Tower-based measurements of CO2, CO, and CH4 mole fractions in an urban environment

The Indianapolis Flux Experiment (INFLUX) is focused on demonstrating the utility of dense, tower-based observing networks coupled with aircraft-based measurements, atmospheric boundary layer observations and modeling to determine greenhouse gas emission source location and strength in urban areas. Here we focus on the continuous, in-situ observations of greenhouse gas dry mole fractions. As of August 2012, nine towers in and around Indianapolis, IN, have been deployed measuring greenhouse gas concentrations, with one to three additional sites planned. The sites include a wide variety of landcover types, with rural, suburban, and downtown locations. Four sites are planned to include measurements of the surface energy balance, momentum flux, and short and long wave radiation fluxes. Based on two towers deployed in 2010, the urban enhancement of CO₂ averages 2.4 ppm at 3pm local, whereas that of CO averages 8 ppb. On average, no urban enhancement of CH₄ is observed. With the increased density of greenhouse gas measurements, we will quantify spatial patterns in atmospheric mixing ratios of CO₂, CO, and CH₄ within and around the large urban center. Using observations at several heights on the towers, we will evaluate the performance of the forward model at various heights, thus addressing the question of the required height for these types of measurements. We will also document the diurnal cycle at multiple locations.