The objective of the Indianapolis Flux Experiment (INFLUX) is to develop, evaluate and improve methods for measuring greenhouse gas (GHG) emissions from cities INFLUX’s scientific objectives are to quantify CO2 and CH4 emission rates at 1 km2 resolution with a 10% or better accuracy and precision, to determine whole-city emissions with similar skill, and to achieve high (weekly or finer) temporal resolution at both spatial resolutions The experiment employs atmospheric GHG measurements from both towers and aircraft, atmospheric transport observations and models, and activity-based inventory products to quantify urban GHG emissions Multiple, independent methods for estimating urban emissions are a central facet of our experimental design INFLUX was initiated in 2010 and measurements and analyses are ongoing To date we have quantified urban atmospheric GHG enhancements using aircraft and towers with measurements collected over multiple years, and have estimated whole-city CO2 and CH4 emissions using aircraft and tower GHG measurements, and inventory methods Significant differences exist across methods; these differences have not yet been resolved; research to reduce uncertainties and reconcile these differences is underway Sectorally- and spatially-resolved flux estimates, and detection of changes of fluxes over time, are also active research topics Major challenges include developing methods for distinguishing anthropogenic from biogenic CO2 fluxes, improving our ability to interpret atmospheric GHG measurements close to urban GHG sources and across a broader range of atmospheric stability conditions, and quantifying uncertainties in inventory data products INFLUX data and tools are intended to serve as an open resource and test bed for future investigations Well-documented, public archival of data and methods is under development in support of this objective

/pdf/the-indianapolis-flux-experiment-influx-a-test-bed-for-4irla2c16r.pdf

The Indianapolis Flux Experiment (INFLUX): A test-bed for developing urban greenhouse gas emission measurements.

Global fossil fuel carbon dioxide (FFCO2) emissions will be dictated to a great degree by the trajectory of emissions from urban areas. Conventional methods to quantify urban FFCO2 emissions typica...

/pdf/policy-relevant-assessment-of-urban-co2-emissions-1lumhqdl4r.pdf

Policy-Relevant Assessment of Urban CO2 Emissions

Urban areas contribute approximately three-quarters of fossil fuel derived CO2 emissions, and many cities have enacted emissions mitigation plans. Evaluation of the effectiveness of mitigation efforts will require measurement of both the emission rate and its change over space and time. The relative performance of different emission estimation methods is a critical requirement to support mitigation efforts. Here we compare results of CO2 emissions estimation methods including an inventory-based method and two different top-down atmospheric measurement approaches implemented for the Indianapolis, Indiana, U.S.A. urban area in winter. By accounting for differences in spatial and temporal coverage, as well as trace gas species measured, we find agreement among the wintertime whole-city fossil fuel CO2 emission rate estimates to within 7%. This finding represents a major improvement over previous comparisons of urban-scale emissions, making urban CO2 flux estimates from this study consistent with local and global emission mitigation strategy needs. The complementary application of multiple scientifically driven emissions quantification methods enables and establishes this high level of confidence and demonstrates the strength of the joint implementation of rigorous inventory and atmospheric emissions monitoring approaches.

https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=926815

Synthesis of Urban CO2 Emission Estimates from Multiple Methods from the Indianapolis Flux Project (INFLUX).

The isotopic composition of CO in vehicle exhaust

. Wildfires emit large quantities of aerosols and trace gases, which occasionally reach the lower stratosphere. In August 2017, several pyro-cumulonimbus events injected a large amount of smoke into the stratosphere, observed by lidar and satellites. Satellite observations are in general the main method of detecting these events since in situ aircraft- or balloon-based measurements of atmospheric composition at higher altitudes are not made frequent enough. This work presents accidental balloon-borne trace gas observations of wildfire smoke in the lower stratosphere, identified by enhanced CO mole fractions at approximately 13.6 km. In addition to CO mole fractions, CO2 mole fractions as well as isotopic composition of CO (δ13C and δ18O) have been measured in air samples collected using an AirCore and a LIghtweight Stratospheric Air sampler (LISA) flown on a weather balloon from Sodankyla (4–7 September 2017, 67.37° N, 26.63° E, 179 m a.s.l.), Finland. The greenhouse gas enhancement ratio (∆CO : ∆CO2) and the isotopic signature based on δ13C(CO) and δ18O(CO) independently identify wildfire emissions as the source of the stratospheric CO enhancement. Back-trajectory analysis, performed with the Chemical Lagrangian Model of the Stratosphere (CLaMS), corrected for vertical displacement, due to heating of the wildfire aerosols, by observations made by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument, trace the smoke’s origin to wildfires in British Colombia with an injection date of 12 August 2017. Knowledge of the age of the smoke allowed for a correction of the enhancement ratio, ∆CO : ∆CO2, for the chemical removal of CO by OH. The stable isotope observations were used to estimate the amount of tropospheric air in the plume at the time of observation to be about 34 ± 14 %. The in situ observations provide information on the trace gas chemistry of smoke plumes that reach the stratosphere, as well as the vertical extent of 1 km of the 2017 smoke plume.

/pdf/wildfire-smoke-in-the-lower-stratosphere-identified-by-in-1091jg3xdl.pdf

Wildfire smoke in the lower stratosphere identified by in situ CO observations

We present measurements of CO mole fraction and CO stable isotopes (δ13CO and δC18O) in air during the winters of 2013–14 and 2014–15 at tall tower sampling sites in and around Indianapolis, USA. A tower located upwind of the city was used to quantitatively remove the background CO signal, allowing for the first unambiguous isotopic characterization of the urban CO source and yielding 13CO of –27.7 ± 0.5‰ VPDB and C18O of 17.7 ± 1.1‰ VSMOW for this source. We use the tower isotope measurements, results from a limited traffic study, as well as atmospheric reaction rates to examine contributions from different sources to the Indianapolis CO budget. Our results are consistent with earlier findings that traffic emissions are the dominant source, suggesting a contribution of 96% or more to the overall Indianapolis wintertime CO emissions. Our results are also consistent with the hypothesis that emissions from a small fraction of vehicles without functional catalytic systems dominate the Indianapolis CO budget.

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

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