1Department of Chemistry, Purdue University, West Lafayette, IN, USA
2Department of Earth, Atmospheric and Planetary Science & Purdue Climate Change Research Center, Purdue University, West Lafayette, IN, USA
3Department of Aviation Technology, Purdue University, West Lafayette, IN, USA
4Department of Meteorology, The Pennsylvania State University, University Park, PA, USA
5NIST, Gaithersburg, MD, USA
6National Isotope Centre, GNS Science, Lower Hutt, New Zealand
7University of Colorado, Boulder, CO, USA
8NOAA/ESRL, Boulder, CO, USA
9School of Life Sciences, Arizona State University, Tempe, AZ, USA
Received: 23 Jul 2013 – Discussion started: 14 Nov 2013
Abstract. Urban environments are the primary contributors to global anthropogenic carbon emissions. Because much of the growth in CO2 emissions will originate from cities, there is a need to develop, assess, and improve measurement and modeling strategies for quantifying and monitoring greenhouse gas emissions from large urban centers. In this study the uncertainties in an aircraft-based mass balance approach for quantifying carbon dioxide and methane emissions from an urban environment, focusing on Indianapolis, IN, USA, are described. The relatively level terrain of Indianapolis facilitated the application of mean wind fields in the mass balance approach. We investigate the uncertainties in our aircraft-based mass balance approach by (1) assessing the sensitivity of the measured flux to important measurement and analysis parameters including wind speed, background CO2 and CH4, boundary layer depth, and interpolation technique, and (2) determining the flux at two or more downwind distances from a point or area source (with relatively large source strengths such as solid waste facilities and a power generating station) in rapid succession, assuming that the emission flux is constant. When we quantify the precision in the approach by comparing the estimated emissions derived from measurements at two or more downwind distances from an area or point source, we find that the minimum and maximum repeatability were 12 and 52%, with an average of 31%. We suggest that improvements in the experimental design can be achieved by careful determination of the background concentration, monitoring the evolution of the boundary layer through the measurement period, and increasing the number of downwind horizontal transect measurements at multiple altitudes within the boundary layer.
Revised: 30 May 2014 – Accepted: 24 Jul 2014 – Published: 02 Sep 2014
Cambaliza, M. O. L., Shepson, P. B., Caulton, D. R., Stirm, B., Samarov, D., Gurney, K. R., Turnbull, J., Davis, K. J., Possolo, A., Karion, A., Sweeney, C., Moser, B., Hendricks, A., Lauvaux, T., Mays, K., Whetstone, J., Huang, J., Razlivanov, I., Miles, N. L., and Richardson, S. J.: Assessment of uncertainties of an aircraft-based mass balance approach for quantifying urban greenhouse gas emissions, Atmos. Chem. Phys., 14, 9029-9050, doi:10.5194/acp-14-9029-2014, 2014.