Continuous Methane Monitoring

This page was last reviewed on August 16, 2016

July 26th, 2016. After several months of typical ambient methane levels in the Porter Ranch community, 5 methane monitors (Sites 1, 2, 5, 7, 8), previously operated by CARB, have been removed from service in late July 2016. South Coast AQMD will continue to operate real time monitors in accordance to the Aliso Canyon Air Monitoring Plan, and will operate one of the two benzene monitors previously run by CARB. The Air Quality Criteria will now be updated weekly based on real time data from the remaining monitoring sites and the canister samples that will be collected once every six days. CARB continues to make methane measurements in the Los Angeles basin along with its collaborators, and also intends to make additional downwind flights to measure total methane from the Aliso Canyon Natural Gas Storage Facility. The CARB website will be updated whenever new data of that type is available.

In order for the public to be informed about methane concentrations that may be related to the natural gas plume and specifically its potential distribution into the Porter Ranch community, the California Air Resources Board (CARB) and the South Coast AQMD are combining their continuous methane monitoring efforts to display the near-real-time methane monitoring data.  Recent monitoring values are shown in the time series below.

Locations of the continuous methane monitors are shown in the map below:

map showing monitoring sites

Methane is measured in parts per million, or ppm. Normal background is approximately 2 ppm.  Results greater than 3 ppm suggest some additional sources of methane, and results greater than 10 ppm suggest a considerable additional amount of methane is present. 

Data taken directly from the South Coast AQMD automated monitoring system have not been validated extensively and, therefore, are subject to change.  The results from these monitors alone cannot be used to infer health effects, but they do provide a general sense of how much natural gas is in the community at a given time.

Previous South Coast AQMD continuous methane measurements are located here and at the CARB website here. The graph below shows the sharp decrease in ambient methane levels after the gas leak from well SS-25 was stopped on February 12, 2016. 


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