Scientists who scanned the skies above dozens of U.S. cities have made a surprising discovery about the smog that’s suspended over Los Angeles: one of its key ingredients isn’t disappearing as fast as it once did.
The finding may help explain why the once-steady improvements in air quality have come close to stalling out here even though nitrogen oxide emissions have continued to decline. It also suggests that the particular chemistry of L.A.’s air may complicate future cleanup efforts.
“That’s certainly part of why we’re in a moment in Los Angeles where it’s harder to get the air cleaner,” said Ronald Cohen, an atmospheric chemist at UC Berkeley who reported the findings in the journal Science.
Cohen and his former graduate student Joshua Laughner identified other cities where levels of nitrogen oxides — known collectively as NOx — have fallen out of tandem with emissions in recent years. But the discrepancy is particularly important for Los Angeles because the pollutant is so abundant here.
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