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New York City Case Study: Methods of Analysis

Study explores impact of increased urban tree cover on air quality in NYC for implementation in State Plans. Data from 2001-2002 used for modeling scenarios and pollution removal estimates. Results show potential reductions in ozone levels and air pollutants.

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New York City Case Study: Methods of Analysis

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  1. New York City Case Study:Methods of Analysis David J. Nowak USDA Forest Service Northeastern Research Station Syracuse, NY

  2. New York City Study • Goal: investigate the effects of increased urban vegetation on biogenic emissions and pollutant concentrations in the New York City area for potential incorporation in State Implementation Plans

  3. New York City Project 2001-2002 • What is tree cover in NYC domain area? • What is reasonable cover increase? • Could a realistic increase in tree cover have an impact on ozone? Cooperative project with NYS DEC and Davey Resource Group

  4. New York City Analysis • Analyzed aerial photographs to determine space available for new tree cover • Used digital ortho-quad photographs in conjunction with MRLC land cover maps • Modeled three scenarios: • Base case (No change to the 975 urban land use grid cells) • Realistic urban tree cover increase: Convert ~30% of the urban grass cover to urban trees • Maximum urban tree cover increase: Convert all of the urban grass cover to urban trees

  5. Tree Cover Increase • Realistic – based on discussion with NYS DEC State Forester on reasonable amount of tree cover that could be increased (10% increase in tree cover in urban areas – approximately 500 km2) • Maximum – fill all urban grass areas with trees (32% increase in tree cover in urban areas – approximately 1,600 km2)

  6. Modeling System • Meteorology: MM5 (Version 3.4), modified to accommodate 3 urban land use categories • Anthropogenic emissions: EMS-95 • Biogenic emissions: SMOKE-BEIS2 • Photochemistry: MODELS-3/CMAQ • 4 km horizontal grid size • July 12-15, 1995

  7. Land Surface Parameterizations (MM5)

  8. Change in Urban Tree Cover T%, G%, I% - percent tree, grass, and impervious cover, respectively

  9. Biogenic Emissions • Emissions changed only a few percent

  10. Biogenic Emission • Except for isoprene, anthropogenic emissions are comparable to or much larger than biogenic emissions

  11. Pollution Removal • Estimated pollution removal (UFORE model) for realistic tree cover increase 500 km2 of new cover; 1994 data

  12. Domain max. O3 concentration dropped 4.1 ppb 1 hr ozone - Maximum Cover

  13. Domain max. O3 concentration dropped 4.4 ppb 1 hr Ozone – Realistic Cover

  14. Domain max. O3 concentration dropped 0.8 ppb 8 hr Ozone - Maximum Cover

  15. Domain max. O3 concentration dropped 1.0 ppb 8 hr ozone – Realistic Cover

  16. New York City Area Summary • 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 • Some increases in O3 in the domain • Little difference in maximum reductions between 10% and 30% tree cover increase • Very significant impact • 3% reduction in peak ozone levels • 37% reduction in amount needed to gain attainment • Effects of changes in biogenic emissions were minimal, but there is a potential for a slight increase • Additional tree cover will remove thousands of tons of air pollutants per year

  17. Tree Cover Change • CT = CB + CN + CG – CM CT = total canopy cover in model domain in year n CB = existing tree cover in base year CN = canopy increase from new tree planting CG = growth of existing canopy CM = canopy mortality or loss due to natural of human-induced causes

  18. Potential Program Options • Tree planting (↑CN) • Maintenance to promote growth of existing canopies (↑CG) • Protect existing canopy (↓CM) • e.g., ordinances • Education programs (↑CN ↑CG ↓CM) • Public relation campaigns (↑CN ↑CG ↓CM)

  19. Increasing in Tree Cover • Proposed a series of general programs • CN = Canopy increase from planting • 1+ million trees per year for 10 years • Mortality rate has a dramatic effect • May take 30 years to reach cover goals • Cg and Cm • Preservation, protection, ordinances, maintenance and education

  20. Incorporating Urban Vegetation within SIPs • Resource assessment • Modeling the effect of increasing canopy cover on ozone • Developing reasonable management programs that could be used to achieve modeled changes in canopy cover • Incorporating the modeling results and management programs within a SIP

  21. 1) Resource Assessment • Establish baseline • Satellite analyses • Photo interpretation • Ground assessments (leaf biomass by species) • Space available to plant trees

  22. 2) Model Tree Effects • Work with local air quality modelers • Base case vs. future case (change tree cover) • 4 model analyses: • Meteorological effects (MM5) • Anthropogenic emission effects (e.g., EMS-95) • Biogenic emission effects (BEIS) • Integrated model (CAMx), include deposition change and other model results

  23. 3) Develop Tree Program • Work with state and local forestry personnel • Determine from baseline assessment, reasonable amount that tree cover can be increased • Determine programs that can be implemented to reach goal • Tree planting • Canopy preservation • Elimination of mowing (natural regeneration) • Education and public relations

  24. Tree Plan Enforcement and Verification • Determine how program will be verified to ensure and verify that it is successful • Must verify that program worked, not that ozone was reduced • Monitor trees / tree cover vs. • Monitor programs

  25. Tree Cover Verification Options • Remote Sensing • Program Verification • Ground Truth (counting trees)

  26. 4) Incorporate Results in SIP • Work with state officials to incorporate results in SIP • Option: • “Flexible SIP Approval Policy for Nontraditional Measures”: currently being developed by EPA • actions which are voluntary in nature or which have not previously been approved into SIPs because the actions cannot be quantified as accurately as traditional SIP measures due to scientific or technical issues • allows credit to be generated up front

  27. Flexible SIP Approval • develop a protocol, based on best available science, to quantify emission or pollutant reductions for the nontraditional emission reduction program • run the program for a period of time and then evaluate the results • compare the results with the estimated credit and make up any shortfall, if one is found

  28. Issues Remaining • Emissions reductions • But trees emit; VOC / NOx equivalents • Land Use Change (bigger issue than trees) • Models currently assume no change • Canopy preservation • Monitoring / verification / enforcement • Programs vs. tree cover • Ozone Guidance Document on Mitigation Measures (?)

  29. Conclusion • Increased tree cover will likely lead to ozone reductions • There are methods available to incorporate results into SIPs, but issues remain • State Forestry and Air Quality personnel need to work together to address this issues

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