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<p>Urban forest (UF) is an effective means of mitigating air pollution. At the stage where PM<sub>2.5</sub>-O<sub>3</sub> composite pollution is prevalent and UF expansion reaches a bottleneck, optimizing UF form based on its area size becomes a superior management strategy. However, existing research has not fully explored the threshold effects of UF size. Using the panel threshold regression model, this study examines relationships between air pollution and UF (size and form) in 305 counties within the Yangtze River Delta (YRD) from 2014 to 2022. The results show (1) UF size exhibits a double threshold effect in three relationships: between patch density (PD) and PM<sub>2.5</sub>, between splitting index (SPLIT) and PM<sub>2.5</sub>, and between SPLIT and O<sub>3</sub>. Meanwhile, a single threshold effect of UF size is observed in relationships between other UF form metrics and pollutant concentrations. (2) When UF size plays the threshold effect in relationships between UF form and pollutant concentrations, its threshold values usually lie around 3%, 14%, and 45%. UF form metrics’ correlations with PM<sub>2.5</sub> are generally opposite to those with O<sub>3</sub>. (3) When UF size is below 45%, PM<sub>2.5</sub> reduction favors complex-shaped and dispersed UF patches, while O<sub>3</sub> reduction benefits from more regular and concentrated UF patches. Once UF size exceeds 45%, a continuous regional UF network can potentially address PM<sub>2.5</sub>-O<sub>3</sub> composite pollution. This study aims to provide insights into atmospheric governance and UF planning.</p>

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Influence of urban forest size and form on PM2.5 and O3 concentrations: A perspective of size threshold

  • 期刊论文

  • 发表日期：

    2025年2月26日

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  • Xin Chen,
  • Fang Wei

摘要

Urban forest (UF) is an effective means of mitigating air pollution. At the stage where PM2.5-O3 composite pollution is prevalent and UF expansion reaches a bottleneck, optimizing UF form based on its area size becomes a superior management strategy. However, existing research has not fully explored the threshold effects of UF size. Using the panel threshold regression model, this study examines relationships between air pollution and UF (size and form) in 305 counties within the Yangtze River Delta (YRD) from 2014 to 2022. The results show (1) UF size exhibits a double threshold effect in three relationships: between patch density (PD) and PM2.5, between splitting index (SPLIT) and PM2.5, and between SPLIT and O3. Meanwhile, a single threshold effect of UF size is observed in relationships between other UF form metrics and pollutant concentrations. (2) When UF size plays the threshold effect in relationships between UF form and pollutant concentrations, its threshold values usually lie around 3%, 14%, and 45%. UF form metrics’ correlations with PM2.5 are generally opposite to those with O3. (3) When UF size is below 45%, PM2.5 reduction favors complex-shaped and dispersed UF patches, while O3 reduction benefits from more regular and concentrated UF patches. Once UF size exceeds 45%, a continuous regional UF network can potentially address PM2.5-O3 composite pollution. This study aims to provide insights into atmospheric governance and UF planning.