Indianapolis flux experiment (INFLUX): Experiment design and new results regarding measurements of urban-area CO ₂ and CH ₄ emission fluxes

Accounting for the global scale sources and sinks of greenhouse gases, as well as development of climate change mitigation strategies, requires a detailed knowledge of the spatial and temporal characteristics of emission fluxes. Recent developments in instrumentation and the deployment of satellite-based instruments enables vast improvements in our ability to define source terms, and to quantify sinks of greenhouse gases, e.g., through inverse modeling. Here we describe the development of, and preliminary observations for 2011 from, the Indianapolis Flux Experiment ("INFLUX"), a multi-institution collaborative study of CO ₂ and CH ₄ emission fluxes for Indianapolis as a test case. INFLUX couples bottom-up and top-down observations, via an array of surface-based instrumented towers and supporting meteorological measurements, and aircraft- based measurements using in situ measurements and flask sampling. We have developed a network of 11 towers at which measurements are made within and around the city. The greenhouse gas measurements rely on Picarro cavity ringdown instruments, and these are supported with meteorological data to define regional atmospheric transport. Flask samples are collected routinely at selected tower locations, and at multiple points during each aircraft flight, and analyzed for a suite of ∼30 greenhouse gas and ancillary species. ¹⁴CO ₂ and CO measurements are being used to constrain the fossil-fuel component of the measured fluxes. Inverse modeling is being conducted using WRF-Chem and the array of surface and aircraft measurements to estimate regional fluxes and their uncertainties. The observations will be compared to the high resolution emissions modeling results provided by the Vulcan and Hestia models. The INFLUX measurements can then be used for comparison to satellite-based column measurements, e.g., from GOSAT. In this paper we will discuss the INFLUX project, and present preliminary results from the towers, aircraft, radiocarbon and stable isotope data, and from the Vulcan/Hestia models.