Methane emissions from dairies in the Los Angeles Basin

We estimate the amount of methane (CH_4) emitted by the largest dairies in the southern California region by combining measurements from four mobile solar-viewing ground-based spectrometers (EM27/SUN), in situ isotopic ^(13∕12)CH_4 measurements from a CRDS analyzer (Picarro), and a high-resolution atmospheric transport simulation with a Weather Research and Forecasting model in large-eddy simulation mode (WRF-LES). The remote sensing spectrometers measure the total column-averaged dry-air mole fractions of CH_4 and CO_2 (X_(CH)_4 and X_(CO)_2) in the near infrared region, providing information on total emissions of the dairies at Chino. Differences measured between the four EM27/SUN ranged from 0.2 to 22 ppb (part per billion) and from 0.7 to 3 ppm (part per million) for X_(CH)_4 and X_(CO)_2, respectively. To assess the fluxes of the dairies, these differential measurements are used in conjunction with the local atmospheric dynamics from wind measurements at two local airports and from the WRF-LES simulations at 111 m resolution. Our top-down CH_4 emissions derived using the Fourier transform spectrometers (FTS) observations of 1.4 to 4.8 ppt s^(−1) are in the low end of previous top-down estimates, consistent with reductions of the dairy farms and urbanization in the domain. However, the wide range of inferred fluxes points to the challenges posed by the heterogeneity of the sources and meteorology. Inverse modeling from WRF-LES is utilized to resolve the spatial distribution of CH_4 emissions in the domain. Both the model and the measurements indicate heterogeneous emissions, with contributions from anthropogenic and biogenic sources at Chino. A Bayesian inversion and a Monte Carlo approach are used to provide the CH_4 emissions of 2.2 to 3.5 ppt s^(−1) at Chino

Evaluation of MOPITT Version 7 joint TIR-NIR XCO retrievals with TCCON

Observations of carbon monoxide (CO) from the Measurements Of Pollution In The Troposphere (MOPITT) instrument aboard the Terra spacecraft were expected to have an accuracy of 10 % prior to the launch in 1999. Here we evaluate MOPITT Version 7 joint (V7J) thermal-infrared and near-infrared (TIR–NIR) retrieval accuracy and precision and suggest ways to further improve the accuracy of the observations. We take five steps involving filtering or bias corrections to reduce scatter and bias in the data relative to other MOPITT soundings and ground-based measurements. (1) We apply a preliminary filtering scheme in which measurements over snow and ice are removed. (2) We find a systematic pairwise bias among the four MOPITT along-track detectors (pixels) on the order of 3–4 ppb with a small temporal trend, which we remove on a global scale using a temporally trended bias correction. (3) Using a small-region approximation (SRA), a new filtering scheme is developed and applied based on additional quality indicators such as the signal-to-noise ratio (SNR). After applying these new filters, the root-mean-squared error computed using the local median from the SRA over 16 years of global observations decreases from 3.84 to 2.55 ppb. (4) We also use the SRA to find variability in MOPITT retrieval anomalies that relates to retrieval parameters. We apply a bias correction to one parameter from this analysis. (5) After applying the previous bias corrections and filtering, we compare the MOPITT results with the GGG2014 ground-based Total Carbon Column Observing Network (TCCON) observations to obtain an overall global bias correction. These comparisons show that MOPITT V7J is biased high by about 6 %–8 %, which is similar to past studies using independent validation datasets on V6J. When using TCCON spectrometric column retrievals without the standard airmass correction or scaling to aircraft (WMO scale), the ground- and satellite-based observations overall agree to better than 0.5 %. GEOS-Chem data assimilations are used to estimate the influence of filtering and scaling to TCCON on global CO and tend to pull concentrations away from the prior fluxes and closer to the truth. We conclude with suggestions for further improving the MOPITT data products

Southern California megacity CO₂, CH₄, and CO flux estimates using ground- and space-based remote sensing and a Lagrangian model

