Multi-scale Top-down Closure of CH4 & CO2 Sources in Indianapolis using Distributed Column and in situ Airborne and Tower Measurements

This work describes a recent collaborative campaign to estimate urban greenhouse gas emissions from Indianapolis, IN, during May 2016. Building on the prior efforts of the Indianapolis Flux Experiment (INFLUX), we combine in-situ measurements made from INFLUX towers, Purdue University's Airborne Laboratory for Atmospheric Research aircraft, and additional ground-based instrumentation, with total column data provided by a network of five Bruker EM27/SUN field-deployable Fourier transform spectrometers (FTS) making solar absorption measurements. The five FTS were deployed in a fixed pattern across the city and used to quantify the difference of column-averaged dry-air mole fractions of CH4 and CO2 across the urban area. These column measurements provide us with an additional top-down estimate of the total mass loading of the atmosphere that is less sensitive to uncertainties in vertical mixing than previous measurement techniques. An inverse-modelling approach is being developed to combine all of the datasets into a spatially resolved estimate of the greenhouse gas flux from the urban area. By bringing together multiple independent measurement methodologies, the campaign also enables us to carefully compare and validate the individual techniques. Here, we present an overview of the entire campaign and highlight the innovative measurement methods used.