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In Situ Carbon Dioxide and Methane Measurements from the Los Angeles Megacity Carbon Project



Kristal R. Verhulst, Anna Karion, Jooil Kim, Peter Salameh, Chris Sloop, Ralph Keeling, Ray Weiss, Riley Duren, John B. Miller


Concern about rising greenhouse gas levels has motivated many nations to begin mitigating emissions, motivating the need for robust, consistent, traceable greenhouse gas observation methods in complex urban domains. The Los Angeles (LA) Megacity Carbon Project involves continuous and flask sampling of greenhouse gases, trace gases, and isotopes at surface sites situated throughout the greater Los Angeles area. We report CO2 and CH4 measurements collected from wavelength-scanned cavity ring-down analyzers (Picarro, Inc.) in Los Angeles and nearby counties. All sites use an internally consistent sampling protocol and a single- point calibration method is used to calculate CO2 and CH4 mole fractions in air sample data. We estimate urban CO2 and CH4 enhancements relative to a background condition at the LA sites and discuss various components of uncertainty in the enhancement. Where available, we use experimental data from selected analyzers to estimate uncertainties in the measurement. The uncertainty due to applying a 1-point calibration is found to be the largest component of the analytical uncertainty, and scales as a percentage of the CO2 and CH4 mole fraction measured in the air sample, or roughly 0.25% and 0.3% of the total mole fraction difference relative to the assigned value of the calibration standard. Our observation-based estimates show that the background condition varies substantially depending on the time of year. Overall, the largest component of the uncertainty in the enhancement is due to the background condition, therefore accurate background determination for Los Angeles will require a time-dependent back-trajectory analysis to evaluate background air masses entering the region.
Atmospheric Chemistry and Physics


Verhulst, K. , Karion, A. , Kim, J. , Salameh, P. , Sloop, C. , Keeling, R. , Weiss, R. , Duren, R. and Miller, J. (2017), In Situ Carbon Dioxide and Methane Measurements from the Los Angeles Megacity Carbon Project, Atmospheric Chemistry and Physics, [online], (Accessed July 22, 2024)


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Created July 6, 2017, Updated October 12, 2021