Methane emissions from dairies in the Los Angeles Basin

Abstract

Abstract. 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.

Separation of Methane Emissions From Agricultural and Natural Gas Sources in the Colorado Front Range

“…Excess columns are vertical columns from which a regional vertical column background has been subtracted. Other studies have used the concept of excess columns to quantify CH 4 emissions (Viatte et al, 2017;Wennberg et al, 2012), but this requires coupling with a chemical transport model, which is beyond the scope of this study. Column measurements can also be used to determine emission estimates through a combination of enhancement ratios and emission inventories (Wunch et al, 2009) or long-term trends of enhancement ratios (Franco et al, 2016;Hausmann et al, 2016).…”

MERLIN: A French-German Space Lidar Mission Dedicated to Atmospheric Methane

“…Converting atmospheric observations to surface emissions has been done mostly from global scale to regional scale (e.g., [2]). However, recently, various multi-institution collaborations have developed methodologies for the quantification of methane emissions in urban environments such as in Indianapolis (Indiana) or Los Angeles (California) in the United States (e.g., [18][19][20][21]). The importance of the monitoring of GHG surface fluxes based on atmospheric observations has grown in the context of climate change mitigation after the Paris climate agreement, because it in principle allows emissions and their changes to be tracked with independent data from country-based declarations to the United Nations Framework Convention on Climate Change (UNFCCC).…”

Long open path measurements of greenhouse gases in air using near infrared Fourier transform spectroscopy

“…The OP-in situ differences and geographical scales of these measurements approach the accuracy and resolution of developing regional scale models such as the Weather Research and Forecasting model (WRF) in high resolution mode (Viatte et al, 2017). A detailed high resolution modelling analysis of the measurements presented here is however beyond the scope of this paper.…”