Ozone concentration gradients and wind conditions in Norway spruce (Picea abies) forests in Sweden

Ozone concentrations and wind conditions were measured at different heights above ground inside two different Norway spruce forest canopies in Sweden and compared to those outside or above the forests. Compared to high above ground outside or above the canopies, the ozone concentrations inside the Norway spruce forests were reduced 3–8% during mid-day and 10–40% during nighttime. Daylight Accumulated exposure Over a Threshold 40 ppb (AOT40) was reduced 15–45% inside as compared to outside the forest. The horizontal concentration differences between inside and outside the forest were in the order of 3–4%, independently of the height above ground. The ozone concentration difference inside and outside the forest depended on the air turbulence as well as the horizontal wind speed inside the forest. It also depended on the distance to the forest edge in relation to the wind direction. The ozone concentration differences inside and outside the Norway spruce forests were explained by the differences in the rate of dry deposition in relation to the rate of replacement of ozone from higher air layers or by the horizontal wind going into the forest.