The findings suggested that a 20% loss in the wooded area due to urbanization in Los Angeles would lead to a 14% increase in ozone concentrations. Nowak et al. (2000) provided a more detailed consideration of the net effect on ozone levels for urban areas in the North Eastern United States, but the findings were less clear. The model produced found an increase in tree cover to both increase and decrease ozone levels throughout the day. Between the hours of 5am and 19:00 a net decrease in ozone levels of was recorded due to urban trees, but during the evening there.
