The removal of PM2.5 by trees in tropical Andean metropolitan areas: an assessment of environmental change scenarios.

Metropolitan areas in Andean industrialized valleys with a strong geomorphological structure and a pronounced climate experience an increasing degradation of air quality, which motivates environmental policies that include the expansion of tree coverage in urban areas among the mitigation measures. Using the metropolitan area of the Aburrá Valley, Colombia, as a study case, we evaluate the removal of PM2.5 by urban trees with the Urban Forest Effects (UFORE) methodology, considering the potential effect of changing tree covers in the valley for several projected meteorological conditions under climate change and different urban management practices. The estimated removals are sensitive to the number and distribution of available ground stations, with a tendency to overestimate with fewer stations. We found that the marginal gains in removal by additional tree plantings are low in the urbanized settings. In the environmental scenarios, the main limiting factor in the removal is precipitation, compared to changes in tree cover and levels of pollution. Spatially, the increase in total removal depends on the increase in tree cover, with more benefits obtained when trees are in areas with high concentrations of PM2.5. Trees with low values of leaf area index (LAI) seem to optimize the effectiveness of the removal. Seasonally, the greatest removal occurs in rainy months when pollution levels are the highest. Based on our results, the scenarios that meet the plans and programs aimed at improving air quality would achieve removal effectiveness of around 2.5% of the total emissions of PM2.5 with urban trees. Air quality would achieve removal effectiveness of around 2.5% of the total emissions of PM2.5 with urban trees.