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Where do California’s greenhouse gases come from, anyway?

New measurements from aircraft and towers to help state meet aggressive emission reduction mandate

Contact: Dan Krotz, [email protected], (510) 486-4019

Last March, Lawrence Berkeley National Laboratory scientist Marc Fischer boarded a small airplane loaded with air monitoring equipment and crisscrossed the skies above Sacramento and the Bay Area.

Instruments aboard the aircraft measured a cocktail of greenhouse gases: carbon dioxide from fossil fuels, methane from livestock and landfills, nitrous oxide from agriculture, and industrially produced gases such as refrigerants.

The flight was part of the Airborne Greenhouse Gas Emissions Survey, a collaboration between Berkeley Lab, the National Oceanic and Atmospheric Administration, and the University of California, Davis to pinpoint the sources of greenhouse gases in Central California.

The airborne survey is intended to improve inventories of the state’s greenhouse gas emissions, which in turn will help scientists verify the emission reductions mandated by AB-32, the ambitious legislation passed by California in 2006 to slash the state’s greenhouse gas emissions 25 percent by 2020.

“In order to comply with AB-32, we need to know where the gases are coming from and how much,” says Fischer, a scientist in Berkeley Lab’s Environmental Energy Technologies Division.

Members of the collaboration will discuss the project at 5:30 p.m. this Wednesday at the American Geophysical Union’s annual meeting in San Francisco (session #A34D-06).

The aircraft measurements build on the California Greenhouse Gas Emissions Project (CALGEM), which is another Berkeley Lab and National Oceanic and Atmospheric Administration partnership that is partially supported by the California Energy Commission.

In the CALGEM project, round-the-clock greenhouse gas measurements are collected atop San Francisco’s Sutro Tower and a 2000-foot TV antenna in Walnut Grove, California.

Using meteorological data and computer models, the scientists trace the journey of gases collected at the towers back to the areas where the gases originated. They then estimate how much greenhouse gas comes from broad sectors of central California, even from areas that are many miles upwind of the tower.

Their probability-based calculations often match existing inventories of greenhouse gas emissions. Scientists have a good handle on the major greenhouse gas culprits in a region — such as the methane emitted by a landfill or livestock feed lot — thanks to models that utilize economic data and other information that indicate a facility’s day-to-day operations, pollution and all.

“Our findings usually agree with these bottom-up models, but there are surprises,” says Fischer. “Last year, we found that methane emissions in California are higher than the inventory models suggest, and we attributed this discrepancy to extra emissions from cows burping and their manure, which appears to have been previously underestimated.”

In this way, the scientists’ measurements — both from atop towers and from aircraft — will help improve emission models. And improved models means a better inventory of California’s greenhouse gas emissions, which will help policymakers chart a path that ensures the state can meet the aggressive reductions mandated by AB-32.

Lessons learned from the research may also help curb greenhouse gas emissions on a national scale.

“California is the only state that has committed to a very aggressive schedule for greenhouse gas emissions controls,” says Fischer. “The federal government is also contemplating reductions. If so, the U.S. will have to learn how to verify emissions of greenhouse gas emissions nationwide — and the work we are doing here in California will be very useful.”