labs_title

Elliptic Cylinder Airborne Sampling and Geostatistical Mass Balance Approach for Quantifying Local Greenhouse Gas Emissions

J.M. Tadić, A.M. Michalak, L. Iraci, V. Ilić, S.C. Biraud, D.R. Feldman, T. Bui, M.S. Johnson, M. Loewenstein, S. Jeong, M.L. Fischer, E.L. Yates and J. Ryoo

In this work, we develop an improved strategy for estimating greenhouse gas emissions at “local” to “urban” scales. The three-pronged approach involved an elliptical cylindrical flight path to better constrain emissions coming from the target region, an onboard meteorological measurement system that eliminated the need for model-based estimates of wind speed and direction, and a geostatistical mass balance approach for rigorous quantification of the mass flux of greenhouse gases from the source. Overall, the approach provides several improvements over the upwind and downwind “curtain” approaches previously used to estimate fluxes at local and urban scales. We demonstrated the approach by quantifying methane emissions from an oil field south of San Ardo, California.


Abstract

In this study, we explore observational, experimental, methodological, and practical aspects of the flux quantification of greenhouse gases from local point sources by using in situ airborne observations, and suggest a series of conceptual changes to improve flux estimates. We address the major sources of uncertainty reported in previous studies by modifying (1) the shape of the typical flight path, (2) the modeling of covariance and anisotropy, and (3) the type of interpolation tools used. We show that a cylindrical flight profile offers considerable advantages compared to traditional profiles collected as curtains, although this new approach brings with it the need for a more comprehensive subsequent analysis. The proposed flight pattern design does not require prior knowledge of wind direction and allows for the derivation of an ad hoc empirical correction factor to partially alleviate errors resulting from interpolation and measurement inaccuracies. The modified approach is applied to a use-case for quantifying CH4 emission from an oil field south of San Ardo, CA, and compared to a bottom-up CH4 emission estimate.

Tadić, J.M., A.M. Michalak, L. Iraci, V. Ilić, S.C. Biraud, D.R. Feldman, T. Bui, M.S. Johnson, M. Loewenstein, S. Jeong, M.L. Fischer, E.L. Yates, J. Ryoo (2017) "Elliptic Cylinder Airborne Sampling and Geostatistical Mass Balance Approach for Quantifying Local Greenhouse Gas Emissions", Environmental Science & Technology, doi:10.1021/acs.est.7b03100.