Title: Application of Gauss's theorem to quantify localized surface emissions from airborne measurements of wind and trace gases

Abstract

Airborne estimates of greenhouse gas emissions are becoming more prevalent with the advent of rapid commercial development of trace gas instrumentation featuring increased measurement accuracy, precision, and frequency, and the swelling interest in the verification of current emission inventories. Multiple airborne studies have indicated that emission inventories may underestimate some hydrocarbon emission sources in US oil- and gas-producing basins. Consequently, a proper assessment of the accuracy of these airborne methods is crucial to interpreting the meaning of such discrepancies. We present a new method of sampling surface sources of any trace gas for which fast and precise measurements can be made and apply it to methane, ethane, and carbon dioxide on spatial scales of ~1000 m, where consecutive loops are flown around a targeted source region at multiple altitudes. Using Reynolds decomposition for the scalar concentrations, along with Gauss's theorem, we show that the method accurately accounts for the smaller-scale turbulent dispersion of the local plume, which is often ignored in other average mass balance methods. With the help of large eddy simulations (LES) we further show how the circling radius can be optimized for the micrometeorological conditions encountered during any flight. Furthermore, by sampling controlled releases of methane and ethane onmore » the ground we can ascertain that the accuracy of the method, in appropriate meteorological conditions, is often better than 10 %, with limits of detection below 5 kg h^-1 for both methane and ethane. Because of the FAA-mandated minimum flight safe altitude of 150 m, placement of the aircraft is critical to preventing a large portion of the emission plume from flowing underneath the lowest aircraft sampling altitude, which is generally the leading source of uncertainty in these measurements. Finally, we show how the accuracy of the method is strongly dependent on the number of sampling loops and/or time spent sampling the source plume.« less

Authors:

Conley, Stephen  ^[1];

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Faloona, Ian ^[2]; Mehrotra, Shobhit ^[2]; Suard, Maxime ^[2]; Lenschow, Donald H.  ^[3];

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Sweeney, Colm ^[4]; Herndon, Scott  ^[5];

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Schwietzke, Stefan  ^[6];

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Pétron, Gabrielle ^[6]; Pifer, Justin ^[7]; Kort, Eric A. ^[8]; Schnell, Russell ^[9]

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+ Show Author Affiliations

1. Univ. of California, Davis, CA (United States). Department of Land, Air, & Water Resources; Scientific Aviation, Inc., Boulder, CO (United States)
2. Univ. of California, Davis, CA (United States). Department of Land, Air, & Water Resources
3. National Center for Atmospheric Research, Boulder, CO (United States). Mesoscale and Microscale Meteorology Laboratory
4. University of Colorado, Boulder, CO (United States). Cooperative Institute for Research in Environmental Sciences
5. Aerodyne Research, Inc, Billerica, MA (United States)
6. University of Colorado, Boulder, CO (United States). Cooperative Institute for Research in Environmental Sciences; NOAA Earth System Research Laboratory, Boulder, CO (United States)
7. Scientific Aviation, Inc., Boulder, CO (United States)
8. Univ. of Michigan, Ann Arbor, MI (United States). Climate and Space Sciences and Engineering
9. NOAA Earth System Research Laboratory, Boulder, CO (United States)

Publication Date:

2017-09-13

Research Org.:

Research Partnership to Secure Energy for America, Houston TX (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1424733

Grant/Contract Number:  

AC26-07NT42677

Resource Type:

Accepted Manuscript

Journal Name:

Atmospheric Measurement Techniques (Online)

Additional Journal Information:

Journal Name: Atmospheric Measurement Techniques (Online); Journal Volume: 10; Journal Issue: 9; Journal ID: ISSN 1867-8548

Publisher:

European Geosciences Union

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES