According to a news story from San Francisco Bay Area ABC TV station and online news outlet KGO, “An aircraft that looked like a fighter jet seen making low passes over the Bay Area Thursday [February 21] is the latest weapon scientists are using to fight air pollution, an airborne lab that could someday allow us to breathe cleaner air. It was out to capture ozone and greenhouse gases over the Bay Area in the never-ending battle to control air pollution. One of the under wing pods is equipped as an airborne science lab [powered by Picarro Greenhouse Gas Measurement Technology]. Intakes on the bottom sample the air then exhaust it out the back. Computers do real-time measurement and analysis. The mission is a partnership of NASA Ames, the Bay Area Air Quality Management District, and other agencies.”
See the video below (notice the PICARRO display at the 35 second mark in the video), or read the online article.