Increasing Canopy Cover in Urban Areas

1
Increasing Canopy Cover in Urban Areas

• David J. Nowak
• USDA Forest Service
• Northeastern Research Station
• Syracuse, NY

2
Overview

• Program Benefits
• Trees and Air Quality
• Issues

3
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

4

• Temperature reduction
• Removal
• Emissions
• Energy Conservation

5
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)
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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)
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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 (lt1 ppb)
  effect on O3

(Nowak, Civerolo, Rao, Sistla and Luley, 2000)
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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)
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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

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Questions?

• dnowak_at_fs.fed.us
• www.fs.fed.us/ne/syracuse