Increasing Canopy Cover in Urban Areas David J. Nowak USDA Forest Service Northeastern Research Station Syracuse, NY

Overview Program Benefits Trees and Air Quality Issues

Tree Canopy Cover Affects: Air and surface temperatures Building energy use Ultraviolet radiation loads Climate change Air quality Water quality & flows Social & psychological well-being Aesthetics…

Temperature reduction Removal Emissions Energy Conservation

Literature - Atlanta Case Study Ozone conc. (ppb) Maximum: June 4, 1984 123 20% reduction in natural hydrocarbon emissions 116 Photochemical effect (2o C increase) 121 Biogenic emission effect (2o C increase) 137 Anthropogenic emission effect (2o C increase) 140 14% increase in maximum ozone concentration due to loss of vegetation (Cardelino and Chameides, 1990)

Los Angeles Basin Study Air quality impacts of increased urban tree cover may be locally positive or negative with respect to ozone Net basin-wide effect of increased urban tree cover is a decrease in ozone concentrations if the additional trees are low VOC emitters (Taha, 1996)

Urban Trees and Ozone in the Northeastern United States Increased urban tree cover: Reduced ozone (O3) in urban areas (-1 ppb daytime) Physical effects of trees on pollution removal, air temperature, wind speed and boundary layer height are important Tree removal of NOx lead to increased O3 at night (loss of NOx scavenging of O3) Tree VOC emissions had no detectable (<1 ppb) effect on O3 (Nowak, Civerolo, Rao, Sistla and Luley, 2000)

New York City Area Study 10% increase in urban tree cover Reduced 1-hour maximum O3 by ~4 ppb (132 ppb to 128 ppb) 8-hour maximum O3 by ~1 ppb Little difference in maximum reductions between 10% and 30% tree cover increase Very significant impact 37% reduction in amount needed to gain attainment Additional tree cover will remove thousands of tons of air pollutants per year (Luley et al, 2000)

Issues Remaining Emissions reductions But trees emit; VOC / NOx equivalents Land Use Change (bigger issue than trees) Canopy preservation Monitoring / verification / enforcement Programs vs. tree cover Flexible SIP program Maintenance program

Questions? dnowak@fs.fed.us www.fs.fed.us/ne/syracuse