Characterization of Fugitive Methane Emissions from Commercial Buildings in California

This project developed and validated methods for site recruitment, field testing, and estimating building-level and statewide methane emissions from commercial buildings in California. Analysis captured post-meter methane emissions data from natural gas appliances and pipe system components from a sample of buildings, then estimated total annual building-level and statewide emissions.
Although there were thousands of measurements at more than 100 buildings, there were only a few measurements for some appliance types for certain building types. Extrapolating these results to a statewide level implies a high level of uncertainty for some building and appliance type combinations. Thus, the total initial estimate should be refined through additional research. The study estimated emissions using the as-measured data and an alternative estimate that gives less weight to observed outliers.
The project team analyzed field data to characterize methane emissions from commercial buildings in California. Combining estimates of emissions from pipe joints and appliances, the team estimated total fugitive methane emissions from commercial buildings across California to be between 540 and 620 million cubic feet per year as measured or 311 to 392 million cubic feet per year for the alternative estimate designed to reduce the impact of outliers. Because of factors such as a limited number of buildings and appliances analyzed and outliers in the sample, the uncertainty associated with this analysis is very high, with a range of emissions spanning approximately 78.6 million to 1.1 billion cubic feet per year.
The study found that most gas piping and equipment in the sample of commercial buildings operated with low to no fugitive methane emissions. A small percentage of sources accounted for most emissions for both analyses. Future studies can apply techniques developed in this project to a larger, more diverse sample of buildings to refine the statewide emissions estimates.