(374a) The Role of Forests in Enabling a Sustainable Chemical Facility - a National Analysis

Industrial facilities contribute to about 21% of GHG emissions and close to 50% of pollution in the entire US creating a need to identify novel ways to mitigate these emissions. Most efforts for reducing environmental impact focus on improving systems efficiency to reduce emissions and resource use. By far, the most common method to reduce emissions from industrial sources has been the use of end-of-pipe controls to reduce atmospheric pollutant concentration. Successful implementation of control technologies has helped in maintaining air quality standards to a bare minimum, just enough to meet regulatory limits.  But despite such advances in technology, ecological degradation has shown few signs of slowing down with CO₂ concentration exceeding 400 ppm for the first time in a few million years.

This is mainly because most engineering and human activities have been ignoring the underlying support provided by nature. Ecological systems have the capacity to mitigate the impact of emissions created by engineering activities and supply resources to chemical processes adequate to sustain its functioning. For instance, trees and forests can capture air pollutants by interception of particles on their leaf surface while wetlands have the ability to treat wastewater streams as an alternative to conventional treatment systems. Industries are starting to acknowledge the economic value of ecosystem services and efforts are underway to incorporate the value of natural capital in business bottom line. For example, collaborative efforts between The Nature Conservancy group (TNC) and Dow Chemical have led to the realization that reforestation and land restoration is a novel and practical approach to improve and regulate air quality in an industrial setting. Besides, most industrial facilities have a large amount of land that is mostly left barren and with judicious restoration and protection methods  these sites can provide ecosystem services that are beneficial to both the company and local society.

This talk explores the question, “Is there enough land available around industrial facilities that can be restored to mitigate emissions”   To answer this question, we consider all point sources of emissions  including CO, NO₂, O₃, PM₁₀, PM_2.5, and SO₂ emissions in contiguous US from the National Emissions Inventory database provided by the US EPA. Based on the location of each source, a rural or urban environment parameter was assigned to each point using the National Census data.

We use Gaussian plume models to predict the diffusivity of particles from point sources and to determine their maximum diffusivity from stacks at each location and determine optimal location for land restoration around facilities . Since particle diffusivity along downwind direction is a function of atmospheric stability, wind pattern and local weather conditions, locations with similar atmospheric characteristics were binned to different datasets to determine the maximum diffusivity of particles downwind. Based on the horizontal and vertical diffusivity of particles at multiple points downwind, a range of buffers around point sources were defined to estimate dispersion. For each point source, the longest buffer region was selected and based on the National Land Cover Dataset (NLCD 2011) barren, shrub and grass lands in the buffer regions were masked to determine the amount of land available for reforestation. To account for the amount of forest land that currently exists, forested land cover was also masked.

Nowak et.al [1]  quantified a range of pollutant sequestration values in each county within contiguous US based on the native land cover in the region. Due to a large variability in data for pollutant sequestration between counties within each state, a minimum and a maximum sequestration range for each pollutant was used to identify the land footprint. Land footprint refers to the amount of land that has to be restored in-order to mitigate all the emissions generated by a facility in that particular region. To keep land restoration within size-able and practical limits, point sources within a minimal footprint less than 1 km² were observed further. Using a Euclidean Allocation tool in ArcGIS, the total available land for restoration within the buffer region for each point source was determined.

Preliminary results indicated that for more than 25% of these point sources, restoring the land around these facilities can provide enough services to offset the demand for emissions other than CO2 completely, while less than 2% of industrial facilities required only a slightly larger land area to be restored to offset its emissions. Transportation and warehousing facilities showed the highest potential where restoration of land provided enough ecosystem services to balance the demand followed by the manufacturing, mining and utility generation industries.

A region wise analysis of these facilities indicated that currently most of facilities in the south eastern part of the US have enough forest cover to provide ecosystem services to offset most of the emissions while facilities in the west and south western part of the US have a large amount of unused land that can be restored to provide ecosystem services to support facilities in that region.   

These results indicate that land restoration and reforestation have the potential to be explored as a cost effective alternative to relying on conventional methods for improving air quality.  Land restoration and preservation are becoming an integral part of land management practice to restore degraded ecosystems to its native habitat and are a vital way of increasing the availability of ecosystem services to humanity.

References:

[1] Nowak, D. J., Hirabayashi, S., Bodine, A., & Greenfield, E. (2014). Tree and forest effects on air quality and human health in the United States.Environmental Pollution, 193, 119-129.