bottom-up RCO estimates are consistent during the daytime, but the observed RCO is significantly higher than the bottom-up estimate during the night. We show how the bottom-up and top-down methods can be used together to determine the cause of this discrepancy and improve CO2ff estimates from both methods.