New trees cancel out air pollution cuts

<br /><br /> Industry has dramatically cut its emissions of pollutants, called volatile organic compounds. But those cuts have been more than offset by the amount of VOCs churned out by trees. <br /><br /> The revelation challenges the notion that planting trees is a good way to clean up the atmosphere. When fossil fuels used in industry and automobiles fail to combust completely, they generate VOCs, which react with nitrogen oxides and sunlight to form poisonous ozone in the lower atmosphere. In the past few decades, the introduction of more efficient engines and&nbsp;catalytic converters has dramatically reduced these emissions.<br /><br /> But trees also produce VOCs, which tend to be ignored by scientists modelling the effects of ozone on pollution. So a team led by Drew Purves at Princeton University investigated the impact of newly planted forests on VOC levels in the US.<br /><br /> The researchers used the US Forest Service&nbsp;[Inventory]&nbsp;Analysis, a database of 250,000 randomly sampled forest plots around the country, and the known VOC emission rate for each tree species for the study. <br /><br /> They calculated that vegetal sources of monoterpenes and isoprene rose by up to 17% from the 1980s to the 1990s - equivalent to three times the industrial reductions. <br /><br /> Farmland reverting to scrub, pine plantations and the invasive sweetgum tree were behind most of the increases in the US.<br /><br /> (From NewScientist.com; A. Gosline; 17-Oct-2004)<br /><br />