It is general public knowledge that trees reduce air pollution and usually for combating traffic pollution. This method of abatement has been promoted to the public because the pollutants carried by the air settle and attach to the foliage rather than circulating in our homes and lungs. Thank you trees.
Now that we see that trees and plants are now dead or dying, we could say that the trees did their job, and all is well. All is not well.
Here is one database to check.
For one public agency advisory
For you U2 Bono-on-the-Edge-of-Denial-while-the-ancient-Joshua-Trees-die-off-forever-while-the-Great-EdgerMatic-Power-Weed-Wha-KKK-er-builds-his-Mount-Malibu-bunker.