1. Trees & Air Pollution Cool Communities October 22, 2003
Southern Center for Urban Forestry Research & Information
Dudley R. Hartel
Technology Transfer Specialist
USDA Forest Service
Athens, Georgia
SRS-4901
October 22, 2003

2. Trees & Air Pollution Definitions Processes
Resources (to understand & answer questions)
New Research
October 22, 2003

3. Trees & Air Pollution Definitions VOCs NOx Ozone SMOG
Biogenic & Anthropogenic
October 22, 2003

4. Trees & Air Pollution VOCs Volatile Organic Compounds Many sources
Evaporate readily (vaporize)
Carbon
Many sources
Vegetation
Solvents, paints
Vehicle emissions (benzene)
October 22, 2003

5. Trees & Air Pollution VOCs are a Varied Group
Harmful (toxic) to health
Benzene, PAH (polycyclic aromatic hydrocarbons)
Not harmful to health
Biogenic (NASA study indicates these may reduce airborne molds & bacteria)
October 22, 2003

6. Trees & Air Pollution NOx Emmissions Nitrogen Oxides
Soil, lightning, & volcanoes
Human activity (combustion)
Cars, trucks, electric generation, industry, gasoline powered lawn equipment
Fire (i.e. prescribed burning)
Heavily fertilized agricultural crops (corn, cotton, wheat)
October 22, 2003

7. Trees & Air Pollution Ozone O3 (3 atoms of Oxygen are combined)
Troposphere (up to 10 miles)
Stratosphere ( miles)
October 22, 2003

8. Trees & Air Pollution Ozone
Ozone has the same chemical structure whether it occurs high above the earth or at ground level and can be good or bad, depending on its location in the atmosphere.
Ozone: Good Up High, Bad Nearby
Protects life on earth from the sun’s harmful ultraviolet rays (UV-b)
Creates health problems
October 22, 2003

9. Trees & Air Pollution SMOG Historically: Current:
Industrial SMOG (London 1950s)
Smoke + Fog
Current:
Photochemical SMOG
Non-smoke producing combustion
NOx & VOCs + Sunlight (Ozone)
October 22, 2003

10. Trees & Air Pollution Biogenic Anthropogenic
Produced by living organisms or biological processes
Trees (woody plants)
Grass (herbaceous plants)
Soil
Anthropogenic
Human activity (related to use of fossil fuels)
October 22, 2003

11. Trees & Air Pollution Pollution Process (requirements) Sunlight
Oxides of nitrogen (NOx)
Volatile organic compounds (VOCs)
Temperatures >18 degrees Celsius (64.4F)
October 22, 2003

12. Trees & Air Pollution Trees & VOC Emmisions1 Species Isoprene
Monoterpene
Acer negundo
0.0
0.2
Cedrus deodara
0.4
Quercus alba
0.5
0.1
Quercus rubra
0.9
Pinus taeda
1.4
Pistacia chinensis
2.4
1grams/tree/day Benjamin & Winer 1998
October 22, 2003

13. Trees & Air Pollution Two VOC Emission Issues
Individual species & trees
Benjamin & Winer
Landscape level (regional) for air pollution studies
Guenther & Geron
October 22, 2003

14. Trees & Air Pollution Trees & VOC Emissions YES! Trees Emit VOCs
Terpenes
Isoprene (oak) & monoterpene (pine)
YES! Trees Emit VOCs
VOCs are not pollutants
VOCs + NOx + Sunlight = Problem
October 22, 2003

15. Trees & Air Pollution Resources GHASP Researchers
Galveston-Houston Association for Smog Prevention
Trees & Our Air, 1999
Researchers
Chris Geron & Alex Guenther
Nat’l Center for Atmospheric Research, Boulder, CO
Michael T. Benjamin & Arthur M. Winer
School of Public Health, UCLA
David J. Nowak
USDA FS, Syracuse, NY
October 22, 2003

16. Trees & Air Pollution New Research & Questions
VOC emissions: 2-28x higher than previously recorded (methodology, lab vs. field) for trees
May not be dependent on age of tree
Canopy level may not be important
Considerable variability reported
More research needed
October 22, 2003

17. Trees & Air Pollution Despite Uncertainty in VOC Data Trees:
Do not create pollution!
Have a positive effect on UHI
Evaporative cooling
Shade
Cooler temps mean less ozone, less AC
Remove particulates & CO2
Reduce runoff & erosion
Have a positive impact on mental health
October 22, 2003

18. Trees & Air Pollution Suburban Lawns!
Recent research in Australia (Kirstine)
Grass & cut grass are important sources of VOC emissions
Estimate that about 1/3 of photochemically reactive VOCs in an urban airshed are from grass & grass cutting
These emissions should be part of models
October 22, 2003

19. Trees & Air Pollution Suburban Lawns! Unlike trees, turf does not:
Provide as much evaporative cooling
Provide shade (for humans)
Reduce energy demand
Provide an equivalent (any) pervious surface
Provide mental health benefits (no research)
October 22, 2003

20. Trees & Air Pollution Urbanization effects on tree growth
Jillian W. Gregg, July 10, 2003; Nature
Cottonwood
NYC and surrounding rural sites
Growth better in city
Higher rural O3 levels reduced growth
NOx scavenging reactions in the city reduce O3 levels
Urban pollutants effects extend beyond the urban core
October 22, 2003