Assessment of fossil fuel carbon dioxide and other anthropogenic trace gas emissions from airborne measurements over Sacramento, California in spring 2009

Abstract

Abstract. Direct quantification of fossil fuel CO 2 (CO 2 ff) in atmospheric samples can be used to examine several carbon cycle and air quality questions. We collected in situ CO 2 , CO, and CH 4 measurements and flask samples in the boundary layer and free troposphere over Sacramento, California, USA, during two aircraft flights over and downwind of this urban area during spring of 2009. The flask samples were analyzed for 14 CO 2 and CO 2 to determine the recently added CO 2 ff mole fraction. A suite of greenhouse and other trace gases, including hydrocarbons and halocarbons, were measured in the same samples. Strong correlations were observed between CO 2 ff and numerous trace gases associated with urban emissions. From these correlations we estimate emission ratios between CO 2 ff and these species, and compare these with bottom-up inventory-derived estimates. Recent county level inventory estimates for carbon monoxide (CO) and benzene from the California Air Resources Board CEPAM database are in good agreement with our measured emission ratios, whereas older emissions inventories appear to overestimate emissions of these gases by a factor of two. For most other trace species, there are Correspondence to: J. C. Turnbull (jocelyn.turnbull@noaa.gov) substantial differences (200-500%) between our measured emission ratios and those derived from available emission inventories. For the first flight, we combine in situ CO measurements with the measured CO:CO 2 ff emission ratio of 14 ± 2 ppbCO/ppmCO 2 to derive an estimate of CO 2 ff mole fraction throughout this flight, and also estimate the biospheric CO 2 mixing ratio (CO 2 bio) from the difference of total and fossil CO 2 . The resulting CO 2 bio varies dramatically from up to 8 ± 2 ppm in the urban plume to −6 ± 1 ppm in the surrounding boundary layer air. Finally, we use the in situ estimates of CO 2 ff mole fraction to infer total fossil fuel CO 2 emissions from the Sacramento region, using a mass balance approach. The resulting emissions are uncertain to within a factor of two due to uncertainties in wind speed and boundary layer height. Nevertheless, this first attempt to estimate urban-scale CO 2 ff from atmospheric radiocarbon measurements shows that CO 2 ff can be used to verify and improve emission inventories for many poorly known anthropogenic species, separate biospheric CO 2 , and indicates the potential to constrain CO 2 ff emissions if transport uncertainties are reduced.

Surface observations for monitoring urban fossil fuel CO2 emissions: Minimum site location requirements for the Los Angeles megacity

“…Recent examples have started to attempt to specifically attribute emissions [Turnbull et al, 2011;Newman et al, 2012] and perform trend detection over time [McKain et al, 2012]. These studies suggest that attribution and trend detection with atmospheric observations are possible.…”

Application of Gauss's theorem to quantify localized surface emissions from airborne measurements of wind and trace gases

“…The seminal experiment began with Keeling's acclaimed CO 2 curve (1960), and has continued through more contemporary techniques by Hirsch et al (2006) and Neef et al (2010) for CH 4 and N 2 O, respectively. At progressively smaller scales more details of the source strengths and apportionment can be made: from synoptic or continental scales which can help constrain national inventories (Bergamaschi et al, 2005) or specific biogeographic regions (Gallagher et al, 1994), to mesoscale investigations that estimate emissions from urban areas (Mays et al, 2009;Turnbull et al, 2011;Wecht et al, 2014) or specific oil-and gas-producing fields (Karion et al, 2013; and even down to individual point/area sources on the order of 10-100 m size (Denmead et al, 1998;Lavoie et al, 2015;Roscioli et al, 2015).…”

Carbon monoxide isotopic measurements in Indianapolis constrain urban source isotopic signatures and support mobile fossil fuel emissions as the dominant wintertime CO source

“…Turnbull et al, 2015;Parrish et al, 2006;Graven et al, 2009;LaFranchi et al, 2013;EPA NEI 2011). In addition to the atmospheric chemistry and health impacts, CO has been explored as a tracer for fossil fuel derived CO 2 (CO 2ff ) (Meijer et al, 1996;Levin and Karstens, 2007;Turnbull et al, 2006;Vogel et al, 2010;Turnbull et al, 2011;Turnbull et al, 2015). This method relies on an assumption that CO is produced entirely by combustion, which is not always true within urban regions (Turnbull et al, 2015).…”