Tree-lined avenues and flower-filled central reservations are pretty, but they could be damaging your health. A new study shows that some plants can increase the rate of ozone production by up to 50 times.

Certain plants, such as rosemary, juniper and pine trees, emit chemical compounds known as terpenes, thought to help deter insect predators, or protect the plant from other stresses like high temperatures.

However, when terpenes mix with pollutants (particularly nitrogen oxides from industry and traffic) they react to produce ozone – a key ingredient of photochemical smogs, and a health hazard that can cause breathing difficulties and may cause cancer.

ozone levels exceeded the US Environmental Protection Agency safe standard (an average of 75 parts per billion over an eight-hour period) and in the worst case reached 107ppb.

Some plant species are very low emitters. Shoestring acacia is a great plant: low water use and low terpene emissions