With drop in LA's vehicular aerosol pollution, vegetation emerges as major source

Organic aerosol pollutants have decreased in the Los Angeles area due to strict vehicle emissions controls, but aerosol levels still rise in hot weather to unhealthful levels. While some attribute these aerosols to household cleaning products, researchers have identified a more probable cause: chemicals emitted by vegetation. Given the number of trees in LA, like the isoprene-emiting Mexican fan palm, it's likely that 25% of organic aerosols are from plants.

source https://www.sciencedaily.com/releases/2021/03/210323150822.htm