Urban Reforestation for Ground-Level Ozone Reduction

Reforestation near metropolitan areas may offer cost-effective ozone reduction

ARLINGTON, VA,  September 08, 2014 – A new study – “Reforestation as a Novel Abatement and Compliance Measure for Ground-Level Ozone” – by The Nature Conservancy, University of Florida, ENVDAT Consulting and The Dow Chemical Company (NYSE: Dow) published in the Proceedings of the National Academy of Sciences (PNAS), suggests that large-scale peri-urban forest restoration (replanting trees around an urban periphery) can help reduce air pollution abatement and compliance costs, while at the same time providing benefits for nature and people that conventional, technological pollution controls do not provide.

“This study has highlighted that forests can play a role in helping address the ozone problem, and they may do so at a cost lower than or comparable to that of additional conventional, engineering-based controls,” said Timm Kroeger, lead author of the study and Senior Environmental Economist for The Nature Conservancy’s Central Science department.

“Adding reforestation projects to their conventional reduction measures could allow regulated emitters to achieve compliance with emission limits at lower cost, while at the same time providing benefits to nature and society at large.”

Despite decades of efforts, ground-level ozone concentrations in many metropolitan areas still threaten human health. In the United States alone, 46 areas with a total population of 123 million people are designated by the US EPA as ozone nonattainment areas because their ambient ozone levels regularly exceed the federal air quality standard for ozone. Ozone forms when nitrogen oxide compounds (NOx) combine with volatile organic compounds (VOCs) in the presence of sunlight. All three are required for the process, so whichever is in shortest supply determines the rate of ozone formation.

While previous studies had shown that forests reduce the levels of both ozone and one of its precursors, nitrogen dioxide, the financial feasibility of using reforestation to remove these pollutants remained unclear. To address this question, the study’s authors developed a methodology to assess how well reforestation along an urban periphery would perform in removing ozone and nitrogen dioxide.

They applied the methodology to design a hypothetical 1000 acre reforestation project in the Houston-Galveston-Brazoria ozone nonattainment area in Texas, where ozone levels regularly exceed federal standards and where there is large scale reforestation potential. The project was designed to maximize pollutant removal per dollar cost by selecting appropriate tree size and density at planting.

The study’s authors estimate that the project could remove more than 200 metric tons of regulated ozone precursor equivalents over a 30 year span, at a cost that compares favorably with additional conventional technological controls. While cost competitiveness in a given case depends on land opportunity costs, cost share opportunities and the generation of carbon offsets, about 10,000 acres of reforestation are required to achieve the same amount of NOx reduction as that achieved by installing one additional conventional control on large industrial boilers or furnaces.

The study found the following:

• Forests surrounding ozone hot spots can reduce ground-level ozone by removing ozone directly and by removing the ozone precursor NO2.
• Reforestation can be a cost effective complement to technological controls in controlling ozone pollution.
• Cost effectiveness is substantially increased when companies can also claim carbon credits.
• There are many areas in the US with ozone pollution problems that would be suitable for reforestation as an ozone abatement measure (see map).

The innovative results from the study highlight how conservation gains could also make business sense for Fortune 500 companies.

“What is really exciting is the broad application potential of this approach across the United States and globally,” said Peter Kareiva, Chief Scientist for The Nature Conservancy. “The findings show that reforestation has widespread applicability in many areas with high ozone levels and provides co-benefits for people and nature that conventional controls do not.”

Source: The Nature Conservancy