Constraints on emissions of carbon monoxide, methane, and a suite of hydrocarbons in the Colorado Front Range using observations of <sup>14</sup>CO<sub>2</sub>
Atmospheric radiocarbon (<sup>14</sup>C) represents an important observational constraint on emissions of fossil-fuel derived carbon into the atmosphere due to the absence of <sup>14</sup>C in fossil fuel reservoirs. The high sensitivity and precision that accelerator mass sp...
| Main Authors: | , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2013-11-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/13/11101/2013/acp-13-11101-2013.pdf |
| Summary: | Atmospheric radiocarbon (<sup>14</sup>C) represents an important observational
constraint on emissions of fossil-fuel derived carbon into the atmosphere due
to the absence of <sup>14</sup>C in fossil fuel reservoirs. The high sensitivity
and precision that accelerator mass spectrometry (AMS) affords in atmospheric
<sup>14</sup>C analysis has greatly increased the potential for using such
measurements to evaluate bottom-up emissions inventories of fossil fuel
CO<sub>2</sub> (CO<sub>2</sub>ff), as well as those for other co-emitted species. Here we
use observations of <sup>14</sup>CO<sub>2</sub> and a series of primary hydrocarbons and
combustion tracers from discrete air samples collected between June 2009 and
September 2010 at the National Oceanic and Atmospheric Administration Boulder
Atmospheric Observatory (BAO; Lat: 40.050° N, Lon:
105.004° W) to derive emission ratios of each species with respect
to CO<sub>2</sub>ff. The BAO tower is situated at the boundary of the Denver
metropolitan area to the south and a large industrial and agricultural region
to the north and east, making it an ideal location to study the contrasting
mix of emissions from the activities in each region. The species considered
in this analysis are carbon monoxide (CO), methane (CH<sub>4</sub>), acetylene
(C<sub>2</sub>H<sub>2</sub>), benzene (C<sub>6</sub>H<sub>6</sub>), and
C<sub>3</sub>–C<sub>5</sub> alkanes. We
estimate emissions for a subset of these species by using the Vulcan high
resolution CO<sub>2</sub>ff emission data product as a reference. We find that CO
is overestimated in the 2008 National Emissions Inventory (NEI08) by a factor
of ~2. A close evaluation of the inventory suggests that the ratio of CO
emitted per unit fuel burned from on-road gasoline vehicles is likely
over-estimated by a factor of 2.5. Using a wind-directional analysis of the
data, we find enhanced concentrations of CH<sub>4</sub>, relative to CO<sub>2</sub>ff, in
air influenced by emissions to the north and east of the BAO tower when
compared to air influenced by emissions in the Denver metro region to the
south. Along with enhanced CH<sub>4</sub>, the strongest enhancements of the
C<sub>3</sub>–C<sub>5</sub> alkanes are also found in the north and east wind sector,
suggesting that both the alkane and CH<sub>4</sub> enhancements are sourced from oil
and gas fields located to the northeast, though it was not possible to rule
out the contribution of non oil and gas CH<sub>4</sub> sources. |
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| ISSN: | 1680-7316 1680-7324 |