When it’s hot, plants become a surprisingly large source of air pollution
Trees and shrubs emit more chemicals during heat waves that can react to form ozone
![Trees in Berlin](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2017/05/051717_AY_urban-tree_main_FREE.jpg?fit=860%2C460&ssl=1)
FEELING THE HEAT Tree-lined streets in Berlin, shown, offer a lot of benefits for city residents. But during heat waves, the trees, along with other plants, can also contribute to poor air quality, a new study suggests.
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