Scientists suggest that the size difference is primarily due to differences in ozone exposure. (sciencemag.org)
Such a standard would be based on a cumulative, weighted total of daily 12 - hour ozone exposures to plants and crops over a three - month period. (scientificamerican.com)
When ozone exposure decreased by 10 parts per billion — and was at a level well below the federal air quality standard — the workers were 5.5 percent more productive. (ensia.com)