The effects of air quality on trees are being studied at three sites in Britain. Trees are growing in open-top chambers in filtered and ambient air conditions with outside plots to monitor the chamber effect. Results obtained at the end of the 1990 growing season show that Norway spruce. Scots pine and beech grew taller in filtered air than those in ambient air at the Headley (Hampshire) site since the last assessment in 1989. No statistically significant effects on height and diameter increment or plant biomass have been detected for Norway spruce, beech, Scots pine or Sitka spruce at the other two sites (Chatsworth and Glendevon). Visible pollution damage to foliage has not been observed at Headley.
