Estimating Top-down Emissions (2011-2014) of CH4 and CO2 From Los
Angeles by an FTS Atop Mount Wilson
Clare Wong1, Dejian Fu1, Thomas J. Pongetti1, Sally Newman2, Eric A. Kort4, Riley Duren1,
Ying-Kuang Hsu3, Charles E. Miller1, Yuk L. Yung2 and Stanley P. Sander1
1
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, USA
2
California Institute of Technology, Pasadena, USA
3
California Air Resources Board, Sacramento, California, United States
4
University of Michigan, Ann Arbor, Michigan, United States
Megacities, such as Los Angeles, emit significant amount of anthropogenic greenhouse
gases (GHGs). As the world’s population in urban regions is expected to increase from over
50% now to 70% by 2050, monitoring the temporal trends of urban GHG emissions are
necessary to verify regulation policy. Since megacities tend to have large spatially and
temporally varying GHG emission characteristics, it is important to perform measurements
which provide continuous spatio-temporal coverage of the domain. In this study, we
demonstrate the ability to track major greenhouse gases, methane (CH4) and carbon
dioxide (CO2) using ground-based remote sensing technique from Mount Wilson.
Since 2010, in Los Angeles, a Fourier Transform Spectrometer (FTS) has been deployed on
Mount Wilson to measure CO2, CH4, carbon monoxide (CO) the combustion tracer, and
other tracer gases using reflected sunlight in the near-infrared spectral regions. Combining
the unique vista from Mount Wilson and high-precision measurements from the FTS, the
slant column abundances of these trace gases above and within the urban dome of Los
Angeles are acquired. Within the urban dome, continuous daytime temporal and spatial
measurements are recorded for 28 reflection points which are strategically located across
the basin. Here we analyze the path-averaged dry air mixing ratios XCH4, XCO2 and XCO
acquired by the FTS during a three-year period from 2011 to 2014. Using tracer-to-tracer
correlation analysis, we investigate the ratios of XCH4:XCO2, XCH4:XCO and XCO:XCO2 in
excess of the background values. Significant spatio-temporal variability in all three ratios is
observed across the Los Angeles megacity during this measurement period. We then derive
the top-down estimates of basin total CH4 and CO2 emissions between 2011 and 2014 using
the existing bottom-up emission database of CO2 and CO, and compare our estimates to the
emissions reported by the state government and previous studies.
Copyright 2014. California Institute of Technology. Government sponsorship acknowledged.