AI Summary

Urban greening is praised for cleaning air, but trees also emit biogenic volatile organic compounds that can form ground‑level ozone when they react with sunlight and nitrogen oxides. Human‑made VOCs, found in solvents, paints, cleaning products and fuel vapors, have been regulated and are declining. As cities grow greener and the climate warms, the relative importance of tree‑derived VOCs is expected to rise, potentially increasing ozone risks in hotter, greener cities.

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