We estimate the overall CO2, CH4, and CO flux from the South Coast Air Basin using an inversion that couples Total Carbon Column Observing Network (TCCON) and Orbiting Carbon Observatory-2 (OCO-2) observations, with the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model and the Open-source Data Inventory for Anthropogenic CO2 (ODIAC). Using TCCON data we estimate the direct net CO2 flux from the SoCAB to be 104&thinsp;±&thinsp;26&thinsp;Tg&thinsp;CO2&thinsp;yr−1 for the study period of July 2013–August 2016. We obtain a slightly higher estimate of 120&thinsp;±&thinsp;30&thinsp;Tg&thinsp;CO2&thinsp;yr−1 using OCO-2 data. These CO2 emission estimates are on the low end of previous work. Our net CH4 (360&thinsp;±&thinsp;90&thinsp;Gg&thinsp;CH4&thinsp;yr−1) flux estimate is in agreement with central values from previous top-down studies going back to 2010 (342–440&thinsp;Gg&thinsp;CH4&thinsp;yr−1). CO emissions are estimated at 487&thinsp;±&thinsp;122&thinsp;Gg&thinsp;CO&thinsp;yr−1, much lower than previous top-down estimates (1440&thinsp;Gg&thinsp;CO&thinsp;yr−1). Given the decreasing emissions of CO, this finding is not unexpected. We perform sensitivity tests to estimate how much errors in the prior, errors in the covariance, different inversion schemes, or a coarser dynamical model influence the emission estimates. Overall, the uncertainty is estimated to be 25&thinsp;%, with the largest contribution from the dynamical model. Lessons learned here may help in future inversions of satellite data over urban areas.</p

Differential column measurements using compact solar-tracking spectrometers

We demonstrate the use of compact solar-tracking Fourier transform spectrometers (Bruker EM27/SUN) for differential measurements of the column-averaged dry-air mole fractions of CH₄ and CO₂ within urban areas. Using Allan variance analysis, we show that the differential column measurement has a precision of 0.01 % for <i>X</i>_CO₂ and <i>X</i>_CH₄ with an optimum integration time of 10 min, corresponding to Allan deviations of 0.04 ppm and 0.2 ppb, respectively. The sensor system is very stable over time and after relocation across the continent. We report tests of the differential column measurement, and its sensitivity to emission sources, by measuring the downwind-minus-upwind column difference Δ<i>X</i>_CH₄ across dairy farms in the Chino area, California, and using the data to verify emissions reported in the literature. Ratios of spatial column differences Δ<i>X</i>_CH₄∕Δ<i>X</i>_CO₂ were observed across Pasadena within the Los Angeles basin, indicating values consistent with regional emission ratios from the literature. Our precise, rapid measurements allow us to determine significant short-term variations (5–10 min) of <i>X</i>_CO₂ and <i>X</i>_CH₄ and to show that they represent atmospheric phenomena.<br><br>Overall, this study helps establish a range of new applications for compact solar-viewing Fourier transform spectrometers. By accurately measuring the small differences in integrated column amounts across local and regional sources, we directly observe the mass loading of the atmosphere due to the influence of emissions in the intervening locale. The inference of the source strength is much more direct than inversion modeling using only surface concentrations and less subject to errors associated with small-scale transport phenomena

TCCON data from East Trout Lake, SK (CA), Release GGG2020.R0

The Total Carbon Column Observing Network (TCCON) is a network of ground-based Fourier Transform Spectrometers that record direct solar absorption spectra of the atmosphere in the near-infrared. From these spectra, accurate and precise column-averaged abundances of atmospheric constituents including CO2, CH4, N2O, HF, CO, H2O, and HDO, are retrieved. This is the GGG2020 data release of observations from the TCCON station at East Trout Lake, CanadaContact person: Wunch, Debra [email protected] available via S3 at https://renc.osn.xsede.org/ini210004tommorrell/10.14291/tccon.ggg2020.easttroutlake01.R0/&lt;/p&gt;README.txt 0.0 GB &lt;a role="button" class="ui compact mini button" href="https://renc.osn.xsede.org/ini210004tommorrell/10.14291/tccon.ggg2020.easttroutlake01.R0/README.txt" &gt; &lt;i class="download icon"&gt;&lt;/i&gt; Download &lt;/a&gt;&lt;/p&gt; et20161003_20220813.public.qc.nc 0.06 GB &lt;a role="button" class="ui compact mini button" href="https://renc.osn.xsede.org/ini210004tommorrell/10.14291/tccon.ggg2020.easttroutlake01.R0/et20161003_20220813.public.qc.nc" &gt; &lt;i class="download icon"&gt;&lt;/i&gt; Download &lt;/a&gt;&lt;/p&gt; et20161003_20220528.public.qc.nc 0.06 GB &lt;a role="button" class="ui compact mini button" href="https://renc.osn.xsede.org/ini210004tommorrell/10.14291/tccon.ggg2020.easttroutlake01.R0/et20161003_20220528.public.qc.nc" &gt; &lt;i class="download icon"&gt;&lt;/i&gt; Download &lt;/a&gt;&lt;/p&gt; et20161003_20220306.public.qc.nc 0.06 GB &lt;a role="button" class="ui compact mini button" href="https://renc.osn.xsede.org/ini210004tommorrell/10.14291/tccon.ggg2020.easttroutlake01.R0/et20161003_20220306.public.qc.nc" &gt; &lt;i class="download icon"&gt;&lt;/i&gt; Download &lt;/a&gt;&lt;/p&gt; LICENSE.txt 0.0 GB &lt;a role="button" class="ui compact mini button" href="https://renc.osn.xsede.org/ini210004tommorrell/10.14291/tccon.ggg2020.easttroutlake01.R0/LICENSE.txt" &gt; &lt;i class="download icon"&gt;&lt;/i&gt; Download &lt;/a&gt;&lt;/p&gt

