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Elliptic Cylinder Airborne Sampling and Geostatistical Mass Balance Approach...

Tadic, J. M., A. M. Michalak, L. Iraci, V. Ilic, S. C. Biraud, D. Feldman, T. P. Bui, M. S. Johnson, M. Loewenstein, S. Jeong, M. L. Fischer, E. Yates, and J. Ryoo (2017), Elliptic Cylinder Airborne Sampling and Geostatistical Mass Balance Approach for Quantifying Local Greenhouse Gas Emissions, Environ. Sci. Technol., 51, 10012-10021, doi:10.1021/acs.est.7b03100.

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.

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