Abstract
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 km 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.
Highlights
BackgroundEnergy usage and greenhouse gas (GHG) emissions, and a growing proportion of the global population lives in cities
1.1 BackgroundCities concentrate population, energy usage and greenhouse gas (GHG) emissions, and a growing proportion of the global population lives in cities
The increasing trend in atmospheric mole fractions of GHGs is evident from continuous monitoring (NOAA, 2016), and consistent with socio-economic data tracking global consumption of fossil fuels and the greenhouse gas inventory reports provided to the UN Framework Convention on Climate Change (UNFCCC, 2016)
Summary
Energy usage and greenhouse gas (GHG) emissions, and a growing proportion of the global population lives in cities. Measurements have been collected from aircraft (Cambaliza et al, 2014, 2015), towers (Bréon et al, 2015; McKain et al, 2015; Lauvaux et al, 2016), ground-based remote sensing (Wong et al, 2015) and satellite (Kort et al, 2012), and analysis methods have ranged from simple atmospheric mass-balance (Cambaliza et al, 2014, 2015) to complex mesoscale atmospheric modeling efforts merged with Bayesian inversions (Lauvaux et al, 2016) These approaches promise to provide an independent assessment of urban emissions, including quantification of changes in fluxes over time (Lauvaux et al, 2013) and identification of gaps in inventory products. Resolving emissions according to source (e.g. traffic, industry, electric power production, waste management, natural gas infrastructure, urban biosphere) will advance management capacity and process understanding of GHG emissions
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