TCCON data from East Trout Lake, SK (CA), Release GGG2014.R1

The Total Carbon Column Observing Network (TCCON) is a network of ground-based Fourier Transform Spectrometers that record direct solar absorption spectra of the atmosphere in the near-infrared. From these spectra, accurate and precise column-averaged abundances of atmospheric constituents including CO2, CH4, N2O, HF, CO, H2O, and HDO, are retrieved. This data set contains observations from the TCCON station East Trout Lake, SK, Canada.Contact person: Debra Wunch [email protected]

Assessment of errors and biases in retrievals of X_CO₂, X_CH₄, X_CO, and X_N₂O from a 0.5 cm^&ndash;1 resolution solar-viewing spectrometer

Bruker&trade; EM27/SUN instruments are commercial mobile solar-viewing near-IR spectrometers. They show promise for expanding the global density of atmospheric column measurements of greenhouse gases and are being marketed for such applications. They have been shown to measure the same variations of atmospheric gases within a day as the high-resolution spectrometers of the Total Carbon Column Observing Network (TCCON). However, there is little known about the long-term precision and uncertainty budgets of EM27/SUN measurements. In this study, which includes a comparison of 186 measurement days spanning 11 months, we note that atmospheric variations of X_gas within a single day are well captured by these low-resolution instruments, but over several months, the measurements drift noticeably. We present comparisons between EM27/SUN instruments and the TCCON using GGG as the retrieval algorithm. In addition, we perform several tests to evaluate the robustness of the performance and determine the largest sources of errors from these spectrometers. We include comparisons of X_CO₂, X_CH₄, X_CO, and X_N₂O. Specifically we note EM27/SUN biases for January 2015 of 0.03, 0.75, &ndash;0.12, and 2.43 % for X_CO₂, X_CH₄, X_CO, and X_N₂O respectively, with 1<i>σ</i> running precisions of 0.08 and 0.06 % for X_CO₂ and X_CH₄ from measurements in Pasadena. We also identify significant error caused by nonlinear sensitivity when using an extended spectral range detector used to measure CO and N₂O

Intercomparability of X_CO₂ and X_CH₄ from the United States TCCON sites

The Total Carbon Column Observing Network (TCCON) has become the standard for long-term column-averaged measurements of CO2 and CH4. Here, we use a pair of portable spectrometers to test for intra-network bias among the four currently operating TCCON sites in the United States (US). A previous analytical error analysis has suggested that the maximum 2σ site-to-site relative (absolute) bias of TCCON should be less than 0.2 % (0.8 ppm) in XCO2 and 0.4 % (7 ppb) in XCH4. We find here experimentally that the 95 % confidence intervals for maximum pairwise site-to-site bias among the four US TCCON sites are 0.05–0.14 % for XCO2 and 0.08–0.24 % for XCH4. This is close to the limit of the bias we can detect using this methodology

Quantifying the loss of processed natural gas within California's South Coast Air Basin using long-term measurements of ethane and methane

Methane emissions inventories for Southern California's South Coast Air Basin (SoCAB) have underestimated emissions from atmospheric measurements. To provide insight into the sources of the discrepancy, we analyze records of atmospheric trace gas total column abundances in the SoCAB starting in the late 1980s to produce annual estimates of the ethane emissions from 1989 to 2015 and methane emissions from 2007 to 2015. The first decade of measurements shows a rapid decline in ethane emissions coincident with decreasing natural gas and crude oil production in the basin. Between 2010 and 2015, however, ethane emissions have grown gradually from about 13 ± 5 to about 23 ± 3 Gg yr−1, despite the steady production of natural gas and oil over that time period. The methane emissions record begins with 1 year of measurements in 2007 and continuous measurements from 2011 to 2016 and shows little trend over time, with an average emission rate of 413 ± 86 Gg yr−1. Since 2012, ethane to methane ratios in the natural gas withdrawn from a storage facility within the SoCAB have been increasing by 0.62 ± 0.05 % yr−1, consistent with the ratios measured in the delivered gas. Our atmospheric measurements also show an increase in these ratios but with a slope of 0.36 ± 0.08 % yr−1, or 58 ± 13 % of the slope calculated from the withdrawn gas. From this, we infer that more than half of the excess methane in the SoCAB between 2012 and 2015 is attributable to losses from the natural gas infrastructure