Estimating cost effectiveness of residential yard trees for improving air quality in Sacramento, California, using existing models

The ability of shade trees in residential yards in Sacramento, CA, to provide cost-effective air quality control was modelled. Three scenarios of a 100-tree planting project were analyzed; they differed in air-pollutant uptake rates (NO₂, PM₁₀, O₃, and SO₂) and BVOC emissions. Local hourly pollutant concentrations and meteorological data were incorporated into the model, and tree growth and mortality were based on data from Sacramento Shade. To assess cost-effectiveness, tree planting, pruning, and eventual removal costs were determined based on a survey of local garden centers and arborists. These costs were compared to the control costs for the pollutants taken from a Best Available Cost Technology analysis. Ultimately, there was a large range in the benefit-cost ratio for the three scenarios, with the high-deposition/low-BVOC scenario showing a positive ratio and the low-deposition/high-BVOC scenario showing a negative ratio. The authors suggest that air quality benefits alone may not be enough to make tree planting and care cost-effective.