Linking emissions of fossil fuel CO₂ and other anthropogenic trace gases using atmospheric ¹⁴CO₂

Abstract

[1] Atmospheric CO 2 gradients are usually dominated by the signal from net terrestrial biological fluxes, despite the fact that fossil fuel combustion fluxes are larger in the annual mean. Here, we use a six year long series of 14 CO 2 and CO 2 measurements obtained from vertical profiles at two northeast U.S. aircraft sampling sites to partition lower troposphere CO 2 enhancements (and depletions) into terrestrial biological and fossil fuel components (C bio and C ff ). Mean C ff is 1.5 ppm, and 2.4 ppm when we consider only planetary boundary layer samples. However, we find that the contribution of C bio to CO 2 enhancements is large throughout the year, and averages 60% in winter. Paired observations of C ff and the lower troposphere enhancements (D gas ) of 22 other anthropogenic gases (CH 4 , CO, halo-and hydrocarbons and others) measured in the same samples are used to determine apparent emission ratios for each gas. We then scale these ratios by the well known U.S. fossil fuel CO 2 emissions to provide observationally based estimates of national emissions for each gas and compare these to "bottom up" estimates from inventories. Correlations of D gas with C ff for almost all gases are statistically significant with median r 2 for winter, summer and the entire year of 0.59, 0.45, and 0.42, respectively. Many gases exhibit statistically significant winter:summer differences in ratios that indicate seasonality of emissions or chemical destruction. The variability of ratios in a given season is not readily attributable to meteorological or geographic variables and instead most likely reflects real, short-term spatiotemporal variability of emissions.

Global emissions of refrigerants HCFC-22 and HFC-134a: Unforeseen seasonal contributions

“…Refrigerant leakage studies suggest neither the gradual leaks (i.e., regular emissions) nor the immediate release (i.e., break of the air conditioning system) have significant seasonal dependences (12,13). In contrast, a few regional atmospheric studies suggest that emissions of HCFC-22 and HFC-134a may be seasonal due to weather-dependent patterns in refrigerator and air conditioner use (14)(15)(16)(17)(18)(19). This uncertainty in seasonality indicates incomplete knowledge of the underlying mechanisms that lead to atmospheric release.…”

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

“…This suggested that during the winter at Indianapolis, non-fossil fuel sources of CO do not contribute significantly. In contrast, during the summer, there is weaker correlation between CO and 14 C-derived CO 2ff , suggesting another summertime source of CO in Indianapolis (Turnbull et al, 2015) and in other locations (Turnbull et al, 2006;Miller et al, 2012). Stable isotopic measurements of urban CO can help quantify individual CO sources and sinks and provide an improved understanding of seasonal changes in the urban CO budget (e.g.…”

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

“…The third method of source quantification is to reference measurements of the unknown trace gas to a reference trace gas with a metered release (tracer) or otherwise-known emission rate and assume that the tracer and the scalar of interest have the same diffusion characteristics. Typically this tracer release technique is applied to small scales of tens to hundreds of meters (Czepiel et al, 1996;Lamb et al, 1995;Roscioli et al, 2015), but the principle has been attempted at the basin (Peischl et al, 2013) and continental (Miller et al, 2012) scales using a reference trace gas with a suitable known emission rate such as CO 2 or CO.…”