Fig. 2.

Potential sites in the conterminous United States where reforestation could abate ozone. Sites were identified by intersecting O₃ nonattainment and maintenance areas (80 ppb 1997 8-h standard; ref. 19), NO_x-limited areas (formaldehyde/NO₂ ratio ≥1, from figure 6 in ref. 66), pre-European settlement forested areas [LANDFIRE Biophysical Settings Layer Refresh 2008 (lf_1.1.0), US Department of the Interior, Geological Survey, www.landfire.gov/vegetation.php] and lands presently under grass, shrub or agricultural cover (NLCD2006 Landcover, US Department of the Interior, Geological Survey, www.mrlc.gov/nlcd06_data.php).