Ronald Reagan was Right

Those with a long memory might remember Ronnie when campaigning in 1980 , " Trees produce smog ". Oh, how we laughed, what a torrent of denigration poured down upon his head.
Turns out he was right of course. Today's Telegraph

According to a team from York University, when temperatures top 95F (35C), our native plants and trees start emitting "cooling" chemicals such as isoprene and turpene into the atmosphere which in turn encourage the production of ozone.
It is thought that isoprene, which is released by deciduous trees, and turpene, which is emitted by evergreen trees, help protect leaves from heat and sun damage.
In the atmosphere isoprene and turpene act as catalysts, increasing the rate at which sunlight breaks down nitrogen oxide - a car pollutant - into ozone. The more isoprene and turpene there is, the more ozone is produced from smaller amounts of nitrogen oxide.
But Prof David Fowler, director of biogeochemical cycles in the Centre for Ecology and Hydrology in Edinburgh, cautioned against over-reaction. "Most of the human health effects literature on this comes from North America," he said. "Basically, we are getting to where America was 20 to 30 years ago.

Just one more thing he was right about I guess.